Tomas
Tropical Storm Tomas is slowly barreling toward western Haiti whilst gradually intensifying. As of the latest NHC intermediate (8:00 PM EDT) advisory, here is the latest information on Tomas:
Wind: 60 mph, with higher gusts
Movement: NNE at 8 mph
Pressure: 993 mb
Location: 16.9°N 75.9°W
Category: Tropical storm
Analysis of shortwave and infrared satellite loops indicate that Tomas is gradually becoming better organized as it approaches western Haiti. Deep convection has increased substantially in both areal coverage and intensity, and now completely covers the circulation center. Additionally, a large, loosely-defined convective band containing heavy precipitation stretches southward to northward for several hundred miles from Panama to Haiti, and then into Tomas' center.
Upper-level outflow is good to the northeast, fair to the east, and poor elsewhere, especially to the south and southwest. The poor outflow in these areas is being caused by 20 kt of southwesterly vertical wind shear associated with an unseasonably strong deep-layer trough and associated cold front currently moving across the Gulf of Mexico and western Atlantic. The latest run of the SHIPS model, however, depicts considerably shear of Tomas, only 13 kt. This is a rather sharp contrast to the aforementioned CIMSS observation. Given high-cloud motions observed on satellite imagery, I am inclined to go with the SHIPS model's assessment of the vertical shear.
The SHIPS model, along with the GFS, the latter of which has its observations based upon output from the SHIPS, forecast an upper-wind environment that is at least marginally conducive to continued gradual intensification of the tropical cyclone before it reaches the coast of eastern Cuba or western Haiti in about 18-24 hours.
Vertical shear is forecast to increase substantially by 30-36 hours, however, as Tomas loses its upper-level support and the upper flow becomes zonal. At that point, there are two scenarios, as depicted in the global model fields:
1. Tomas continues generally northward to north-northeastward under the influence of the aforementioned deep-layer trough, and quickly becomes extratropical as it enters an environment of strong baroclinicity.
2. Tomas instead moves generally eastward, remaining more distant to the trough. While this would prevent the cyclone from becoming extratropical, vertical shear would still be prohibitive enough to allow for the storm to weaken and ultimately dissipate.
The NHC is splitting the difference between the two scenarios, as a sort of compromise. Either way, Tomas will ultimately meet its demise over the western or central Atlantic Ocean over the next several days. Indeed, given the strong vertical shear profiles forecast by both the SHIPS and the GFS, Tomas may not survive throughout the entire forecast period (five days). Rapid weakening is certainly a distinct possibility once Tomas loses its upper-level support and moves into the aforementioned belt of westerly to southwesterly vertical shear.
I anticipate that Tomas will become a minimal hurricane with 75 mph winds over the next 24 hours, provided the center remains offshore. Any deviation to the right of the current NHC forecast track will bring the center of southwestern Haiti.
It is unlikely that Tomas will become anything stronger than an 80 mph hurricane due to an only marginally favorable upper-level wind environment andinteraction with the mountainous terrain of eastern Cuba and western Haiti.
The intensity of Tomas is wholly irrelevant however, as either way, the storm is likely to produce very heavy rains across eastern Cuba and western Haiti through at least Saturday. Like Jeff Masters, I suspect that the heaviest rains associated with Tomas will be found along the southwest and northwest Haitian peninsulas, since the cyclone appears to have moved farther west than what the NHC was predicting this time yesterday. I forecast that anywhere from 5 - 8 inches will fall over these peninsulas, with locally higher amounts. Lesser, but still heavy amounts, in excess of 3 - 6 inches, with locally higher amounts, are possible farther east across the country, both along coastal and inland areas. This includes the capital city of Port-au-Prince, where residents are still living in tents subsequent to the January 12 earthquake, and are also battling a cholera epidemic. Finally, Jamaica can anticipate 1 - 3 inches of rain, with locally higher amounts, particularly along the eastern end of the island, which has the greatest exposure to Tomas' heavy precipitation.
Rainfall in excess of 2 - 4 inches with locally higher amounts is also possible across the Dominican Republic, especially the western portion of the country.
As far as track is concerned, based upon various steering analysis as well as computer model forecasts, I pretty much concur with the NHC's current forecast track, taking the cyclone center across extreme eastern Cuba in about 18 hours, followed by a generally NNE motion with an eventual turn to the NE, then E. However, it is possible that Tomas could come a little more westward and impact more of Cuba and less of Haiti, based upon current CIMSS steering analyses.
However, my own forecast track is a bit west of the NHC's at days three through five, based on various steering data I've analyzed, as it appears that ridging could be a bit stronger than anticipated during that time.
It no longer appears likely that Tomas will stall in the vicinity of Hispaniola. The trough appears to be strong enough to deflect it out to sea, which is great news.
Elsewhere
Elsewhere in the tropics, several of the global models are calling for another tropical depression to form in the eastern or central Caribbean in about 5 - 7 days. The eventual track of this system is uncertain, but right now, there are two possibilities that I see:
1. This system runs into Central America.
2. This system becomes another system that threatens Hispaniola and the Greater Antilles.
It is impossible to choose which scenario is more likely at this juncture. The catalyst for this system could be a perturbation in an unusually active ITCZ, currently near 13N 60W.
We will have to watch this situation closely, as upper-level winds are forecast to begin improving across the central Caribbean during this time.
Thursday, November 4, 2010
Sunday, October 24, 2010
Tropical weather analysis - October 24, 2010
Richard
Hurricane Richard put on a burst of intensification this morning, which brought it to the 10th hurricane of this very active season. The last time 10 or more hurricanes occurred in a season was in 2005, and before that, 1998. Even more remarkable is the 17 named storms we've had. Historical records indicate that the last time this occurred was in 1995, when 19 named storms developed.
As of the latest (4:00 PM CDT) NHC advisory on Richard, here is the latest information:
Wind: 90 mph, with higher gusts
Movement: WNW at 13 mph
Pressure: 981 mb
Location: 17.2°N 88.0°W
Category: 1 (Saffir-Simpson Hurricane Wind Scale)
Visible satellite animations depict a small but well-organized hurricane, with recent images indicating a more symmetrical eye and eyewall. In addition, spiral banding has increased and become more organized as well, particularly to the north.
Doppler radar out of Belize also shows that Richard is a well-organized hurricane.
I suspect that Richard will make landfall between Rockville and Belmopan in about 3-5 hours as an intensifying Category 1 hurricane. It is not out of the question, however, for Richard to attain Category 2 status prior to landfall, and residents of Belize should be vigilant for that possibility.
If this forecast track verifies, Rockville will be on the worst side of the hurricane, and may be close enough to catch Richard's eastern eyewall. Sustained Category 1 force winds (74-95 mph) are possible in this area, with higher gusts.
Sustained tropical storm force winds are already impacting a portion of mainland Belize, and sustained hurricane force winds are not far off, and should begin impacting central Belize in about 2 and a half to 3 hours.
Given that Richard is intensifying, sustained tropical storm force winds will be possible all the way to the western end of the Yucatan Peninsula through Monday night or Tuesday morning. Sustained hurricane force winds may penetrate as far inland as western Belize.
In addition to the wind, Richard is expected to produce a storm surge in excess of 3 to 5 feet near and to the north of where the center makes landfall. This surge will be accompanied by large, destructive waves.
The National Hurricane Center forecasts that 3-6 inches of rain will fall across the Bay Islands, Belize, and the southern Yucatan Peninsula, with lesser amounts (1-2 inches) possible across northern Honduras. They predict that localized amounts could be in excess of 10 inches across the Bay Islands, Belize, and the Yucatan Peninsula.
This pretty much falls in line with my own forecast, and interests in the aforementioned areas should be on alert for the possibility of dangerous, life-threatening flash floods and mudslides, especially in mountainous areas.
As is always the case with landfalling tropical systems, Richard could produce isolated tornadoes, especially in the right-front quadrant.
After landfall, Richard will steadily weaken, and given its small size, it may not survive the trek across Belize and the Yucatan Peninsula.
However, given current organizational trends observed on satellite imagery, along with the fact that these areas aren't terribly mountainous, I expect that Richard will be able to survive the crossing intact (albeit in a severely weakened state, obviously), and will emerge into the southeastern Bay of Campeche in about 36 hours as a severely weakened, vertically tilted tropical depression.
It's worth noting that the 12z GFDL forecasts that Richard will move much slower across Belize, Guatemala, and Mexico. As a result, Richard doesn't enter the Bay of Campeche until much later -- at day three or four. That would coincide with the GFS' forecast of somewhat lower (but still prohibitive) westerly to west-southwesterly vertical wind shear across that portion of the Gulf of Mexico.
Consequently, that model foresees Richard reintensifying to a hurricane before making a second and final landfall near Veracruz, Mexico. However, both the GFDL and the HWRF aren't at all notorious for recognizing obvious shearing conditions, so it's quite likely that this model is failing to appreciate just how fragile Richard will be after crossing the Yucatan, and just how prohibitive zonal shear is to tropical cyclogenesis and intensification.
My own forecast track agrees quite well with the NHC's current one, albeit slightly farther east, as previously noted, for the first 6-12 hours.
The HWRF is an eastern outlier, and forecasts that Richard will accelerate toward the NE toward the Big Bend area of Florida after entering the Gulf of Mexico north of the Yucatan Peninsula. However, the rest of the models are not in agreement with this, and 12z steering forecasts from PSU's e-wall indicate that the low-level flow will be southeasterly, and since Richard is expected to be a very weak tropical cyclone after emerging into the Bay of Campeche, he should move generally NW at that point. Richard would have to maintain some vertical integrity in order for it to follow the track of the HWRF, and this will not be the case.
Sorry JFV, looks like you'll have to wait until next year to get your much fantasized hurricane hit.
Watches and warnings
Invest 90L
A tropical wave in the eastern Atlantic located a few hundred miles west-northwest of the westernmost Cape Verde Islands, dubbed "Invest 90L" by the National Hurricane Center, continues to produce disorganized showers and thunderstorms.
Vertical shear is prohibitively strong, but the GFS predicts that shear will fall in about three to four days as the system moves generally NW, which may allow for some slow development during that time. Indeed, several of the global models eventually foresee this becoming at least a tropical depression. It is not out of the question we could see Tropical Storm Shary from this.
90L is no threat to land areas, nor will it ever be.
Elsewhere
Elsewhere in the tropics, several of the global models, most notably the GFS and ECMWF, are forecasting the development of a tropical cyclone in the eastern Caribbean Sea in about 7-10 days. The latter turns this system into a powerful, westward-moving hurricane, which is a little unnerving. The GFS forecasts that vertical shear will start to lessen in this part of the Caribbean by day seven as well, so this certainly bears watching.
Hurricane Richard put on a burst of intensification this morning, which brought it to the 10th hurricane of this very active season. The last time 10 or more hurricanes occurred in a season was in 2005, and before that, 1998. Even more remarkable is the 17 named storms we've had. Historical records indicate that the last time this occurred was in 1995, when 19 named storms developed.
As of the latest (4:00 PM CDT) NHC advisory on Richard, here is the latest information:
Wind: 90 mph, with higher gusts
Movement: WNW at 13 mph
Pressure: 981 mb
Location: 17.2°N 88.0°W
Category: 1 (Saffir-Simpson Hurricane Wind Scale)
Visible satellite animations depict a small but well-organized hurricane, with recent images indicating a more symmetrical eye and eyewall. In addition, spiral banding has increased and become more organized as well, particularly to the north.
Doppler radar out of Belize also shows that Richard is a well-organized hurricane.
I suspect that Richard will make landfall between Rockville and Belmopan in about 3-5 hours as an intensifying Category 1 hurricane. It is not out of the question, however, for Richard to attain Category 2 status prior to landfall, and residents of Belize should be vigilant for that possibility.
If this forecast track verifies, Rockville will be on the worst side of the hurricane, and may be close enough to catch Richard's eastern eyewall. Sustained Category 1 force winds (74-95 mph) are possible in this area, with higher gusts.
Sustained tropical storm force winds are already impacting a portion of mainland Belize, and sustained hurricane force winds are not far off, and should begin impacting central Belize in about 2 and a half to 3 hours.
Given that Richard is intensifying, sustained tropical storm force winds will be possible all the way to the western end of the Yucatan Peninsula through Monday night or Tuesday morning. Sustained hurricane force winds may penetrate as far inland as western Belize.
In addition to the wind, Richard is expected to produce a storm surge in excess of 3 to 5 feet near and to the north of where the center makes landfall. This surge will be accompanied by large, destructive waves.
The National Hurricane Center forecasts that 3-6 inches of rain will fall across the Bay Islands, Belize, and the southern Yucatan Peninsula, with lesser amounts (1-2 inches) possible across northern Honduras. They predict that localized amounts could be in excess of 10 inches across the Bay Islands, Belize, and the Yucatan Peninsula.
This pretty much falls in line with my own forecast, and interests in the aforementioned areas should be on alert for the possibility of dangerous, life-threatening flash floods and mudslides, especially in mountainous areas.
As is always the case with landfalling tropical systems, Richard could produce isolated tornadoes, especially in the right-front quadrant.
After landfall, Richard will steadily weaken, and given its small size, it may not survive the trek across Belize and the Yucatan Peninsula.
However, given current organizational trends observed on satellite imagery, along with the fact that these areas aren't terribly mountainous, I expect that Richard will be able to survive the crossing intact (albeit in a severely weakened state, obviously), and will emerge into the southeastern Bay of Campeche in about 36 hours as a severely weakened, vertically tilted tropical depression.
It's worth noting that the 12z GFDL forecasts that Richard will move much slower across Belize, Guatemala, and Mexico. As a result, Richard doesn't enter the Bay of Campeche until much later -- at day three or four. That would coincide with the GFS' forecast of somewhat lower (but still prohibitive) westerly to west-southwesterly vertical wind shear across that portion of the Gulf of Mexico.
Consequently, that model foresees Richard reintensifying to a hurricane before making a second and final landfall near Veracruz, Mexico. However, both the GFDL and the HWRF aren't at all notorious for recognizing obvious shearing conditions, so it's quite likely that this model is failing to appreciate just how fragile Richard will be after crossing the Yucatan, and just how prohibitive zonal shear is to tropical cyclogenesis and intensification.
My own forecast track agrees quite well with the NHC's current one, albeit slightly farther east, as previously noted, for the first 6-12 hours.
The HWRF is an eastern outlier, and forecasts that Richard will accelerate toward the NE toward the Big Bend area of Florida after entering the Gulf of Mexico north of the Yucatan Peninsula. However, the rest of the models are not in agreement with this, and 12z steering forecasts from PSU's e-wall indicate that the low-level flow will be southeasterly, and since Richard is expected to be a very weak tropical cyclone after emerging into the Bay of Campeche, he should move generally NW at that point. Richard would have to maintain some vertical integrity in order for it to follow the track of the HWRF, and this will not be the case.
Sorry JFV, looks like you'll have to wait until next year to get your much fantasized hurricane hit.
Watches and warnings
A HURRICANE WARNING IS IN EFFECT FOR...
* BELIZE
A HURRICANE WATCH IS IN EFFECT FOR...
* EAST COAST OF YUCATAN MEXICO FROM PUNTA GRUESA TO CHETUMAL
A TROPICAL STORM WARNING IS IN EFFECT FOR...
* EAST COAST OF YUCATAN MEXICO FROM PUNTA GRUESA TO CHETUMAL
Invest 90L
A tropical wave in the eastern Atlantic located a few hundred miles west-northwest of the westernmost Cape Verde Islands, dubbed "Invest 90L" by the National Hurricane Center, continues to produce disorganized showers and thunderstorms.
Vertical shear is prohibitively strong, but the GFS predicts that shear will fall in about three to four days as the system moves generally NW, which may allow for some slow development during that time. Indeed, several of the global models eventually foresee this becoming at least a tropical depression. It is not out of the question we could see Tropical Storm Shary from this.
90L is no threat to land areas, nor will it ever be.
Elsewhere
Elsewhere in the tropics, several of the global models, most notably the GFS and ECMWF, are forecasting the development of a tropical cyclone in the eastern Caribbean Sea in about 7-10 days. The latter turns this system into a powerful, westward-moving hurricane, which is a little unnerving. The GFS forecasts that vertical shear will start to lessen in this part of the Caribbean by day seven as well, so this certainly bears watching.
Friday, October 22, 2010
Tropical weather analysis - October 22, 2010
Richard
Tropical Storm Richard is slowly intensifying. As of the most recent NHC advisory, here is the latest information on Richard:
Wind: 45 mph, with higher gusts
Movement: W at 5 mph
Pressure: 1005 mb
Location: 16.2°N 81.7°W
Category: Tropical storm
Visible satellite animations suggest that the center is located underneath the mass of deep convection, but the imagery also suggests some vertical shearing over the system. However, there are some indications that this shear is lessening. Additionally, Richard's cyclonic circulation appears to be wrapping some stratocumulus clouds into the western semicircle. Indeed, the latest run of the SHIPS model places 700-500 mb relative humidity values at only 59%, suggesting a very dry mid-level airmass. Finally, Richard's overall circulation envelope appears to be a bit elongated, as evidenced by low-cloud motions observed on satellite imagery. These factors should prevent any rapid intensification of Richard for now.
The dry air and shear notwithstanding, Richard certainly has the potential to become a formidable hurricane over the next several days, as upper-level winds are forecast to be quite favorable for intensification. There are also some indications on water vapor imagery that the very dry airmass is gradually moistening, and high cloud motions derived from satellite imagery imply a lessening of the aforementioned vertical shear.
I expect continued slow intensification of Richard over the next 18 hours, with a more steady rate of strengthening thereafter. However, the potential certainly exists for Richard to rapidly intensify beyond that time, given the very high oceanic heat content located across the western Caribbean Sea, and the light vertical shear profiles forecast.
I expect that by 24 hours, Richard will have become a hurricane.
Richard is currently located in a col region between a developing anticyclone across the Gulf of Mexico and a very potent longwave trough over the western and central Atlantic. This synoptic scale setup indicates that Richard will move only slowly in the short-term. Some erratic motion cannot be ruled out, as well.
Models are split into two camps: the first set, comprised of the CMC, NOGAPS, and UKMET forecast a much weaker Richard. As a result, a shortwave trough and associated cold front that is forecast by the models to branch off from the base of a longwave trough over the high plains/upper midwest in about three days has little appreciable effect on the cyclone. Should this scenario verify, Richard would move into Central America in about two to three days, and eventually into northeast Mexico or south Texas. In fact, the CMC and NOGAPS even lose Richard's circulation over the rugged terrain of Central America.
The latter set of models, comprised of the GFS, HWRF, GFDL, and ECMWF, forecast a deeper, more vertically respectable Richard to respond more significantly to the trough. As a result, these models have Richard turning NW to NNW in about four days toward a developing weakness in the ridge due to a southward movement of said trough toward the Gulf Coast states. In this scenario, Richard would expected to be in the eastern Bay of Campeche in the Gulf of Mexico at that time.
Given current trends, which suggests slow organization (but Richard is still undoubtedly struggling), as well as the forecast of an improving upper wind and thermodynamic environment, which appears to be happening as we speak, I will side with the latter camp.
This track tends to agree pretty well with the NHC's current one, although I am a bit farther to the east of their forecast track at days four and five.
Richard does not pose a significant threat to the United States, as vertical shear profiles are forecast to be quite unfavorable across the Gulf of Mexico. In fact, dissipation of Richard well before "landfall" can be expected. However, Central America and the Yucatan Peninsula may not be so fortunate. The GFDL brings Richard up to Category 4 strength before it slams it into northeastern Belize in about 66-72 hours.
Interests in Honduras, Belize, the Yucatan Peninsula should closely follow the progress of this system over the next several days. Richard could also pose a long-range rainfall threat for from the central Texas to southwest Louisiana coasts, and interests in those areas should also follow the progress of Richard over the next few days.
Again, I want to reiterate that the US is unlikely to see anything more than a little bit of rain from Richard's remnants. Richard will NOT be an organized tropical system by the time it reaches any of the aforementioned areas. However, the rainfall could be locally heavy depending on how moist the environment gets with the approach of said cold front. Tropical systems are notorious for entraining moisture into approaching cold fronts, which can in turn create some serious rainfall and associated flood potential.
Since these areas are in a drought though, the rainfall is unlikely to cause significant flooding problems for Texas and Louisiana.
The most likely target for Richard's Central American landfall is Belize, and for its US landfall, western Louisiana, near Cameron.
Watches and warnings
A HURRICANE WATCH IS IN EFFECT FOR...
* HONDURAS FROM THE NICARAGUA/HONDURAS BORDER WESTWARD TO LIMON AND
THE BAY ISLANDS
* EAST COAST OF MEXICO FROM PUNTA GRUESA TO CHETUMAL
A TROPICAL STORM WARNING IS IN EFFECT FOR...
* HONDURAS FROM THE NICARAGUA/HONDURAS BORDER WESTWARD TO LIMON AND
THE BAY ISLANDS
A TROPICAL STORM WATCH IS IN EFFECT FOR...
* HONDURAS FROM WEST OF LIMON TO THE GUATEMALA BORDER.
* BELIZE
Invest 90L
A strong tropical wave is located near the Cape Verde Islands. This wave has been dubbed "Invest 90L" by the National Hurricane Center. The associated shower activity has become a little better organized, but upper-level winds are only marginally conducive for development, and a less favorable upper wind environment is forecast over the next 12-24 hours. Indeed, southwesterly shear is rapidly approaching the system.
This system does not pose a threat to any land areas, and can be expected to move NW to NNW throughout the forecast period.
Elsewhere
Elsewhere in the tropics, the GFS and ECMWF are indicating that tropical cyclogenesis might occur in the eastern Caribbean in about 7-10 days. This could occur as the ITCZ lifts northward with the approach of the upward MJO.
Since the GFS has been particularly fluent in sniffing out long-range storms this year, I would not discount this possibility at all. However, upper-level winds will not be particularly favorable for development over that part of the Caribbean, so no significant intensification should be expected if this system does form.
Tropical Storm Richard is slowly intensifying. As of the most recent NHC advisory, here is the latest information on Richard:
Wind: 45 mph, with higher gusts
Movement: W at 5 mph
Pressure: 1005 mb
Location: 16.2°N 81.7°W
Category: Tropical storm
Visible satellite animations suggest that the center is located underneath the mass of deep convection, but the imagery also suggests some vertical shearing over the system. However, there are some indications that this shear is lessening. Additionally, Richard's cyclonic circulation appears to be wrapping some stratocumulus clouds into the western semicircle. Indeed, the latest run of the SHIPS model places 700-500 mb relative humidity values at only 59%, suggesting a very dry mid-level airmass. Finally, Richard's overall circulation envelope appears to be a bit elongated, as evidenced by low-cloud motions observed on satellite imagery. These factors should prevent any rapid intensification of Richard for now.
The dry air and shear notwithstanding, Richard certainly has the potential to become a formidable hurricane over the next several days, as upper-level winds are forecast to be quite favorable for intensification. There are also some indications on water vapor imagery that the very dry airmass is gradually moistening, and high cloud motions derived from satellite imagery imply a lessening of the aforementioned vertical shear.
I expect continued slow intensification of Richard over the next 18 hours, with a more steady rate of strengthening thereafter. However, the potential certainly exists for Richard to rapidly intensify beyond that time, given the very high oceanic heat content located across the western Caribbean Sea, and the light vertical shear profiles forecast.
I expect that by 24 hours, Richard will have become a hurricane.
Richard is currently located in a col region between a developing anticyclone across the Gulf of Mexico and a very potent longwave trough over the western and central Atlantic. This synoptic scale setup indicates that Richard will move only slowly in the short-term. Some erratic motion cannot be ruled out, as well.
Models are split into two camps: the first set, comprised of the CMC, NOGAPS, and UKMET forecast a much weaker Richard. As a result, a shortwave trough and associated cold front that is forecast by the models to branch off from the base of a longwave trough over the high plains/upper midwest in about three days has little appreciable effect on the cyclone. Should this scenario verify, Richard would move into Central America in about two to three days, and eventually into northeast Mexico or south Texas. In fact, the CMC and NOGAPS even lose Richard's circulation over the rugged terrain of Central America.
The latter set of models, comprised of the GFS, HWRF, GFDL, and ECMWF, forecast a deeper, more vertically respectable Richard to respond more significantly to the trough. As a result, these models have Richard turning NW to NNW in about four days toward a developing weakness in the ridge due to a southward movement of said trough toward the Gulf Coast states. In this scenario, Richard would expected to be in the eastern Bay of Campeche in the Gulf of Mexico at that time.
Given current trends, which suggests slow organization (but Richard is still undoubtedly struggling), as well as the forecast of an improving upper wind and thermodynamic environment, which appears to be happening as we speak, I will side with the latter camp.
This track tends to agree pretty well with the NHC's current one, although I am a bit farther to the east of their forecast track at days four and five.
Richard does not pose a significant threat to the United States, as vertical shear profiles are forecast to be quite unfavorable across the Gulf of Mexico. In fact, dissipation of Richard well before "landfall" can be expected. However, Central America and the Yucatan Peninsula may not be so fortunate. The GFDL brings Richard up to Category 4 strength before it slams it into northeastern Belize in about 66-72 hours.
Interests in Honduras, Belize, the Yucatan Peninsula should closely follow the progress of this system over the next several days. Richard could also pose a long-range rainfall threat for from the central Texas to southwest Louisiana coasts, and interests in those areas should also follow the progress of Richard over the next few days.
Again, I want to reiterate that the US is unlikely to see anything more than a little bit of rain from Richard's remnants. Richard will NOT be an organized tropical system by the time it reaches any of the aforementioned areas. However, the rainfall could be locally heavy depending on how moist the environment gets with the approach of said cold front. Tropical systems are notorious for entraining moisture into approaching cold fronts, which can in turn create some serious rainfall and associated flood potential.
Since these areas are in a drought though, the rainfall is unlikely to cause significant flooding problems for Texas and Louisiana.
The most likely target for Richard's Central American landfall is Belize, and for its US landfall, western Louisiana, near Cameron.
Watches and warnings
A HURRICANE WATCH IS IN EFFECT FOR...
* HONDURAS FROM THE NICARAGUA/HONDURAS BORDER WESTWARD TO LIMON AND
THE BAY ISLANDS
* EAST COAST OF MEXICO FROM PUNTA GRUESA TO CHETUMAL
A TROPICAL STORM WARNING IS IN EFFECT FOR...
* HONDURAS FROM THE NICARAGUA/HONDURAS BORDER WESTWARD TO LIMON AND
THE BAY ISLANDS
A TROPICAL STORM WATCH IS IN EFFECT FOR...
* HONDURAS FROM WEST OF LIMON TO THE GUATEMALA BORDER.
* BELIZE
Invest 90L
A strong tropical wave is located near the Cape Verde Islands. This wave has been dubbed "Invest 90L" by the National Hurricane Center. The associated shower activity has become a little better organized, but upper-level winds are only marginally conducive for development, and a less favorable upper wind environment is forecast over the next 12-24 hours. Indeed, southwesterly shear is rapidly approaching the system.
This system does not pose a threat to any land areas, and can be expected to move NW to NNW throughout the forecast period.
Elsewhere
Elsewhere in the tropics, the GFS and ECMWF are indicating that tropical cyclogenesis might occur in the eastern Caribbean in about 7-10 days. This could occur as the ITCZ lifts northward with the approach of the upward MJO.
Since the GFS has been particularly fluent in sniffing out long-range storms this year, I would not discount this possibility at all. However, upper-level winds will not be particularly favorable for development over that part of the Caribbean, so no significant intensification should be expected if this system does form.
Wednesday, October 13, 2010
Tropical weather analysis - October 13, 2010
Paula
Extremely tiny Hurricane Paula has weakened steadily throughout the day today, and is now only a Category 1 hurricane. Here is the latest information on this system as of the 11:00 PM CDT advisory from the National Hurricane Center:
Wind: 80 mph, with higher gusts
Movement: NE at 3 mph
Pressure: 993 mb
Location: 21.9°N 85.4°W
Category: 1 (Saffir-Simpson Hurricane Wind Scale)
Analysis of infrared satellite animations suggest that Paula's circulation might be becoming somewhat exposed along the southwestern edge of the CDO. Indeed, high cloud motions observed on said imagery indicate that the hurricane is experiencing southwesterly vertical shear associated with a mid- to upper-level trough and associated cold front currently draped across the central Gulf of Mexico. CIMSS analysis indicates that this shear is prohibitively strong, at 30 kt.
Upper-level outflow is nonexistent to the southwest and quickly going in that direction on the western side as a consequence of the aforementioned shear.
Paula should continue to gradually spin down due to continued southwesterly then westerly vertical shear, and it would not surprise me at all to see Paula dissipate in as little as 36 hours if it manages to track directly over the mountainous terrain of Cuba. Since I suspect Paula will track just north of the Cuban coast after passing the hurricane warning area, I will not forecast such rapid dissipation at this time, but I do expect that Paula will have dissipated by 60 hours.
Analysis of water vapor imagery implies that Paula is already embedded within the mid-latitude southwesterly flow associated with the aforementioned trough. As such, the hurricane is now recurving, albeit at a painfully slow forward motion for the time being, as the approach of said trough has briefly weakened the steering currents surrounding the storm, as is usually the case just prior to and just after recurvature.
Based on various steering data I've analyzed, both real time and forecast, it appears that the trough responsible for Paula's current recurvature will not be strong enough to fully recurve Paula out to sea. All of the models, with the exception of the GFDL, which loses Paula north of Hispaniola in five days, suggest that that a severely weakened or dissipated Paula will eventually move southward back into the western Caribbean Sea underneath the northerly flow associated with the backside of the trough, which is forecast to eventually become a powerful Nor'easter.
Some, such as the NOGAPS, go even further and forecast Paula, or its remnants, to move NW into the southern Gulf of Mexico along the southwestern periphery of a building ridge across the Gulf of Mexico in about five days or so.
Needless to say, confidence in the forecast track beyond two days is not high.
Right now, I my forecast track is just a bit to the south (about 75-100 miles) of the 18z GFDL for the first 48 hours, and just north of NHC's current forecast track during that time.
After 48 hours, my forecast track agrees pretty strongly with that of the NHC, albeit a tad farther westward at the end of the forecast period.
Watches and warnings
A HURRICANE WARNING IS IN EFFECT FOR...
* THE CUBAN PROVINCE OF PINAR DEL RIO
A TROPICAL STORM WARNING IS IN EFFECT FOR...
* THE CUBAN PROVINCES OF LA HABANA AND CUIDAD DE LA HABANA
A TROPICAL STORM WATCH IS IN EFFECT FOR...
* THE FLORIDA KEYS FROM CRAIG KEY WESTWARD...INCLUDING THE DRY
TORTUGAS
Heavy rainfall in excess of 4 to 8 inches, with locally higher amounts, are possible across portions of western and central Cuba over the next couple of days, along with sustained hurricane force winds along the western and extreme west-central sections of the country, and residents in those areas should closely monitor the progress of Paula over the next couple days.
A storm surge in excess of 3 to 6 feet is possible across extreme western Cuba, which will be accompanied by large, destructive waves.
Elsewhere
Elsewhere in the tropics, most of the global models are indicating another tropical cyclone will develop in the Caribbean, this one north of Panama. The time frame is about a week, which, though still quite far out, is one where we need to start paying attention, especially given the model consensus with this.
The GFS suggests that an anticyclonic environment will develop across the southwest Caribbean at about that time, so this will need to be watched closely.
Extremely tiny Hurricane Paula has weakened steadily throughout the day today, and is now only a Category 1 hurricane. Here is the latest information on this system as of the 11:00 PM CDT advisory from the National Hurricane Center:
Wind: 80 mph, with higher gusts
Movement: NE at 3 mph
Pressure: 993 mb
Location: 21.9°N 85.4°W
Category: 1 (Saffir-Simpson Hurricane Wind Scale)
Analysis of infrared satellite animations suggest that Paula's circulation might be becoming somewhat exposed along the southwestern edge of the CDO. Indeed, high cloud motions observed on said imagery indicate that the hurricane is experiencing southwesterly vertical shear associated with a mid- to upper-level trough and associated cold front currently draped across the central Gulf of Mexico. CIMSS analysis indicates that this shear is prohibitively strong, at 30 kt.
Upper-level outflow is nonexistent to the southwest and quickly going in that direction on the western side as a consequence of the aforementioned shear.
Paula should continue to gradually spin down due to continued southwesterly then westerly vertical shear, and it would not surprise me at all to see Paula dissipate in as little as 36 hours if it manages to track directly over the mountainous terrain of Cuba. Since I suspect Paula will track just north of the Cuban coast after passing the hurricane warning area, I will not forecast such rapid dissipation at this time, but I do expect that Paula will have dissipated by 60 hours.
Analysis of water vapor imagery implies that Paula is already embedded within the mid-latitude southwesterly flow associated with the aforementioned trough. As such, the hurricane is now recurving, albeit at a painfully slow forward motion for the time being, as the approach of said trough has briefly weakened the steering currents surrounding the storm, as is usually the case just prior to and just after recurvature.
Based on various steering data I've analyzed, both real time and forecast, it appears that the trough responsible for Paula's current recurvature will not be strong enough to fully recurve Paula out to sea. All of the models, with the exception of the GFDL, which loses Paula north of Hispaniola in five days, suggest that that a severely weakened or dissipated Paula will eventually move southward back into the western Caribbean Sea underneath the northerly flow associated with the backside of the trough, which is forecast to eventually become a powerful Nor'easter.
Some, such as the NOGAPS, go even further and forecast Paula, or its remnants, to move NW into the southern Gulf of Mexico along the southwestern periphery of a building ridge across the Gulf of Mexico in about five days or so.
Needless to say, confidence in the forecast track beyond two days is not high.
Right now, I my forecast track is just a bit to the south (about 75-100 miles) of the 18z GFDL for the first 48 hours, and just north of NHC's current forecast track during that time.
After 48 hours, my forecast track agrees pretty strongly with that of the NHC, albeit a tad farther westward at the end of the forecast period.
Watches and warnings
A HURRICANE WARNING IS IN EFFECT FOR...
* THE CUBAN PROVINCE OF PINAR DEL RIO
A TROPICAL STORM WARNING IS IN EFFECT FOR...
* THE CUBAN PROVINCES OF LA HABANA AND CUIDAD DE LA HABANA
A TROPICAL STORM WATCH IS IN EFFECT FOR...
* THE FLORIDA KEYS FROM CRAIG KEY WESTWARD...INCLUDING THE DRY
TORTUGAS
Heavy rainfall in excess of 4 to 8 inches, with locally higher amounts, are possible across portions of western and central Cuba over the next couple of days, along with sustained hurricane force winds along the western and extreme west-central sections of the country, and residents in those areas should closely monitor the progress of Paula over the next couple days.
A storm surge in excess of 3 to 6 feet is possible across extreme western Cuba, which will be accompanied by large, destructive waves.
Elsewhere
Elsewhere in the tropics, most of the global models are indicating another tropical cyclone will develop in the Caribbean, this one north of Panama. The time frame is about a week, which, though still quite far out, is one where we need to start paying attention, especially given the model consensus with this.
The GFS suggests that an anticyclonic environment will develop across the southwest Caribbean at about that time, so this will need to be watched closely.
Tuesday, October 12, 2010
Tropical weather analysis - October 12, 2010
Paula
Hurricane Paula became a Category 2 hurricane early this afternoon. As of the latest NHC advisory (7:00 PM CDT), here is the latest information on Paula:
Wind: 100 mph, with higher gusts
Movement: N at 9 mph
Pressure: 981 mb
Location: 19.6°N 86.0°W
Category: 2 (Saffir-Simpson Hurricane Wind Scale)
Infrared satellite animations show that Paula is a very small but well-organized hurricane, with a well-defined poleward (north) and equatorial (west) outflow channels due to an amplifying upper trough currently moving across the deep south. However, outflow remains quite restricted to the east, and particularly to the south, due to 20 kt of southerly vertical wind shear analyzed by University of Wisconsin CIMSS. This shear is being induced by a well-defined mid- to upper-level ridge to the east.
An eye is not currently present using conventional satellite imagery, but it was earlier, and all indications are that Paula has maintained her strength over the last couple of hours.
Doppler radar out of Cancun, Mexico shows that Paula has a very small eye, and earlier reconnaissance reports indicates that the eye is no more than, say, 10-15 miles wide. Indeed, if I hadn't been forecasting these systems for three years, I would not, as a layman, be able to readily tell just where Paula's eye is using the aforementioned radar imagery.
I've never seen a Caribbean hurricane as small as Paula, except for perhaps Hurricane Iris in 2001, and even that's iffy since the latter had a larger radius of tropical storm force winds.
Steering analysis from CIMSS indicate that Paula is moving northward under the influence of the aforementioned anticyclone to the east.
Once this shear gets into the core, then rapid weakening is possible, given the hurricane's small size. Shear is forecast to gradually increase over the next 24 hours, and beyond that time, rapidly increase. However, shear should be light enough over the next 12 hours or so to allow a little more intensification of Paula. I will not go as high as the current NHC intensity forecast, however. Instead, I'll go up to 90 kt/105 mph, though it would not be surprising given current trends if Paula has already peaked.
After 24 hours, the shear will increase dramatically, as previously noted, and will also veer from southerly to southwesterly by 36-48 hours, and remain that way throughout the forecast period. This, combined with the likelihood of dry air entrainment from the Gulf of Mexico, along with interaction with the Cuban landmass, suggests that Paula may not even last five days as a tropical cyclone.
In fact, some of the models, including the reliable ECMWF, insist on losing Paula's circulation over the next 1-3 days or have a severely weakened tropical cyclone meandering in the northwest Caribbean Sea for several days, and this is a possible scenario. However, I feel that Paula will maintain enough vertical depth to feel the effects of the trough currently moving across the deep south.
One important development in the synoptic scale steering pattern that has transpired over the last 12 hours or so is that the aforementioned deep-layer trough and accompanying cold front has transitioned from a meridional flow to a more zonal one.
This is evident by analysis of water vapor imagery, mid-level steering from PSU's e-wall, and finally, CIMSS real-time steering data.
This suggests that Paula may move north for a little bit longer than was earlier anticipated, and as a result, I would expect a slight northward shift in the NHC forecast track at 11:00 PM. Nothing drastic, mind you, just a slight northward shift. South Florida is still very likely to avoid a landfall from this storm, and the Florida Keys probably will too. Nevertheless, interests in those areas should still monitor the progress of Paula closely over the next several days.
The current transition to a more zonal flow notwithstanding, Paula should still ultimately miss the US and generally follow the NHC's forecast track, since all of the global models foresee the trough reamplifying over the next day or two as it moves across the southeast United States.
Right now, I agree pretty strongly with the NHC's current forecast track, though I am a little bit further north of it after 24 hours and beyond.
Interests in the Yucatan Peninsula, the Cayman Islands, western and central Cuba, the Florida Keys, south Florida, and the Bahamas should closely follow the progress of Paula over the next several days.
In the meantime, heavy, flooding rains are possible across the eastern portion of the Yucatan Peninsula and western Cuba over the next day or two, along with the likelihood of sustained tropical storm force winds for the former and sustained hurricane force winds for the latter.
The eastern Yucatan Peninsula can expect sustained tropical storm force winds throughout the morning tomorrow, with western Cuba experiencing those winds Wednesday afternoon. Hurricane force sustained winds are likely across western Cuba Wednesday night and into Thursday morning.
Additionally, storm surge flooding will be a serious concern for those areas, as well.
Watches and warnings
A HURRICANE WARNING IS IN EFFECT FOR...
* THE COAST OF MEXICO FROM PUNTA GRUESA NORTHWARD TO CABO CATOCHE...
INCLUDING COZUMEL
* THE PROVINCE OF PINAR DEL RIO CUBA
A TROPICAL STORM WARNING IS IN EFFECT FOR...
* THE COAST OF MEXICO FROM CABO CATOCHE TO SAN FELIPE
Hurricane Paula became a Category 2 hurricane early this afternoon. As of the latest NHC advisory (7:00 PM CDT), here is the latest information on Paula:
Wind: 100 mph, with higher gusts
Movement: N at 9 mph
Pressure: 981 mb
Location: 19.6°N 86.0°W
Category: 2 (Saffir-Simpson Hurricane Wind Scale)
Infrared satellite animations show that Paula is a very small but well-organized hurricane, with a well-defined poleward (north) and equatorial (west) outflow channels due to an amplifying upper trough currently moving across the deep south. However, outflow remains quite restricted to the east, and particularly to the south, due to 20 kt of southerly vertical wind shear analyzed by University of Wisconsin CIMSS. This shear is being induced by a well-defined mid- to upper-level ridge to the east.
An eye is not currently present using conventional satellite imagery, but it was earlier, and all indications are that Paula has maintained her strength over the last couple of hours.
Doppler radar out of Cancun, Mexico shows that Paula has a very small eye, and earlier reconnaissance reports indicates that the eye is no more than, say, 10-15 miles wide. Indeed, if I hadn't been forecasting these systems for three years, I would not, as a layman, be able to readily tell just where Paula's eye is using the aforementioned radar imagery.
I've never seen a Caribbean hurricane as small as Paula, except for perhaps Hurricane Iris in 2001, and even that's iffy since the latter had a larger radius of tropical storm force winds.
Steering analysis from CIMSS indicate that Paula is moving northward under the influence of the aforementioned anticyclone to the east.
Once this shear gets into the core, then rapid weakening is possible, given the hurricane's small size. Shear is forecast to gradually increase over the next 24 hours, and beyond that time, rapidly increase. However, shear should be light enough over the next 12 hours or so to allow a little more intensification of Paula. I will not go as high as the current NHC intensity forecast, however. Instead, I'll go up to 90 kt/105 mph, though it would not be surprising given current trends if Paula has already peaked.
After 24 hours, the shear will increase dramatically, as previously noted, and will also veer from southerly to southwesterly by 36-48 hours, and remain that way throughout the forecast period. This, combined with the likelihood of dry air entrainment from the Gulf of Mexico, along with interaction with the Cuban landmass, suggests that Paula may not even last five days as a tropical cyclone.
In fact, some of the models, including the reliable ECMWF, insist on losing Paula's circulation over the next 1-3 days or have a severely weakened tropical cyclone meandering in the northwest Caribbean Sea for several days, and this is a possible scenario. However, I feel that Paula will maintain enough vertical depth to feel the effects of the trough currently moving across the deep south.
One important development in the synoptic scale steering pattern that has transpired over the last 12 hours or so is that the aforementioned deep-layer trough and accompanying cold front has transitioned from a meridional flow to a more zonal one.
This is evident by analysis of water vapor imagery, mid-level steering from PSU's e-wall, and finally, CIMSS real-time steering data.
This suggests that Paula may move north for a little bit longer than was earlier anticipated, and as a result, I would expect a slight northward shift in the NHC forecast track at 11:00 PM. Nothing drastic, mind you, just a slight northward shift. South Florida is still very likely to avoid a landfall from this storm, and the Florida Keys probably will too. Nevertheless, interests in those areas should still monitor the progress of Paula closely over the next several days.
The current transition to a more zonal flow notwithstanding, Paula should still ultimately miss the US and generally follow the NHC's forecast track, since all of the global models foresee the trough reamplifying over the next day or two as it moves across the southeast United States.
Right now, I agree pretty strongly with the NHC's current forecast track, though I am a little bit further north of it after 24 hours and beyond.
Interests in the Yucatan Peninsula, the Cayman Islands, western and central Cuba, the Florida Keys, south Florida, and the Bahamas should closely follow the progress of Paula over the next several days.
In the meantime, heavy, flooding rains are possible across the eastern portion of the Yucatan Peninsula and western Cuba over the next day or two, along with the likelihood of sustained tropical storm force winds for the former and sustained hurricane force winds for the latter.
The eastern Yucatan Peninsula can expect sustained tropical storm force winds throughout the morning tomorrow, with western Cuba experiencing those winds Wednesday afternoon. Hurricane force sustained winds are likely across western Cuba Wednesday night and into Thursday morning.
Additionally, storm surge flooding will be a serious concern for those areas, as well.
Watches and warnings
A HURRICANE WARNING IS IN EFFECT FOR...
* THE COAST OF MEXICO FROM PUNTA GRUESA NORTHWARD TO CABO CATOCHE...
INCLUDING COZUMEL
* THE PROVINCE OF PINAR DEL RIO CUBA
A TROPICAL STORM WARNING IS IN EFFECT FOR...
* THE COAST OF MEXICO FROM CABO CATOCHE TO SAN FELIPE
Monday, October 11, 2010
Tropical weather analysis - October 11, 2010
Paula
Tropical Storm Paula formed this afternoon in the western Caribbean, east of Honduras. As of the latest NHC advisory (11:00 PM EDT), here is the latest information on Paula:
Wind: 70 mph, with higher gusts
Movement: NW at 10 mph
Pressure: 994 mb
Location: 16.8N 84.6W
Category: Tropical storm
Infrared satellite imagery indicates that Paula is a healthy and intensifying tropical cyclone, with very cold convection over the center and what appears to be the early stages of an eyewall wrapping cyclonically around the center. However, an eye or warm spot is not yet evident using conventional satellite imagery. Unfortunately, there have been no recent microwave satellite passes over the center of the cyclone to confirm this suspicion.
Regardless, it is quite obvious that Paula is an intensifying tropical cyclone. The storm has managed to develop a well-defined poleward and equatorial outflow channel, namely along the northern and western semicircles. Indeed, outflow is also becoming apparent to the south of the center. It remains restricted to the east due to weak southeasterly shear induced by an upper-level high pressure system centered near northwestern Colombia.
Upper-level winds appear favorable for Paula to continue intensifying over at least the next 48 hours. Thereafter, increasing southwesterly to southerly vertical shear will begin to impinge upon the system. This, along with a very dry airmass across the Gulf of Mexico, should begin to weaken Paula after 48 hours. The GFDL brings the system to 75 kt near the northeastern Yucatan Peninsula in 36 hours. While this track seems a tad too fast, the model certainly has the right idea in forecasting such a degree of intensification. In fact, for once, I think the GFDL is being too conservative. I'll go a bit higher, and forecast Paula to become an 85 kt Category 2 hurricane in the western Caribbean in about 48 hours.
It is certainly not out of the question that Paula could become a major hurricane over the next two days or so, especially if current trends continue.
Paula is being steered generally NW by a low- mid-level ridge to the east. It is possible, based on analysis of said imagery along with water vapor imagery, that Paula could turn a little to the right over the next couple hours before bending back to a straight NW course.
In the short-term, Paula should continue moving in this general direction, bringing the center in the general direction of the Yucatan Peninsula in the next 36-48 hours. Thereafter, the track forecast becomes quite complicated, and is dependent entirely upon the strength and amplification of a deep-layer trough forecast by the models to move across the southeast United States.
Depending on the model of your choice, the effects of this trough on Paula's motion varies. Some move the cyclone quickly poleward as Paula comes underneath the influence of the deep-layer westerly flow associated with the aforementioned trough, quickly ejecting it toward western Cuba by about 48 hours.
Others foresee Paula slowing to a crawl and either meandering in the western Caribbean Sea for several days, or moving very slowly eastward, never to leave the Caribbean throughout the forecast period (five days).
Right now, my current thinking is that, based upon current intensification trends and water vapor analysis, Paula will move a bit more poleward than some of the models are thinking, as a well-defined weakness is evident at 400 mb due to a shortwave trough currently moving across the Texas/Louisiana area.
This trough should drop a bit more southward over the next 12-18 hours as a well-defined upper-level low located across the central plains has moved quite far to the southeast over the last several hours. Since Paula is intensifying, it will be strong enough to feel this deep-layer trough. And, as a consequence, move more poleward.
For my forecast track, out of respect for the usual reliability of these two global models, as well as given current trends, and of course, the ever-present uncertainty in long-range weather forecasting, particularly with systems such as Paula, I will compromise between the faster GFS and the slower ECMWF.
This comes out to a forecast of Paula moving NW over the next 36-48 hours, toward the eastern Yucatan Peninsula, and then slowing down a bit and moving very slowly eastward, possibly just north of due E during the remainder of the forecast period.
This track is highly uncertain until the synoptic scale situation becomes clearer. Given the uncertainty, interests in Honduras, Belize, the Yucatan Peninsula, Jamaica, the Cayman Islands, western Cuba, south Florida, and the western Bahamas should closely follow the progress of Paula over the next several days.
In the meantime, heavy rainfall is possible across portions of Honduras, Nicaragua, Jamaica, Belize, the Cayman Islands, the Yucatan Peninsula, and western Cuba over the next several days. These rains have the potential to produce life-threatening flash floods and mudslides across these areas.
Watches and warnings
A HURRICANE WARNING IS IN EFFECT FOR...
* THE COAST OF MEXICO FROM PUNTA GRUESA NORTHWARD TO CABO CATOCHE...
INCLUDING COZUMEL
A TROPICAL STORM WARNING IS IN EFFECT FOR...
* THE COAST OF HONDURAS FROM LIMON EASTWARD TO THE
HONDURAS/NICARAGUA BORDER...INCLUDING THE BAY ISLANDS
* THE COAST OF MEXICO FROM CHETUMAL NORTHWARD TO SOUTH OF PUNTA
GRUESA
* THE COAST OF MEXICO FROM CABO CATOCHE TO SAN FELIPE
A TROPICAL STORM WATCH IS IN EFFECT FOR...
* THE COAST OF BELIZE
Tropical Storm Paula formed this afternoon in the western Caribbean, east of Honduras. As of the latest NHC advisory (11:00 PM EDT), here is the latest information on Paula:
Wind: 70 mph, with higher gusts
Movement: NW at 10 mph
Pressure: 994 mb
Location: 16.8N 84.6W
Category: Tropical storm
Infrared satellite imagery indicates that Paula is a healthy and intensifying tropical cyclone, with very cold convection over the center and what appears to be the early stages of an eyewall wrapping cyclonically around the center. However, an eye or warm spot is not yet evident using conventional satellite imagery. Unfortunately, there have been no recent microwave satellite passes over the center of the cyclone to confirm this suspicion.
Regardless, it is quite obvious that Paula is an intensifying tropical cyclone. The storm has managed to develop a well-defined poleward and equatorial outflow channel, namely along the northern and western semicircles. Indeed, outflow is also becoming apparent to the south of the center. It remains restricted to the east due to weak southeasterly shear induced by an upper-level high pressure system centered near northwestern Colombia.
Upper-level winds appear favorable for Paula to continue intensifying over at least the next 48 hours. Thereafter, increasing southwesterly to southerly vertical shear will begin to impinge upon the system. This, along with a very dry airmass across the Gulf of Mexico, should begin to weaken Paula after 48 hours. The GFDL brings the system to 75 kt near the northeastern Yucatan Peninsula in 36 hours. While this track seems a tad too fast, the model certainly has the right idea in forecasting such a degree of intensification. In fact, for once, I think the GFDL is being too conservative. I'll go a bit higher, and forecast Paula to become an 85 kt Category 2 hurricane in the western Caribbean in about 48 hours.
It is certainly not out of the question that Paula could become a major hurricane over the next two days or so, especially if current trends continue.
Paula is being steered generally NW by a low- mid-level ridge to the east. It is possible, based on analysis of said imagery along with water vapor imagery, that Paula could turn a little to the right over the next couple hours before bending back to a straight NW course.
In the short-term, Paula should continue moving in this general direction, bringing the center in the general direction of the Yucatan Peninsula in the next 36-48 hours. Thereafter, the track forecast becomes quite complicated, and is dependent entirely upon the strength and amplification of a deep-layer trough forecast by the models to move across the southeast United States.
Depending on the model of your choice, the effects of this trough on Paula's motion varies. Some move the cyclone quickly poleward as Paula comes underneath the influence of the deep-layer westerly flow associated with the aforementioned trough, quickly ejecting it toward western Cuba by about 48 hours.
Others foresee Paula slowing to a crawl and either meandering in the western Caribbean Sea for several days, or moving very slowly eastward, never to leave the Caribbean throughout the forecast period (five days).
Right now, my current thinking is that, based upon current intensification trends and water vapor analysis, Paula will move a bit more poleward than some of the models are thinking, as a well-defined weakness is evident at 400 mb due to a shortwave trough currently moving across the Texas/Louisiana area.
This trough should drop a bit more southward over the next 12-18 hours as a well-defined upper-level low located across the central plains has moved quite far to the southeast over the last several hours. Since Paula is intensifying, it will be strong enough to feel this deep-layer trough. And, as a consequence, move more poleward.
For my forecast track, out of respect for the usual reliability of these two global models, as well as given current trends, and of course, the ever-present uncertainty in long-range weather forecasting, particularly with systems such as Paula, I will compromise between the faster GFS and the slower ECMWF.
This comes out to a forecast of Paula moving NW over the next 36-48 hours, toward the eastern Yucatan Peninsula, and then slowing down a bit and moving very slowly eastward, possibly just north of due E during the remainder of the forecast period.
This track is highly uncertain until the synoptic scale situation becomes clearer. Given the uncertainty, interests in Honduras, Belize, the Yucatan Peninsula, Jamaica, the Cayman Islands, western Cuba, south Florida, and the western Bahamas should closely follow the progress of Paula over the next several days.
In the meantime, heavy rainfall is possible across portions of Honduras, Nicaragua, Jamaica, Belize, the Cayman Islands, the Yucatan Peninsula, and western Cuba over the next several days. These rains have the potential to produce life-threatening flash floods and mudslides across these areas.
Watches and warnings
A HURRICANE WARNING IS IN EFFECT FOR...
* THE COAST OF MEXICO FROM PUNTA GRUESA NORTHWARD TO CABO CATOCHE...
INCLUDING COZUMEL
A TROPICAL STORM WARNING IS IN EFFECT FOR...
* THE COAST OF HONDURAS FROM LIMON EASTWARD TO THE
HONDURAS/NICARAGUA BORDER...INCLUDING THE BAY ISLANDS
* THE COAST OF MEXICO FROM CHETUMAL NORTHWARD TO SOUTH OF PUNTA
GRUESA
* THE COAST OF MEXICO FROM CABO CATOCHE TO SAN FELIPE
A TROPICAL STORM WATCH IS IN EFFECT FOR...
* THE COAST OF BELIZE
Saturday, October 9, 2010
Wednesday, October 6, 2010
Tropical weather analysis - October 6, 2010
Otto
Subtropical Storm Otto developed today from what was previously Invest 97L. As of the latest NHC advisory (5:00 PM AST) from the National Hurricane Center, here is the latest information on Otto:
Wind: 60 mph, with higher gusts
Pressure: 990 mb
Movement: N at 5 mph
Location: 23.2°N 68.3°W
Category: Subtropical storm
Infrared satellite loops indicate that Otto may be beginning to acquire tropical characteristics, as an equatorial outflow channel has recently appeared and expanded on the southern side of the storm. This indicates that the system is spreading out warm air in the upper levels, signature of a warm-cored system. Deep convection is also firing closer to the center, but is still located relatively distant from it.
In addition, AMSU temperature profiles from CIMSS and cyclone phase diagrams from FSU suggest that the cyclone is gradually improving its mid- upper-level warm core.
Water vapor imagery indicates that the upper low responsible for Otto's subtropical characteristics is gradually weakening and deamplifying, and is quite elongated at present. Consequently, the surrounding airmass has moistened, indicating less dry mid- to upper-level cold air and more warm moist air. As a result, Otto should gradually acquire tropical characteristics over the next 6-12 hours.
Conditions appear favorable for continued intensification, especially now that the upper low is moving out of the picture. I expect that by morning, Otto will have fully acquired tropical characteristics. There is now a distinct possibility that Otto becomes a hurricane, as most of the models are reflecting this. I agree rather well with the NHC's current intensity forecast:
FORECAST POSITIONS AND MAX WINDS
INITIAL 06/2100Z 23.2N 68.3W 50 KT
12HR VT 07/0600Z 23.8N 68.5W 55 KT
24HR VT 07/1800Z 24.5N 67.9W 60 KT
36HR VT 08/0600Z 25.5N 66.4W 65 KT
48HR VT 08/1800Z 26.8N 63.7W 65 KT
72HR VT 09/1800Z 30.3N 55.8W 55 KT
96HR VT 10/1800Z 34.5N 44.5W 40 KT...POST-TROP/EXTRATROP
120HR VT 11/1800Z 39.0N 31.0W 35 KT...POST-TROP/EXTRATROP
$$
FORECASTER STEWART
Otto is forecast to be extratropical in about four days as it interacts with a large and powerful baroclinic system to the west.
Otto is located in a weak steering regime between a well-defined and slow-moving longwave trough to the west and the subtropical ridge to the east. Such a steering pattern favors a continued slow generally N motion over the next 18-24 hours, though there could be some wobbles to the NW during this time as well. Thereafter, the global models unanimously predict a gradual acceleration to the NE as Otto becomes well-embedded within the southwesterly steering regime associated with the aforementioned trough, which is forecast to move closer to Otto over the next day or so.
In about two and a half to three days, the models diverge, with some accelerating Otto more NNE, with others accelerating him ENE. I still feel the trough is amplified enough to bring Otto along the eastern edge of the guidance envelope. The HWRF, UKMET, and ECMWF models are on the western edge of the guidance, forecasting Otto to move well west of the Azores. I tend to favor the more eastern camp, composed of the NGFDL, GFDL, and GFS models.
I am unsure what is causing the GFS to move Otto sharply east near the end of the forecast period, and so I will discount that solution for now. My forecast track takes Otto within 100 miles west of the western end of the Azores in about five days, and interests there should closely follow the progress of this system.
Last night I had mentioned the possibility that Otto could become absorbed into a large extratropical low pressure system over the next few days, but this solution now appears unlikely. While interaction with this low will ultimately cause Otto to transition into an extratropical storm, global models suggest that Otto will remain a separate entity, distinct from the aforementioned baroclinic low throughout the forecast period.
Because Otto will be extratropical as it approaches the Azores, impacts will be felt well away from the center, particularly to the northeast. Hence, the center of the cyclone should not be focused on in this instance. Otto could also ultimately impact western Europe sometime next week.
Elsewhere
Elsewhere in the tropics, several of the global models continue to indicate the possibility of tropical cyclogenesis in the southwestern Caribbean in the next 5-7 days. However, they have become less aggressive today. If this becomes an established trend, it may mean that this system will not become as strong as previously thought. This possibility will have to be carefully assessed over the next few days.
The exact details of the track are uncertain, but right now I'd expect a track similar to Nicole.
Subtropical Storm Otto developed today from what was previously Invest 97L. As of the latest NHC advisory (5:00 PM AST) from the National Hurricane Center, here is the latest information on Otto:
Wind: 60 mph, with higher gusts
Pressure: 990 mb
Movement: N at 5 mph
Location: 23.2°N 68.3°W
Category: Subtropical storm
Infrared satellite loops indicate that Otto may be beginning to acquire tropical characteristics, as an equatorial outflow channel has recently appeared and expanded on the southern side of the storm. This indicates that the system is spreading out warm air in the upper levels, signature of a warm-cored system. Deep convection is also firing closer to the center, but is still located relatively distant from it.
In addition, AMSU temperature profiles from CIMSS and cyclone phase diagrams from FSU suggest that the cyclone is gradually improving its mid- upper-level warm core.
Water vapor imagery indicates that the upper low responsible for Otto's subtropical characteristics is gradually weakening and deamplifying, and is quite elongated at present. Consequently, the surrounding airmass has moistened, indicating less dry mid- to upper-level cold air and more warm moist air. As a result, Otto should gradually acquire tropical characteristics over the next 6-12 hours.
Conditions appear favorable for continued intensification, especially now that the upper low is moving out of the picture. I expect that by morning, Otto will have fully acquired tropical characteristics. There is now a distinct possibility that Otto becomes a hurricane, as most of the models are reflecting this. I agree rather well with the NHC's current intensity forecast:
FORECAST POSITIONS AND MAX WINDS
INITIAL 06/2100Z 23.2N 68.3W 50 KT
12HR VT 07/0600Z 23.8N 68.5W 55 KT
24HR VT 07/1800Z 24.5N 67.9W 60 KT
36HR VT 08/0600Z 25.5N 66.4W 65 KT
48HR VT 08/1800Z 26.8N 63.7W 65 KT
72HR VT 09/1800Z 30.3N 55.8W 55 KT
96HR VT 10/1800Z 34.5N 44.5W 40 KT...POST-TROP/EXTRATROP
120HR VT 11/1800Z 39.0N 31.0W 35 KT...POST-TROP/EXTRATROP
$$
FORECASTER STEWART
Otto is forecast to be extratropical in about four days as it interacts with a large and powerful baroclinic system to the west.
Otto is located in a weak steering regime between a well-defined and slow-moving longwave trough to the west and the subtropical ridge to the east. Such a steering pattern favors a continued slow generally N motion over the next 18-24 hours, though there could be some wobbles to the NW during this time as well. Thereafter, the global models unanimously predict a gradual acceleration to the NE as Otto becomes well-embedded within the southwesterly steering regime associated with the aforementioned trough, which is forecast to move closer to Otto over the next day or so.
In about two and a half to three days, the models diverge, with some accelerating Otto more NNE, with others accelerating him ENE. I still feel the trough is amplified enough to bring Otto along the eastern edge of the guidance envelope. The HWRF, UKMET, and ECMWF models are on the western edge of the guidance, forecasting Otto to move well west of the Azores. I tend to favor the more eastern camp, composed of the NGFDL, GFDL, and GFS models.
I am unsure what is causing the GFS to move Otto sharply east near the end of the forecast period, and so I will discount that solution for now. My forecast track takes Otto within 100 miles west of the western end of the Azores in about five days, and interests there should closely follow the progress of this system.
Last night I had mentioned the possibility that Otto could become absorbed into a large extratropical low pressure system over the next few days, but this solution now appears unlikely. While interaction with this low will ultimately cause Otto to transition into an extratropical storm, global models suggest that Otto will remain a separate entity, distinct from the aforementioned baroclinic low throughout the forecast period.
Because Otto will be extratropical as it approaches the Azores, impacts will be felt well away from the center, particularly to the northeast. Hence, the center of the cyclone should not be focused on in this instance. Otto could also ultimately impact western Europe sometime next week.
Elsewhere
Elsewhere in the tropics, several of the global models continue to indicate the possibility of tropical cyclogenesis in the southwestern Caribbean in the next 5-7 days. However, they have become less aggressive today. If this becomes an established trend, it may mean that this system will not become as strong as previously thought. This possibility will have to be carefully assessed over the next few days.
The exact details of the track are uncertain, but right now I'd expect a track similar to Nicole.
Tuesday, October 5, 2010
Tropical weather analysis - October 5,, 2010
Invest 97L
An area of low pressure, located just north of Puerto Rico, dubbed "Invest 97L" by the National Hurricane Center, is producing a large and elongated area of showers and thunderstorms to the north and east of the estimated center. Analysis of shortwave infrared satellite imagery, buoy observations, and various other data indicate that the system does not yet have a well-defined surface circulation. However, the low-level center appears to be gradually becoming better-defined, as noted by low-cloud motions observed on satellite imagery.
The center appears to be located near 22N 66W according to the various data I've been able to analyze.
Infrared satellite imagery shows that 97L is still disorganized, but the convective bands to the north and east of the center appear to be becoming a bit more collocated with the center, a sign of increasing organization.
CIMSS analysis depicts 20 kt of westerly vertical shear blowing just to the north of the circulation center. This shear is responsible for the current subtropical appearance of the storm on satellite.
In addition, water vapor imagery shows that a large area of dry air surrounds 97L, and its counter-clockwise circulation is acting to pull in some of this dry air, which is also inhibiting any appreciable convective activity from developing and persisting near the center.
AMSU data from CIMSS along with cyclone phase diagrams from FSU indicate that the system currently lacks a well-defined warm core, with only a shallow warm core at best noted in the imagery.
Nevertheless, 97L appears to be gradually acquiring subtropical characteristics, and this system could become a subtropical cyclone at any time over the next 12-18 hours.
Based on the various steering data I've analyzed, I expect 97L to move NNW to NW over the next 36 hours or so with a gradual decrease in forward speed. Thereafter, the models unanimously forecast a stall as a well-defined longwave trough currently over the western Atlantic moves eastward and weakens the steering currents. After 48 hours, steering currents will once again become well-established as 97L/Otto becomes well-embedded within the southwesterly steering regime of said trough.
As a consequence, 97L can be expected to move NNE to ENE with a gradual acceleration after 48 hours. The models are split in their respective tracks. While it's impossible to tell at this juncture which camp of models is correct, I'll go with the easternmost camp, comprised of the NOGAPS and GFDL models, which would eventually bring the system near the western end of the Azores. This is based on the amplification of the aforementioned trough, which I feel will be quite significant.
By day four, the models forecast 97L/Otto to lose tropical characteristics (or subtropical characteristics) and become extratropical as it interacts with a large baroclinic system associated with the western Atlantic trough. 97L should ultimately become absorbed into this low, potentially impacting western Europe in about 7 days.
Vertical shear is gradually easing, and is forecast to lessen further over the next couple of days. In fact, the 18z GFS suggests that a weakly anticyclonic environment will develop over the system during the next day or so, and persist until 48 hours. Any potential transition to a tropical cyclone will occur then, when the trough will be relatively distant from the center and the anticyclone (high pressure ridge) established aloft, pumping warm air into the system at the upper-levels.
I do expect 97L to make the transition to a fully tropical cyclone sometime over the next 36 hours.
By 48 hours, vertical shear is forecast to increase sharply as the trough and associated cold front moves closer to the system. It is at this point that the system will lose its anticyclone.
It is possible that 97L becomes a hurricane, but this looks highly unlikely.
Elsewhere
Elsewhere in the tropics, the GFS, ECMWF, and NOGAPS forecast the development of a tropical depression in the western Caribbean Sea in about 5-7 days. The eventual path of such a system is uncertain.
An area of low pressure, located just north of Puerto Rico, dubbed "Invest 97L" by the National Hurricane Center, is producing a large and elongated area of showers and thunderstorms to the north and east of the estimated center. Analysis of shortwave infrared satellite imagery, buoy observations, and various other data indicate that the system does not yet have a well-defined surface circulation. However, the low-level center appears to be gradually becoming better-defined, as noted by low-cloud motions observed on satellite imagery.
The center appears to be located near 22N 66W according to the various data I've been able to analyze.
Infrared satellite imagery shows that 97L is still disorganized, but the convective bands to the north and east of the center appear to be becoming a bit more collocated with the center, a sign of increasing organization.
CIMSS analysis depicts 20 kt of westerly vertical shear blowing just to the north of the circulation center. This shear is responsible for the current subtropical appearance of the storm on satellite.
In addition, water vapor imagery shows that a large area of dry air surrounds 97L, and its counter-clockwise circulation is acting to pull in some of this dry air, which is also inhibiting any appreciable convective activity from developing and persisting near the center.
AMSU data from CIMSS along with cyclone phase diagrams from FSU indicate that the system currently lacks a well-defined warm core, with only a shallow warm core at best noted in the imagery.
Nevertheless, 97L appears to be gradually acquiring subtropical characteristics, and this system could become a subtropical cyclone at any time over the next 12-18 hours.
Based on the various steering data I've analyzed, I expect 97L to move NNW to NW over the next 36 hours or so with a gradual decrease in forward speed. Thereafter, the models unanimously forecast a stall as a well-defined longwave trough currently over the western Atlantic moves eastward and weakens the steering currents. After 48 hours, steering currents will once again become well-established as 97L/Otto becomes well-embedded within the southwesterly steering regime of said trough.
As a consequence, 97L can be expected to move NNE to ENE with a gradual acceleration after 48 hours. The models are split in their respective tracks. While it's impossible to tell at this juncture which camp of models is correct, I'll go with the easternmost camp, comprised of the NOGAPS and GFDL models, which would eventually bring the system near the western end of the Azores. This is based on the amplification of the aforementioned trough, which I feel will be quite significant.
By day four, the models forecast 97L/Otto to lose tropical characteristics (or subtropical characteristics) and become extratropical as it interacts with a large baroclinic system associated with the western Atlantic trough. 97L should ultimately become absorbed into this low, potentially impacting western Europe in about 7 days.
Vertical shear is gradually easing, and is forecast to lessen further over the next couple of days. In fact, the 18z GFS suggests that a weakly anticyclonic environment will develop over the system during the next day or so, and persist until 48 hours. Any potential transition to a tropical cyclone will occur then, when the trough will be relatively distant from the center and the anticyclone (high pressure ridge) established aloft, pumping warm air into the system at the upper-levels.
I do expect 97L to make the transition to a fully tropical cyclone sometime over the next 36 hours.
By 48 hours, vertical shear is forecast to increase sharply as the trough and associated cold front moves closer to the system. It is at this point that the system will lose its anticyclone.
It is possible that 97L becomes a hurricane, but this looks highly unlikely.
Elsewhere
Elsewhere in the tropics, the GFS, ECMWF, and NOGAPS forecast the development of a tropical depression in the western Caribbean Sea in about 5-7 days. The eventual path of such a system is uncertain.
Tuesday, August 24, 2010
Tropical weather analysis - August 24, 2010
Danielle
Danielle, after a period of rapid intensification yesterday afternoon and evening, has weakened just as quickly today, dropping below hurricane status as of the 5:00 PM EDT advisory from the National Hurricane Center. Speaking of the 5:00 PM advisory, here is the information they put out during that time:
Wind: 70 mph, with higher gusts
Pressure: 993 mb
Movement: WNW at 18 mph
Location: 17.5°N 48.2°W
Category: Tropical storm
The last of the visible satellite imagery along with animation of shortwave infrared imagery, suggest that the cyclone is once again becoming better organized, with the center now pretty much fully underneath the steadily increasing deep convection.
Additionally, a recent SSMI/S microwave satellite overpass, along with CIMSS vorticity analysis indicates that the low- and mid-level centers are fairly well aligned in the vertical, with only perhaps a very slight eastward decoupling of the centers. More importantly, the aforementioned SSMI/S overpass suggests that Danielle is in the process of reforming an eye and eyewall, though the former is not currently visible on satellite imagery.
Danielle is currently experiencing about 10 knots of westerly vertical wind shear. It appears that over the last 18 hours, the well-defined 200 mb anticyclone, observed on the link above, has detached from the circulation of Danielle, and, rather than aiding it, it has been shearing it. Additionally, wind shear has decreased over the system the last six hours.
Based on all of this, Danielle's weakening throughout the day should be relatively short-lived, and I expect she will reattain hurricane status by the time of the next advisory. And if not at that time, definitely at the 5:00 AM one. Based on the 18z GFS, the anticyclone should become reestablished over the storm in about 18-24 hours, so I expect some more steady intensification to begin tomorrow evening, and into Thursday morning. Shear could increase again during the 72-96 hour time frame, as the cyclone comes underneath the influences of upper southwesterlies associated with a longwave trough currently moving across the central and southern United States. However, this shear may not be quite as detrimental as one would expect if Danielle moves more NE with acceleration, as it will be moving in the same direction as the shear vector.
As far as track is concerned, I expect that, based on water vapor animations, CIMSS steering data, and 0z steering data from PSU's e-wall, Danielle will continue to track more westerly (specifically, WNW, though a slight W motion cannot be ruled out at this time, either) for the next 12 hours or so, as the weakness in the ridge evident on water vapor imagery and steering data from CIMSS to the north of her, along 25N from 50 to 45W, doesn't appear to be appreciably affecting the cyclone just yet.
My forecast track is a blend of the 18z GFS and 12z CMC, which calls for a continued WNW motion for the next 12 hours or so, followed by a NW turn and an associated decrease in forward speed as the system approaches the aforementioned weakness. This general motion, albeit with some possible oscillations to the left or right, should continue through at least day three. Thereafter, models diverge, with some turning Danielle N quicker, and some slower. The GFS, in a sharp contrast from what it has been doing the past several days, foresees a sharp westward turn near the end of the forecast period, which could potentially mean a landfall in the mid-Atlantic or New England in about seven days. However, I will not go that far west at this time, since the models have the luxury of flipflopping at random, while I am forced to remain consistent.
All in all, I expect a NW to begin in about 12 hours, and this should persist until around 108 hours, at which point a turn to the N is likely. However, given that the usual uncertainty in long-range forecasts, as well as the fact that the GFS trended westward at 18z, and the 12z NOGAPS tracks the center directly over Bermuda at day five, interests in Bermuda should closely follow the progress of Danielle over the next several days.
The tropical storm force wind probability map from the National Hurricane Center indicates that there is a 30% chance of Bermuda receiving tropical storm force winds from Danielle over the next five days, and that island is not out of the woods by any means. I still suspect Danielle will pass east of Bermuda, but this is not certain, and it could come closer to the island than I was thinking last night.
Interests along the mid-Atlantic and New England coasts should also be monitoring Danielle, as should Atlantic Canada.
Invest 96L
A strong tropical wave, "Invest 96L", is located near 13N (nearing 14N) 26W. This system continues to display signs of organization on satellite imagery, though deep convection is currently minimal, and a bit to the west of the 850 mb vorticity maximum.
CIMSS shear data indicates that this system is experiencing 20 knots of southwesterly shear. However, there are no apparent signs of this shear on satellite imagery. The likely catalyst for the recent wane in convection is some slight dry entrainment noted on water vapor imagery. This dry air is associated with a pocket of Saharan Air Layer (SAL) located to the west of 96L.
The dry air notwithstanding, conditions appear favorable for continued slow development over the next couple of days, and this system could become a tropical depression during the next couple of days. The GFS suggests that this will develop in just about 12 hours. I suspect it will take a little more time than that, based on current trends and forecast shear from the GFS. Instead, I expect this will undergo tropical cyclogenesis in about 18 to 24 hours. If dry air continues to hinder this system, however, it could take even longer. It should be noted that the models have shifted considerably southward today, and now foresee 96L being a long-range threat to the southeast United States.
The weaker it stays, the more southerly it should go. Given that the system will be passing over the cold water wake generated by Danielle, it should remain below hurricane status until around day four. None of the models, save the GFS, show this system becoming a hurricane during the next five days. I tend to agree with the models on the track, and the United States may not be so lucky with this one.
Elsewhere
Elsewhere, showers and thunderstorms across the central Gulf of Mexico are associated with a surface trough. This system is currently very poorly organized, and any development should be slow to occur as the system moves W at 5 to 10 mph over the next several days. A turn to the NW could occur on day three as the ridge weakens somewhat. Residents from northeast Mexico to the upper Texas coast should closely monitor the progress of this system over the next several days. I am not really expecting development here, and none of the models show it either.
The 18z GFS is forecasting that a third tropical cyclone will develop behind Danielle and future Earl late on day five. This is a sign that the tropics are heating up, and residents in hurricane prone areas should review their preparedness plans. We're still likely to churn out at least 15 storms this season, and it's not over by a longshot.
Danielle, after a period of rapid intensification yesterday afternoon and evening, has weakened just as quickly today, dropping below hurricane status as of the 5:00 PM EDT advisory from the National Hurricane Center. Speaking of the 5:00 PM advisory, here is the information they put out during that time:
Wind: 70 mph, with higher gusts
Pressure: 993 mb
Movement: WNW at 18 mph
Location: 17.5°N 48.2°W
Category: Tropical storm
The last of the visible satellite imagery along with animation of shortwave infrared imagery, suggest that the cyclone is once again becoming better organized, with the center now pretty much fully underneath the steadily increasing deep convection.
Additionally, a recent SSMI/S microwave satellite overpass, along with CIMSS vorticity analysis indicates that the low- and mid-level centers are fairly well aligned in the vertical, with only perhaps a very slight eastward decoupling of the centers. More importantly, the aforementioned SSMI/S overpass suggests that Danielle is in the process of reforming an eye and eyewall, though the former is not currently visible on satellite imagery.
Danielle is currently experiencing about 10 knots of westerly vertical wind shear. It appears that over the last 18 hours, the well-defined 200 mb anticyclone, observed on the link above, has detached from the circulation of Danielle, and, rather than aiding it, it has been shearing it. Additionally, wind shear has decreased over the system the last six hours.
Based on all of this, Danielle's weakening throughout the day should be relatively short-lived, and I expect she will reattain hurricane status by the time of the next advisory. And if not at that time, definitely at the 5:00 AM one. Based on the 18z GFS, the anticyclone should become reestablished over the storm in about 18-24 hours, so I expect some more steady intensification to begin tomorrow evening, and into Thursday morning. Shear could increase again during the 72-96 hour time frame, as the cyclone comes underneath the influences of upper southwesterlies associated with a longwave trough currently moving across the central and southern United States. However, this shear may not be quite as detrimental as one would expect if Danielle moves more NE with acceleration, as it will be moving in the same direction as the shear vector.
As far as track is concerned, I expect that, based on water vapor animations, CIMSS steering data, and 0z steering data from PSU's e-wall, Danielle will continue to track more westerly (specifically, WNW, though a slight W motion cannot be ruled out at this time, either) for the next 12 hours or so, as the weakness in the ridge evident on water vapor imagery and steering data from CIMSS to the north of her, along 25N from 50 to 45W, doesn't appear to be appreciably affecting the cyclone just yet.
My forecast track is a blend of the 18z GFS and 12z CMC, which calls for a continued WNW motion for the next 12 hours or so, followed by a NW turn and an associated decrease in forward speed as the system approaches the aforementioned weakness. This general motion, albeit with some possible oscillations to the left or right, should continue through at least day three. Thereafter, models diverge, with some turning Danielle N quicker, and some slower. The GFS, in a sharp contrast from what it has been doing the past several days, foresees a sharp westward turn near the end of the forecast period, which could potentially mean a landfall in the mid-Atlantic or New England in about seven days. However, I will not go that far west at this time, since the models have the luxury of flipflopping at random, while I am forced to remain consistent.
All in all, I expect a NW to begin in about 12 hours, and this should persist until around 108 hours, at which point a turn to the N is likely. However, given that the usual uncertainty in long-range forecasts, as well as the fact that the GFS trended westward at 18z, and the 12z NOGAPS tracks the center directly over Bermuda at day five, interests in Bermuda should closely follow the progress of Danielle over the next several days.
The tropical storm force wind probability map from the National Hurricane Center indicates that there is a 30% chance of Bermuda receiving tropical storm force winds from Danielle over the next five days, and that island is not out of the woods by any means. I still suspect Danielle will pass east of Bermuda, but this is not certain, and it could come closer to the island than I was thinking last night.
Interests along the mid-Atlantic and New England coasts should also be monitoring Danielle, as should Atlantic Canada.
Invest 96L
A strong tropical wave, "Invest 96L", is located near 13N (nearing 14N) 26W. This system continues to display signs of organization on satellite imagery, though deep convection is currently minimal, and a bit to the west of the 850 mb vorticity maximum.
CIMSS shear data indicates that this system is experiencing 20 knots of southwesterly shear. However, there are no apparent signs of this shear on satellite imagery. The likely catalyst for the recent wane in convection is some slight dry entrainment noted on water vapor imagery. This dry air is associated with a pocket of Saharan Air Layer (SAL) located to the west of 96L.
The dry air notwithstanding, conditions appear favorable for continued slow development over the next couple of days, and this system could become a tropical depression during the next couple of days. The GFS suggests that this will develop in just about 12 hours. I suspect it will take a little more time than that, based on current trends and forecast shear from the GFS. Instead, I expect this will undergo tropical cyclogenesis in about 18 to 24 hours. If dry air continues to hinder this system, however, it could take even longer. It should be noted that the models have shifted considerably southward today, and now foresee 96L being a long-range threat to the southeast United States.
The weaker it stays, the more southerly it should go. Given that the system will be passing over the cold water wake generated by Danielle, it should remain below hurricane status until around day four. None of the models, save the GFS, show this system becoming a hurricane during the next five days. I tend to agree with the models on the track, and the United States may not be so lucky with this one.
Elsewhere
Elsewhere, showers and thunderstorms across the central Gulf of Mexico are associated with a surface trough. This system is currently very poorly organized, and any development should be slow to occur as the system moves W at 5 to 10 mph over the next several days. A turn to the NW could occur on day three as the ridge weakens somewhat. Residents from northeast Mexico to the upper Texas coast should closely monitor the progress of this system over the next several days. I am not really expecting development here, and none of the models show it either.
The 18z GFS is forecasting that a third tropical cyclone will develop behind Danielle and future Earl late on day five. This is a sign that the tropics are heating up, and residents in hurricane prone areas should review their preparedness plans. We're still likely to churn out at least 15 storms this season, and it's not over by a longshot.
Monday, August 23, 2010
Tropical weather analysis - August 23, 2010
Danielle
Hurricane Danielle continues to churn in the central Atlantic Ocean, and is located between Africa and the Lesser Antilles. Here is the latest information put out by the National Hurricane Center at the 11:00 PM EDT advisory:
Wind: 85 mph, with higher gusts
Pressure: 982 mb
Movement: WNW at 20 mph
Location: 15.6°N 43.2°W
Category: 1 (Saffir-Simpson Hurricane Wind Scale)
The hurricane appears to be steadily organizing, with infrared satellite loops indicating a well-defined central dense overcast (CDO), alongside a developing eye.
However, Danielle appears to be battling some slight dry air on its western periphery, as evidenced by water vapor loops. However, recent convective trends seem to indicate that perhaps the hurricane is managing to gradually mix out the aforementioned dry air. We'll see if this continues. Either way, only a gradual intensification is to be expected tonight, and Danielle should not reach Category 2 status until tomorrow morning, depending on how well she does against the dry air. This dry air will not be enough to weaken her, however, so that should definitely be remembered.
Danielle also has a well-organized structure aloft, with a recent SSMI/S microwave pass indicating a closed eyewall and gradually clearing eye aloft.
Upper-tropospheric outflow is well-defined both poleward and equatorial, but restricted along the western side, owing to the dry air. I suspect that dry air will continue to limit outflow in that direction for at least the next 12 hours.
All in all, based on everything I've analyzed, I believe that Danielle will continue to steadily intensify over the next 24-30 hours, as an an upper-level anticyclone moves more or less in tandem with the system. Thereafter, southwesterly shear is forecast to increase as a secondary trough, a weaker one currently in the vicinity of the east coast/western Atlantic moves eastward and impinges upon the hurricane. This should slow intensification beyond that time, but will probably not be enough to effectively prevent it, as I still feel the GFS is overdoing the shear, based on the current strength of the aforementioned trough. The 18z GFDL generally agrees with my thinking, and foresees that Danielle will be a steady state hurricane from 36-60 hours, after which point it will have a brief, 12 hour window of opportunity to strength to a major hurricane. The GFDL brings this up to 107 knots, and this is certainly possible.
I'll go slightly higher, however, and forecast a 110 knot hurricane, which is a hurricane with winds of 125 mph.
The track forecast for Danielle has, fortunately, become much simpler this evening. The models now unanimously agree upon a highly amplified upper air pattern fully recurving the hurricane out to sea. Indeed, even the NOGAPS, which has had an equatorial bias with this storm, has joined the recurvature crew.
Current model trends suggest that Danielle will pass well to the east of Bermuda, by about 150 to 200 miles, on day five. However, given some uncertainties in the evolution of a well-defined upper-level trough currently moving across the central plains and midwestern states, interests in Bermuda should closely monitor the progress of this system. Interests in eastern Atlantic Canada should also follow the progress of Danielle over the next several days, even though at this moment it appears that a landfall will not occur there (same with Bermuda). My track forecast is in best agreement with the 18z GFDL.
Invest 96L
A well-defined, convectively active tropical wave, is located in the far eastern Atlantic Ocean, about 150 miles south of the Cape Verde Islands. This wave was dubbed "Invest 96L" by the National Hurricane Center this afternoon. This system certainly has the potential to become the season's next named storm over the next couple of days.
Infrared satellite loops suggest that, while convection had waned in recent hours, it is making something of a comeback now. However, CIMSS 850 mb vorticity data suggests that the system still needs to tighten up its low-level circulation, which will take some time. However, conditions appear favorable for some slow additional development of this system as it moves W to WNW over the next couple of days, at around 15 to 20 mph.
Most the models, save the GFDL and NOGAPS, which does not develop it, make this system a tropical cyclone anywhere between tomorrow morning and Wednesday morning. Shear is forecast to be favorable for intensification of the system throughout much of the forecast period, with an upper-level anticyclone forecast to move roughly in tandem with the system.
The 18z HWRF makes this system a hurricane in four days, and more intensification should be expected during the three to four day time frame, so this possibility cannot be discounted. At this time, I do see this system being named, probably by Wednesday morning.
The track of 96L is much more uncertain than it is with Danielle. Some models forecast recurvature, while others forecast a more westward motion, toward the southeast United States coast. I'll split the difference out of respect for the models, but I still think they are overdoing the weakness in the ridge, and the amplification of the upper pattern. This is one to watch, if the equatorial shift we observed in the models earlier continues to occur.
Hurricane Danielle continues to churn in the central Atlantic Ocean, and is located between Africa and the Lesser Antilles. Here is the latest information put out by the National Hurricane Center at the 11:00 PM EDT advisory:
Wind: 85 mph, with higher gusts
Pressure: 982 mb
Movement: WNW at 20 mph
Location: 15.6°N 43.2°W
Category: 1 (Saffir-Simpson Hurricane Wind Scale)
The hurricane appears to be steadily organizing, with infrared satellite loops indicating a well-defined central dense overcast (CDO), alongside a developing eye.
However, Danielle appears to be battling some slight dry air on its western periphery, as evidenced by water vapor loops. However, recent convective trends seem to indicate that perhaps the hurricane is managing to gradually mix out the aforementioned dry air. We'll see if this continues. Either way, only a gradual intensification is to be expected tonight, and Danielle should not reach Category 2 status until tomorrow morning, depending on how well she does against the dry air. This dry air will not be enough to weaken her, however, so that should definitely be remembered.
Danielle also has a well-organized structure aloft, with a recent SSMI/S microwave pass indicating a closed eyewall and gradually clearing eye aloft.
Upper-tropospheric outflow is well-defined both poleward and equatorial, but restricted along the western side, owing to the dry air. I suspect that dry air will continue to limit outflow in that direction for at least the next 12 hours.
All in all, based on everything I've analyzed, I believe that Danielle will continue to steadily intensify over the next 24-30 hours, as an an upper-level anticyclone moves more or less in tandem with the system. Thereafter, southwesterly shear is forecast to increase as a secondary trough, a weaker one currently in the vicinity of the east coast/western Atlantic moves eastward and impinges upon the hurricane. This should slow intensification beyond that time, but will probably not be enough to effectively prevent it, as I still feel the GFS is overdoing the shear, based on the current strength of the aforementioned trough. The 18z GFDL generally agrees with my thinking, and foresees that Danielle will be a steady state hurricane from 36-60 hours, after which point it will have a brief, 12 hour window of opportunity to strength to a major hurricane. The GFDL brings this up to 107 knots, and this is certainly possible.
I'll go slightly higher, however, and forecast a 110 knot hurricane, which is a hurricane with winds of 125 mph.
The track forecast for Danielle has, fortunately, become much simpler this evening. The models now unanimously agree upon a highly amplified upper air pattern fully recurving the hurricane out to sea. Indeed, even the NOGAPS, which has had an equatorial bias with this storm, has joined the recurvature crew.
Current model trends suggest that Danielle will pass well to the east of Bermuda, by about 150 to 200 miles, on day five. However, given some uncertainties in the evolution of a well-defined upper-level trough currently moving across the central plains and midwestern states, interests in Bermuda should closely monitor the progress of this system. Interests in eastern Atlantic Canada should also follow the progress of Danielle over the next several days, even though at this moment it appears that a landfall will not occur there (same with Bermuda). My track forecast is in best agreement with the 18z GFDL.
Invest 96L
A well-defined, convectively active tropical wave, is located in the far eastern Atlantic Ocean, about 150 miles south of the Cape Verde Islands. This wave was dubbed "Invest 96L" by the National Hurricane Center this afternoon. This system certainly has the potential to become the season's next named storm over the next couple of days.
Infrared satellite loops suggest that, while convection had waned in recent hours, it is making something of a comeback now. However, CIMSS 850 mb vorticity data suggests that the system still needs to tighten up its low-level circulation, which will take some time. However, conditions appear favorable for some slow additional development of this system as it moves W to WNW over the next couple of days, at around 15 to 20 mph.
Most the models, save the GFDL and NOGAPS, which does not develop it, make this system a tropical cyclone anywhere between tomorrow morning and Wednesday morning. Shear is forecast to be favorable for intensification of the system throughout much of the forecast period, with an upper-level anticyclone forecast to move roughly in tandem with the system.
The 18z HWRF makes this system a hurricane in four days, and more intensification should be expected during the three to four day time frame, so this possibility cannot be discounted. At this time, I do see this system being named, probably by Wednesday morning.
The track of 96L is much more uncertain than it is with Danielle. Some models forecast recurvature, while others forecast a more westward motion, toward the southeast United States coast. I'll split the difference out of respect for the models, but I still think they are overdoing the weakness in the ridge, and the amplification of the upper pattern. This is one to watch, if the equatorial shift we observed in the models earlier continues to occur.
Sunday, August 22, 2010
Tropical weather analysis - August 22, 2010
Danielle
Tropical Storm Danielle has formed today in the eastern Atlantic Ocean several hundred miles west of the Cape Verde Islands. Here is the latest information from the National Hurricane Center, released at 5:00 PM EDT:
Maximum sustained winds: 50 mph, with higher gusts
Minimum central pressure: 1000 mb
Movement: NW at 13 mph
Location: 14.2°N 35.9°W
Shortwave infrared satellite images suggest that the circulation center is almost completely tucked underneath the large mass of very deep convection, but is very slightly exposed to the east. In fact, cloud tops are as cold as -90°C near the middle of the large convective ball.
There is still no evidence of upper-level outflow in the eastern semicircle, due to the continuance of strong easterly shear, analyzed as high as 30 knots by data from the University of Wisconsin's CIMSS. However, given current organizational trends on satellite imagery, I do not believe that the shear is as strong as is being analyzed by CIMSS. This shear is being induced in part by a large and complex area of disturbed weather several hundred miles to the east of Danielle, which some models forecast will become the season's next tropical depression over the next several days, and also partly by an intensifying upper-level anticyclone centered to the north of Danielle.
The cyclone currently appears to be moving NW, based on low cloud motions observed on satellite imagery. However, water vapor animations and 500 mb steering data from CIMSS suggest that this is merely a temporary motion, albeit pronounced, and Danielle should resume a WNW track over the next 6-12 hours. And based on water vapor imagery, a due W motion is even possible as Danielle nears 45W. But this will depend upon how the subtropical ridge evolves over the coming days. But this is a possibility that needs to be carefully assessed.
Based on water vapor animations and various other steering data, I strongly believe that the models are overdoing the trough and the consequent weakness in the Atlantic subtropical ridge. The culprit for potential recurvature that the models are seeing is a vigorous mid- to upper-level trough currently centered across the west-central United States. Though it cannot be said with absolute certainty at this juncture, it is quite possible that this trough will emerge too far north to completely recurve Danielle.
All of the models unanimously agree on Danielle moving generally WNW for the next 72 hours or so with a gradual increase in forward speed, after which point the subtropical ridge is forecast to reveal a weakness from 60 to 70W as the aforementioned trough emerges from the mid-Atlantic or New England. At that point, a gradual deceleration can be expected, and Danielle will likely turn NW after 72 hours, and could turn N by day four or five. However, this is becoming less likely. Instead, a slow NW motion should be expected by that time.
Beyond 120 hours, most of the models show a reestablishment of the subtropical ridge to the north of the system, which would tend to favor a more W track at the end of the forecast period. So for now, I agree with the NHC's current forecast track, given the strong uncertainty, greater than usual, in the forecast track.
The intensity forecast, thankfully, is much easier. The currently easterly shear should abate by tomorrow as the aforementioned anticyclone becomes more collocated with Danielle. It should then move in tandem with the cyclone for the next three days, providing a low shear environment favorable for strengthening. After 72 hours, southwesterly shear is forecast to increase as Danielle encounters an upper low currently centered in the central Atlantic Ocean. However, I feel the GFS may be overdoing this shear, as the upper low is also forecast to fill and gradually dissipate by that time. And the trough appears to weak at 300-200 mb to produce appreciable shear over Danielle during this time.
Based on everything I've observed tonight, I have opted to go slightly higher than the NHC intensity scheme, and forecast an intensity of 105 mph (90 kt) at day five. However, there is still very much a chance that Danielle could strengthen further and become a major hurricane. The 18z GFDL reflects this possibility, forecasting a 101 knot hurricane at the end of the forecast period. This is certainly possible, given that vertical shear could decrease by late day four and into day five.
Interests in Bermuda, Atlantic Canada, and the East Coast of the United States should closely follow the progress of Danielle over the next several days.
Elsewhere
Elsewhere, some of the models are suggesting that the area of disturbed weather behind Danielle will develop into a tropical depression over the next few days. This is certainly possible, and will have to be watched closely over the coming days.
Tropical Storm Danielle has formed today in the eastern Atlantic Ocean several hundred miles west of the Cape Verde Islands. Here is the latest information from the National Hurricane Center, released at 5:00 PM EDT:
Maximum sustained winds: 50 mph, with higher gusts
Minimum central pressure: 1000 mb
Movement: NW at 13 mph
Location: 14.2°N 35.9°W
Shortwave infrared satellite images suggest that the circulation center is almost completely tucked underneath the large mass of very deep convection, but is very slightly exposed to the east. In fact, cloud tops are as cold as -90°C near the middle of the large convective ball.
There is still no evidence of upper-level outflow in the eastern semicircle, due to the continuance of strong easterly shear, analyzed as high as 30 knots by data from the University of Wisconsin's CIMSS. However, given current organizational trends on satellite imagery, I do not believe that the shear is as strong as is being analyzed by CIMSS. This shear is being induced in part by a large and complex area of disturbed weather several hundred miles to the east of Danielle, which some models forecast will become the season's next tropical depression over the next several days, and also partly by an intensifying upper-level anticyclone centered to the north of Danielle.
The cyclone currently appears to be moving NW, based on low cloud motions observed on satellite imagery. However, water vapor animations and 500 mb steering data from CIMSS suggest that this is merely a temporary motion, albeit pronounced, and Danielle should resume a WNW track over the next 6-12 hours. And based on water vapor imagery, a due W motion is even possible as Danielle nears 45W. But this will depend upon how the subtropical ridge evolves over the coming days. But this is a possibility that needs to be carefully assessed.
Based on water vapor animations and various other steering data, I strongly believe that the models are overdoing the trough and the consequent weakness in the Atlantic subtropical ridge. The culprit for potential recurvature that the models are seeing is a vigorous mid- to upper-level trough currently centered across the west-central United States. Though it cannot be said with absolute certainty at this juncture, it is quite possible that this trough will emerge too far north to completely recurve Danielle.
All of the models unanimously agree on Danielle moving generally WNW for the next 72 hours or so with a gradual increase in forward speed, after which point the subtropical ridge is forecast to reveal a weakness from 60 to 70W as the aforementioned trough emerges from the mid-Atlantic or New England. At that point, a gradual deceleration can be expected, and Danielle will likely turn NW after 72 hours, and could turn N by day four or five. However, this is becoming less likely. Instead, a slow NW motion should be expected by that time.
Beyond 120 hours, most of the models show a reestablishment of the subtropical ridge to the north of the system, which would tend to favor a more W track at the end of the forecast period. So for now, I agree with the NHC's current forecast track, given the strong uncertainty, greater than usual, in the forecast track.
The intensity forecast, thankfully, is much easier. The currently easterly shear should abate by tomorrow as the aforementioned anticyclone becomes more collocated with Danielle. It should then move in tandem with the cyclone for the next three days, providing a low shear environment favorable for strengthening. After 72 hours, southwesterly shear is forecast to increase as Danielle encounters an upper low currently centered in the central Atlantic Ocean. However, I feel the GFS may be overdoing this shear, as the upper low is also forecast to fill and gradually dissipate by that time. And the trough appears to weak at 300-200 mb to produce appreciable shear over Danielle during this time.
Based on everything I've observed tonight, I have opted to go slightly higher than the NHC intensity scheme, and forecast an intensity of 105 mph (90 kt) at day five. However, there is still very much a chance that Danielle could strengthen further and become a major hurricane. The 18z GFDL reflects this possibility, forecasting a 101 knot hurricane at the end of the forecast period. This is certainly possible, given that vertical shear could decrease by late day four and into day five.
Interests in Bermuda, Atlantic Canada, and the East Coast of the United States should closely follow the progress of Danielle over the next several days.
Elsewhere
Elsewhere, some of the models are suggesting that the area of disturbed weather behind Danielle will develop into a tropical depression over the next few days. This is certainly possible, and will have to be watched closely over the coming days.
Friday, August 20, 2010
Tropical weather analysis - August 20, 2010
Invest 95L
A broad area of low pressure, associated with a large area of disturbed weather within the ITCZ, is centered a couple hundred miles south-southwest of the Cape Verde Islands. This area was designated "Invest 95L" by the National Hurricane Center early this morning. Satellite animations suggest that the system is gradually becoming better organized, but shower activity is not persistent yet, and in fact, has waned markedly in recent hours. Additionally, vorticity data from CIMSS indicates that, although the low- and mid-level circulations are gradually becoming better organized, this system still has quite a bit of work to do, namely detaching itself from the active ITCZ in which it is currently embedded. The aforementioned vorticity data reveals that 95L is embedded within a large scale cyclonic circulation associated with an active ITCZ.
95L is currently moving W under the influence of a well-defined low- to mid-tropospheric ridge. This general motion should continue until a more WNW component becomes established in about two days. By about four days, the models are in unanimous agreement on a highly amplified mid- to upper-level pattern, as an unseasonably powerful trough erodes the subtropical ridge. At this point, 95L (by then a powerful hurricane) is forecast to approach this weakness and begin turning more poleward with a decrease in forward speed.
However, this is where the forecast gets tricky. Not all of the models agree on there being enough troughing to completely recurve the system, at least insofar as Bermuda is concerned. The CMC depicts the strongest trough, allowing 95L to completely recurve well east of Bermuda, and the GFDL and GFS follow suit, though depict a somewhat weaker trough. The HWRF, NOGAPS, and ECMWF depict a less amplified trough, and keep a more zonal flow in place, maintaining the Atlantic subtropical ridge enough to prevent complete recurvature prior to reaching the longitude of Bermuda. In fact, the 12z ECMWF is indicating that 95L will approach the southeast United States coast in approximately ten days, though this may be related more to the fact that it keeps the system quite weak until this time, and therefore it follows the low-level flow.
Regardless, there are still a number of possible scenarios for this system, though eventual recurvature seems probable, it's just the degree and timing of such that's uncertain at this juncture.
95L is currently experiencing about 15 kt of easterly shear. The 18z GFS keeps the shear quite weak throughout the forecast period, and even starts to develop an 200 mb anticyclone over the system in as little as 24 hours. The anticyclone becomes particularly well-established by 48 hours, and continues to strengthen throughout much of the forecast period. It should also move in tandem with 95L, particularly beyond 48 hours. These conditions should allow 95L to ultimately become the season's second hurricane, and quite possibly, the first major hurricane, as well.
In the short-term though, 95L has work to do. I feel the models are developing this a little too quickly, with some doing it as early as tomorrow. I will forecast continued slow development, and I expect this system to become a tropical depression on Monday afternoon. It should be noted that the weaker the system stays, the more westward it goes.
Residents along the Leeward Islands and Puerto Rico, as well as Bermuda and the east coast from North Carolina to Atlantic Canada should monitor the progress of this system very carefully over the coming days, given the inherent uncertainties ever present in long-range forecasts.
Elsewhere
There really isn't much going on in the tropics at the moment, other than Invest 95L. However, most of the models agree on a piece of 850 mb vorticity detaching from the aforementioned trough in about four days, the one forecast to recurve 95L. This trough split is forecast to occur along the warm waters of the Gulf Stream offshore the east coast of the United States, so this bears watching.
There are also a couple of decent looking entities over Africa, at around 8 to 11N, which may be identified as tropical waves later on as they emerge into the eastern Atlantic. These features have some rather decent cyclonic circulations, so they certainly bear watching as they move into the Atlantic over the next several days.
A broad area of low pressure, associated with a large area of disturbed weather within the ITCZ, is centered a couple hundred miles south-southwest of the Cape Verde Islands. This area was designated "Invest 95L" by the National Hurricane Center early this morning. Satellite animations suggest that the system is gradually becoming better organized, but shower activity is not persistent yet, and in fact, has waned markedly in recent hours. Additionally, vorticity data from CIMSS indicates that, although the low- and mid-level circulations are gradually becoming better organized, this system still has quite a bit of work to do, namely detaching itself from the active ITCZ in which it is currently embedded. The aforementioned vorticity data reveals that 95L is embedded within a large scale cyclonic circulation associated with an active ITCZ.
95L is currently moving W under the influence of a well-defined low- to mid-tropospheric ridge. This general motion should continue until a more WNW component becomes established in about two days. By about four days, the models are in unanimous agreement on a highly amplified mid- to upper-level pattern, as an unseasonably powerful trough erodes the subtropical ridge. At this point, 95L (by then a powerful hurricane) is forecast to approach this weakness and begin turning more poleward with a decrease in forward speed.
However, this is where the forecast gets tricky. Not all of the models agree on there being enough troughing to completely recurve the system, at least insofar as Bermuda is concerned. The CMC depicts the strongest trough, allowing 95L to completely recurve well east of Bermuda, and the GFDL and GFS follow suit, though depict a somewhat weaker trough. The HWRF, NOGAPS, and ECMWF depict a less amplified trough, and keep a more zonal flow in place, maintaining the Atlantic subtropical ridge enough to prevent complete recurvature prior to reaching the longitude of Bermuda. In fact, the 12z ECMWF is indicating that 95L will approach the southeast United States coast in approximately ten days, though this may be related more to the fact that it keeps the system quite weak until this time, and therefore it follows the low-level flow.
Regardless, there are still a number of possible scenarios for this system, though eventual recurvature seems probable, it's just the degree and timing of such that's uncertain at this juncture.
95L is currently experiencing about 15 kt of easterly shear. The 18z GFS keeps the shear quite weak throughout the forecast period, and even starts to develop an 200 mb anticyclone over the system in as little as 24 hours. The anticyclone becomes particularly well-established by 48 hours, and continues to strengthen throughout much of the forecast period. It should also move in tandem with 95L, particularly beyond 48 hours. These conditions should allow 95L to ultimately become the season's second hurricane, and quite possibly, the first major hurricane, as well.
In the short-term though, 95L has work to do. I feel the models are developing this a little too quickly, with some doing it as early as tomorrow. I will forecast continued slow development, and I expect this system to become a tropical depression on Monday afternoon. It should be noted that the weaker the system stays, the more westward it goes.
Residents along the Leeward Islands and Puerto Rico, as well as Bermuda and the east coast from North Carolina to Atlantic Canada should monitor the progress of this system very carefully over the coming days, given the inherent uncertainties ever present in long-range forecasts.
Elsewhere
There really isn't much going on in the tropics at the moment, other than Invest 95L. However, most of the models agree on a piece of 850 mb vorticity detaching from the aforementioned trough in about four days, the one forecast to recurve 95L. This trough split is forecast to occur along the warm waters of the Gulf Stream offshore the east coast of the United States, so this bears watching.
There are also a couple of decent looking entities over Africa, at around 8 to 11N, which may be identified as tropical waves later on as they emerge into the eastern Atlantic. These features have some rather decent cyclonic circulations, so they certainly bear watching as they move into the Atlantic over the next several days.
Tuesday, August 10, 2010
Tropical weather analysis - August 10, 2010
Tropical Depression Five
Invest 94L developed into Tropical Depression Five this afternoon in the eastern Gulf of Mexico. As of the 7:30 PM EDT advisory from the National Hurricane Center, the center was estimated to be near 26.0°N 84.1°W, moving NW at 6 mph. The minimum central pressure is estimated at 1007 mb. Visible satellite animations suggest that though the overall circulation is quite vigorous, large, and well-defined, the cyclone lacks deep convection near the assumed center.
The environment across the Gulf of Mexico is characterized by light easterly shear and some minor subsidence (dry air), as noted on water vapor imagery. Water vapor imagery also depicts a weak upper low centered about 100 miles to the north of the depression. This low appears to be moving rapidly toward the west, however, and this feature is forecast by the 18z GFS to quickly lift out and deamplify while moving westward toward the upper Texas coast. This upper low is currently having a slight negative effect on TD5, with a small dry slot seen to the northwest of the center on water vapor imagery. As the low lifts out, however, the environment will become more favorable, characterized by less subsidence and more uplift. This should allow the cyclone to begin intensifying at a more steady rate in around 12 hours.
Further supporting the GFS' forecast of a rapidly weakening and deamplifying upper low is 200 mb vorticity data from CIMSS, which strongly implies that said upper low has significantly weakened over the last six hours, while having moved westward. There are also indications within the mid- upper level steering that the upper low will move away from the depression at a very rapid rate. I am expecting a general W motion of the upper low throughout the next two days until it reaches the upper Texas coast and dissipates, although a slightly S of due W component of motion cannot be ruled out in the near-term.
Regardless, it appears that the upper low will have a negative influence of TD5 for about the next 12 hours. My own forecast track is in best agreement with the 12z UKMET, which moves the system WNW within the next 6-12 hours, followed by a steady WNW motion until landfall. My track takes the system inland near Cocodrie in two days. I feel the UKMET is a little slow in bringing this system inland, however (60 hours). Based on the current and forecast steering, I would expect to see a bit of a westward shift of the NHC's track over the next day or so, along with the models. At this time, a landfall between Intracoastal City and Buras cannot be ruled out, but the greatest threat appears to be central Louisiana at this time.
Nevertheless, given the uncertainty, residents from Intracoastal City, Louisiana eastward to Pensacola, Florida should closely monitor the progress of the depression over the next couple of days. Should the depression take a day or so longer to move ashore, as predicted by some models, it would likely become stronger than is currently being forecast by the NHC or myself.
All in all, the NHC's current track looks good, but I'm just a bit to the west of that. Some moderate easterly should could develop over the system in about 24-30 as hours as the high pressure ridge to the north strengthens. However, given that the cyclone will be moving roughly in tandem with the upper flow, I am not expecting this to slow intensification significantly. In fact, I think the current NHC forecast of only 45 mph is much too low. I'm going with 60 mph at the moment.
Watches and warnings
A tropical storm warning has been issued from:
Destin, Florida to Intracoastal City, Louisiana. This includes the city of New Orleans and Lake Pontchartrain.
Invest 94L developed into Tropical Depression Five this afternoon in the eastern Gulf of Mexico. As of the 7:30 PM EDT advisory from the National Hurricane Center, the center was estimated to be near 26.0°N 84.1°W, moving NW at 6 mph. The minimum central pressure is estimated at 1007 mb. Visible satellite animations suggest that though the overall circulation is quite vigorous, large, and well-defined, the cyclone lacks deep convection near the assumed center.
The environment across the Gulf of Mexico is characterized by light easterly shear and some minor subsidence (dry air), as noted on water vapor imagery. Water vapor imagery also depicts a weak upper low centered about 100 miles to the north of the depression. This low appears to be moving rapidly toward the west, however, and this feature is forecast by the 18z GFS to quickly lift out and deamplify while moving westward toward the upper Texas coast. This upper low is currently having a slight negative effect on TD5, with a small dry slot seen to the northwest of the center on water vapor imagery. As the low lifts out, however, the environment will become more favorable, characterized by less subsidence and more uplift. This should allow the cyclone to begin intensifying at a more steady rate in around 12 hours.
Further supporting the GFS' forecast of a rapidly weakening and deamplifying upper low is 200 mb vorticity data from CIMSS, which strongly implies that said upper low has significantly weakened over the last six hours, while having moved westward. There are also indications within the mid- upper level steering that the upper low will move away from the depression at a very rapid rate. I am expecting a general W motion of the upper low throughout the next two days until it reaches the upper Texas coast and dissipates, although a slightly S of due W component of motion cannot be ruled out in the near-term.
Regardless, it appears that the upper low will have a negative influence of TD5 for about the next 12 hours. My own forecast track is in best agreement with the 12z UKMET, which moves the system WNW within the next 6-12 hours, followed by a steady WNW motion until landfall. My track takes the system inland near Cocodrie in two days. I feel the UKMET is a little slow in bringing this system inland, however (60 hours). Based on the current and forecast steering, I would expect to see a bit of a westward shift of the NHC's track over the next day or so, along with the models. At this time, a landfall between Intracoastal City and Buras cannot be ruled out, but the greatest threat appears to be central Louisiana at this time.
Nevertheless, given the uncertainty, residents from Intracoastal City, Louisiana eastward to Pensacola, Florida should closely monitor the progress of the depression over the next couple of days. Should the depression take a day or so longer to move ashore, as predicted by some models, it would likely become stronger than is currently being forecast by the NHC or myself.
All in all, the NHC's current track looks good, but I'm just a bit to the west of that. Some moderate easterly should could develop over the system in about 24-30 as hours as the high pressure ridge to the north strengthens. However, given that the cyclone will be moving roughly in tandem with the upper flow, I am not expecting this to slow intensification significantly. In fact, I think the current NHC forecast of only 45 mph is much too low. I'm going with 60 mph at the moment.
Watches and warnings
A tropical storm warning has been issued from:
Destin, Florida to Intracoastal City, Louisiana. This includes the city of New Orleans and Lake Pontchartrain.
Monday, August 9, 2010
Tropical weather analysis - August 9, 2010
Invest 93L
Invest 93L continues to churn out in the central Atlantic Ocean, about 875 miles east-northeast of the Leeward Islands. Latest shortwave infrared imagery reveals that this system is still disorganized, with the well-defined surface circulation clearly evident at 23N 50W, moving WNW at 10 to 15 mph. This center is completely exposed from the pulsating deep convection, as has been the case over the last couple days. However, it looks even less organized today than 24 hours ago, with any deep convection displaced over 100 miles to the east and northeast of the system.
Additionally, CIMSS vorticity data suggests a vertical decoupling of the 850 and 500 mb circulations. CIMSS vertical shear analysis indicates only 5 kt of southwesterly shear over the center of the system, with 20 kt on the western side. Certainly, satellite-observed low-cloud motions seem to indicate a relaxation of the shear, confirming the analysis from CIMSS.
93L is being steered by a low- to mid-level tropospheric ridge to the north. A weakness is evident in the ridge near 60W westward to nearly 75W. The models suggest that this general motion should continue until around 24 hour, at which point a turn to the NW with some deceleration is expected as 93L rounds the aforementioned weakness in the Atlantic subtropical ridge. By 36 hours or so, a turn to the N should occur, followed by a turn to the NE by 48-54 hours. This is a rather fortunate track scenario, taking the system completely out to sea. The models differ drastically as to how strong 93L will get, and when.
The GFDL and HWRF models take the system to hurricane status on day four as the system interacts more strongly with the trough. We have seen trough interactions fuel intensification in the past, so this possibility cannot be ruled out. And given that sea surface temperatures (SSTs) in this area, 35 to 40N 45 to 50W, where the aforementioned models foresee hurricane status, are running at 26 to 28C, this is probably not baroclinic strengthening being foreseen in these models.
The remainder of the models are less bullish, and peak the system about a day earlier. I will compromise between these extremes, and still, for the third consecutive day, forecast this system to peak at 65 mph in about 84 hours. I tend to lean toward the latter camp (GFS, ECMWF, UKMET, CMC, and NOGAPS) more strongly, based on previous and current convective trends, along with shear forecasts from the GFS. Nevertheless, environmental conditions are slowly becoming more favorable for development, with a lowering of the shear today (with further lowering expected), along with a gradual dissipation of the dry air, as noted on water vapor imagery.
I still expect this system to eventually become a tropical cyclone.
Invest 94L
The basin's biggest threat is still Invest 94L, a broad area of low pressure located in the extreme eastern Gulf of Mexico off the southwestern coast of Florida. My best estimate of the broad surface center, based on the remaining visible satellite images, doppler radar animations, and CIMSS 850 mb vorticity data is 25N 81W. Recent convective trends suggest that 94L is attempting to organize, with the development of a small area of deep convection over its estimated center.
Some modest pressure falls have been noted across the area this afternoon, and buoy observations across the eastern Gulf suggest that the system maintains its closed surface circulation, and that it might have become even better defined today.
The key player in the genesis, or lack thereof, of Invest 94L will be a newly-developed upper low just to the north of the northern Bahamas. Currently, this low is moving west-northwest, while 94L is moving west-southwest. Steering data from CIMSS suggests a WSW motion should continue for the next 6-12 hours, after which point a turn to the WNW should occur, followed by a turn to the NW in about 72 hours as the system nears the northern Gulf Coast. The majority of the models still bring this system into southeast or eastern Louisiana in about 72 hours, and the 18z GFDL makes this system a hurricane and brings it west of New Orleans. I will not go that high just yet, because I want to see the evolution of the aforementioned upper low first, as if it gets close enough, it could shear 94L, and inhibit significant development.
The 18z GFS suggests that the upper low will move generally westward and gradually weaken and deamplify as it does so. Additionally, steering data from PSU's e-wall suggests that the upper low could well outrun Invest 94L, leaving behind a very favorable upper environment as upper ridging builds overhead. In addition, the shear is forecast to be very light, and the currently northerly shear is forecast to abate soon, and veer to easterly or southeasterly by 24 hours. The shear may switch back around to northeasterly and become stronger again before the system moves inland.
There are three possibilities right now with 94L:
1. It ultimately becomes sheared and dissipated due to the upper low.
2. It becomes a tropical cyclone.
3. It becomes a subtropical cyclone.
Based on what I've seen, I'm expecting tropical cyclogenesis to occur with this wave by tomorrow night or Wednesday morning. However, this will be highly dependent upon the evolution and strength of the upper low. Subtropical development could also occur if the two become vertically aligned, or near so. A reconnaissance aircraft is scheduled to investigate this system tomorrow, if necessary.
Residents along the northern Gulf Coast from Biloxi to Morgan City should closely follow the evolution of this system over the next several days. Regardless of development, locally heavy rainfall, above normal tides, and strong gusty winds will overspread portions of the aforementioned areas during the next few days.
Invest 93L continues to churn out in the central Atlantic Ocean, about 875 miles east-northeast of the Leeward Islands. Latest shortwave infrared imagery reveals that this system is still disorganized, with the well-defined surface circulation clearly evident at 23N 50W, moving WNW at 10 to 15 mph. This center is completely exposed from the pulsating deep convection, as has been the case over the last couple days. However, it looks even less organized today than 24 hours ago, with any deep convection displaced over 100 miles to the east and northeast of the system.
Additionally, CIMSS vorticity data suggests a vertical decoupling of the 850 and 500 mb circulations. CIMSS vertical shear analysis indicates only 5 kt of southwesterly shear over the center of the system, with 20 kt on the western side. Certainly, satellite-observed low-cloud motions seem to indicate a relaxation of the shear, confirming the analysis from CIMSS.
93L is being steered by a low- to mid-level tropospheric ridge to the north. A weakness is evident in the ridge near 60W westward to nearly 75W. The models suggest that this general motion should continue until around 24 hour, at which point a turn to the NW with some deceleration is expected as 93L rounds the aforementioned weakness in the Atlantic subtropical ridge. By 36 hours or so, a turn to the N should occur, followed by a turn to the NE by 48-54 hours. This is a rather fortunate track scenario, taking the system completely out to sea. The models differ drastically as to how strong 93L will get, and when.
The GFDL and HWRF models take the system to hurricane status on day four as the system interacts more strongly with the trough. We have seen trough interactions fuel intensification in the past, so this possibility cannot be ruled out. And given that sea surface temperatures (SSTs) in this area, 35 to 40N 45 to 50W, where the aforementioned models foresee hurricane status, are running at 26 to 28C, this is probably not baroclinic strengthening being foreseen in these models.
The remainder of the models are less bullish, and peak the system about a day earlier. I will compromise between these extremes, and still, for the third consecutive day, forecast this system to peak at 65 mph in about 84 hours. I tend to lean toward the latter camp (GFS, ECMWF, UKMET, CMC, and NOGAPS) more strongly, based on previous and current convective trends, along with shear forecasts from the GFS. Nevertheless, environmental conditions are slowly becoming more favorable for development, with a lowering of the shear today (with further lowering expected), along with a gradual dissipation of the dry air, as noted on water vapor imagery.
I still expect this system to eventually become a tropical cyclone.
Invest 94L
The basin's biggest threat is still Invest 94L, a broad area of low pressure located in the extreme eastern Gulf of Mexico off the southwestern coast of Florida. My best estimate of the broad surface center, based on the remaining visible satellite images, doppler radar animations, and CIMSS 850 mb vorticity data is 25N 81W. Recent convective trends suggest that 94L is attempting to organize, with the development of a small area of deep convection over its estimated center.
Some modest pressure falls have been noted across the area this afternoon, and buoy observations across the eastern Gulf suggest that the system maintains its closed surface circulation, and that it might have become even better defined today.
The key player in the genesis, or lack thereof, of Invest 94L will be a newly-developed upper low just to the north of the northern Bahamas. Currently, this low is moving west-northwest, while 94L is moving west-southwest. Steering data from CIMSS suggests a WSW motion should continue for the next 6-12 hours, after which point a turn to the WNW should occur, followed by a turn to the NW in about 72 hours as the system nears the northern Gulf Coast. The majority of the models still bring this system into southeast or eastern Louisiana in about 72 hours, and the 18z GFDL makes this system a hurricane and brings it west of New Orleans. I will not go that high just yet, because I want to see the evolution of the aforementioned upper low first, as if it gets close enough, it could shear 94L, and inhibit significant development.
The 18z GFS suggests that the upper low will move generally westward and gradually weaken and deamplify as it does so. Additionally, steering data from PSU's e-wall suggests that the upper low could well outrun Invest 94L, leaving behind a very favorable upper environment as upper ridging builds overhead. In addition, the shear is forecast to be very light, and the currently northerly shear is forecast to abate soon, and veer to easterly or southeasterly by 24 hours. The shear may switch back around to northeasterly and become stronger again before the system moves inland.
There are three possibilities right now with 94L:
1. It ultimately becomes sheared and dissipated due to the upper low.
2. It becomes a tropical cyclone.
3. It becomes a subtropical cyclone.
Based on what I've seen, I'm expecting tropical cyclogenesis to occur with this wave by tomorrow night or Wednesday morning. However, this will be highly dependent upon the evolution and strength of the upper low. Subtropical development could also occur if the two become vertically aligned, or near so. A reconnaissance aircraft is scheduled to investigate this system tomorrow, if necessary.
Residents along the northern Gulf Coast from Biloxi to Morgan City should closely follow the evolution of this system over the next several days. Regardless of development, locally heavy rainfall, above normal tides, and strong gusty winds will overspread portions of the aforementioned areas during the next few days.
Sunday, August 8, 2010
Tropical weather analysis - August 8, 2010
Colin
Tropical Depression Colin degenerated into an open trough of low pressure earlier this afternoon. Regeneration is not expected as the system moves NNE to NE within the southwesterly flow associated with a deep-layer trough exiting the east coast of the United States. Colin, or rather, what's left of it, will ultimately make extratropical transition and subsequently become absorbed into said trough over the next several days. Some rain showers and gusty winds are still possible across Bermuda, but nothing significant. However, some isolated tropical storm force wind gusts, specifically along higher elevations, have been reported on the island.
Invest 93L
Invest 93L, located several hundred miles west-northwest of the Cape Verde Islands, continues to display signs of organization. Shortwave infrared satellite animations suggest that the center is located at 23N 46W, moving WNW. Earlier this afternoon, visible satellite animations clearly depicted a closed surface circulation, albeit exposed from the deep convection due to strong vertical shear. This is still the case this evening, with the well-defined surface center (which is closed) displaced well to the southwest of the pulsating deep convection. 93L continues to be embedded within a relatively dry environment, evidenced on water vapor loops. This, in conjunction with the aforementioned vertical shear, analyzed at 10-20 kt by data from the University of Wisconsin CIMSS, should preclude any rapid development over the next day or so.
This system has been slow to develop, which wasn't really unexpected given the meager environment in which it is currently embedded. But I must admit, this system has certainly developed slower than I thought it would. I thought for sure that by tonight or early tomorrow morning, it would have been labeled a tropical depression.
Additionally, CIMSS vorticity data suggests a vertical decoupling of the low- and mid-level circulations. This is undoubtedly due to the aforementioned shear, which is being induced by an upper-level low several hundred miles west of Invest 93L. All of these negative factors notwithstanding, however, vertical shear has decreased over the system during the last 12 hours. Vertical shear is forecast to ease somewhat over the next several days as the upper low deamplifies and retreats slightly northward. In fact, the 18z GFS suggests that the system will move in tandem with a weak upper-level anticyclone currently centered just to the south of the disturbance. The GFS foresees 93L losing the anticyclone after about 60 or 66 hours. Though shear will increase over the system subsequent to this, it will still be weak enough to allow slow intensification, because the system will probably be moving in tandem with the upper flow beginning in about 84-90 hours.
I expect a continued WNW motion, followed by a gentle bend to the NW with a deceleration in the forward speed beginning in about 48-54 hours as the subtropical ridge weakens with the approach of the powerful longwave trough that recurved Colin. Thereafter, a gradual turn to the N is expected late on day two, followed by a swing to the NE with a gradual increase in forward speed expected late on day three or very early day four.
None of the models significantly intensify the system, and most barely depict it as a perturbation. Though I will still forecast gradual intensification, peaking the system at 65 mph, the models could certainly be onto something given how hesitant this system has been to develop since its designation as an invest. I will continue to carefully assess this possibility.
Invest 94L
An area of disturbed weather located just offshore the Florida east coast was designated "Invest 94L" this afternoon by the National Hurricane Center. The poorly defined center is estimated to be about 75 miles east of Vero Beach, moving slowly to the SW. Surface, buoy, and ASCAT observations suggest that a broad but closed circulation may exist at the surface. Surface pressures are somewhat low in the area, but not overly so, and are not significantly falling at this time.
94L is currently experiencing 20 kt of northwesterly shear induced by the longwave trough currently recurving Colin. This has resulted in a vertical decoupling of the low and mid-level circulation centers, with the latter being displaced about 35-50 miles southeast of the low-level center. In addition to the shear, dry air is being entrained into the circulation due to the aforementioned northwesterly shear. These factors should inhibit any significant development over the next day or two.
Current steering/model data suggests that 94L will be slow to move inland, and most of the models do not bring it inland over central or eastern Florida until around 36 hours. This is certainly possible, and this will be a difficult storm to forecast in the near-term due to the weak steering regime in the region. It is entirely possible that this system could perform an anticyclonic loop over the next day or so. However, I will instead forecast a general, but quite slow (5 mph or less at times) motion to the SW, in agreement with the models and the overall synoptic scale steering pattern.
Thereafter, the system is forecast to pick up speed and emerge into the Gulf of Mexico. This is where the forecast begins to get easier. Most of the models take this system inland over eastern or southeastern Louisiana sometime on Thursday, though many of them do not show much of a surface reflection. This is likely due to the fact that it doesn't appear to have more than a couple days over water after emerging into the Gulf.
After 36 hours, the upper-level winds will relax significantly as upper ridging replaces the current upper troughing. Furthermore, because 94L will be moving WNW, in tandem with the forecast upper-level winds at day two and beyond, it is a good possibility that this system will try and undergo tropical cyclogenesis while moving across the eastern and northern Gulf of Mexico.
I give this system a 40% chance of eventually becoming a tropical cyclone, and residents from Destin to Beaumont should carefully monitor the progress of this system over the next several days. Though at this time, based on the models, it appears that southeast Louisiana is the most likely target for an eventual landfall.
Regardless of development, heavy rainfall will continue spreading over portions of central and south Florida over the next day or two, potentially causing some localized flooding.
Tropical Depression Colin degenerated into an open trough of low pressure earlier this afternoon. Regeneration is not expected as the system moves NNE to NE within the southwesterly flow associated with a deep-layer trough exiting the east coast of the United States. Colin, or rather, what's left of it, will ultimately make extratropical transition and subsequently become absorbed into said trough over the next several days. Some rain showers and gusty winds are still possible across Bermuda, but nothing significant. However, some isolated tropical storm force wind gusts, specifically along higher elevations, have been reported on the island.
Invest 93L
Invest 93L, located several hundred miles west-northwest of the Cape Verde Islands, continues to display signs of organization. Shortwave infrared satellite animations suggest that the center is located at 23N 46W, moving WNW. Earlier this afternoon, visible satellite animations clearly depicted a closed surface circulation, albeit exposed from the deep convection due to strong vertical shear. This is still the case this evening, with the well-defined surface center (which is closed) displaced well to the southwest of the pulsating deep convection. 93L continues to be embedded within a relatively dry environment, evidenced on water vapor loops. This, in conjunction with the aforementioned vertical shear, analyzed at 10-20 kt by data from the University of Wisconsin CIMSS, should preclude any rapid development over the next day or so.
This system has been slow to develop, which wasn't really unexpected given the meager environment in which it is currently embedded. But I must admit, this system has certainly developed slower than I thought it would. I thought for sure that by tonight or early tomorrow morning, it would have been labeled a tropical depression.
Additionally, CIMSS vorticity data suggests a vertical decoupling of the low- and mid-level circulations. This is undoubtedly due to the aforementioned shear, which is being induced by an upper-level low several hundred miles west of Invest 93L. All of these negative factors notwithstanding, however, vertical shear has decreased over the system during the last 12 hours. Vertical shear is forecast to ease somewhat over the next several days as the upper low deamplifies and retreats slightly northward. In fact, the 18z GFS suggests that the system will move in tandem with a weak upper-level anticyclone currently centered just to the south of the disturbance. The GFS foresees 93L losing the anticyclone after about 60 or 66 hours. Though shear will increase over the system subsequent to this, it will still be weak enough to allow slow intensification, because the system will probably be moving in tandem with the upper flow beginning in about 84-90 hours.
I expect a continued WNW motion, followed by a gentle bend to the NW with a deceleration in the forward speed beginning in about 48-54 hours as the subtropical ridge weakens with the approach of the powerful longwave trough that recurved Colin. Thereafter, a gradual turn to the N is expected late on day two, followed by a swing to the NE with a gradual increase in forward speed expected late on day three or very early day four.
None of the models significantly intensify the system, and most barely depict it as a perturbation. Though I will still forecast gradual intensification, peaking the system at 65 mph, the models could certainly be onto something given how hesitant this system has been to develop since its designation as an invest. I will continue to carefully assess this possibility.
Invest 94L
An area of disturbed weather located just offshore the Florida east coast was designated "Invest 94L" this afternoon by the National Hurricane Center. The poorly defined center is estimated to be about 75 miles east of Vero Beach, moving slowly to the SW. Surface, buoy, and ASCAT observations suggest that a broad but closed circulation may exist at the surface. Surface pressures are somewhat low in the area, but not overly so, and are not significantly falling at this time.
94L is currently experiencing 20 kt of northwesterly shear induced by the longwave trough currently recurving Colin. This has resulted in a vertical decoupling of the low and mid-level circulation centers, with the latter being displaced about 35-50 miles southeast of the low-level center. In addition to the shear, dry air is being entrained into the circulation due to the aforementioned northwesterly shear. These factors should inhibit any significant development over the next day or two.
Current steering/model data suggests that 94L will be slow to move inland, and most of the models do not bring it inland over central or eastern Florida until around 36 hours. This is certainly possible, and this will be a difficult storm to forecast in the near-term due to the weak steering regime in the region. It is entirely possible that this system could perform an anticyclonic loop over the next day or so. However, I will instead forecast a general, but quite slow (5 mph or less at times) motion to the SW, in agreement with the models and the overall synoptic scale steering pattern.
Thereafter, the system is forecast to pick up speed and emerge into the Gulf of Mexico. This is where the forecast begins to get easier. Most of the models take this system inland over eastern or southeastern Louisiana sometime on Thursday, though many of them do not show much of a surface reflection. This is likely due to the fact that it doesn't appear to have more than a couple days over water after emerging into the Gulf.
After 36 hours, the upper-level winds will relax significantly as upper ridging replaces the current upper troughing. Furthermore, because 94L will be moving WNW, in tandem with the forecast upper-level winds at day two and beyond, it is a good possibility that this system will try and undergo tropical cyclogenesis while moving across the eastern and northern Gulf of Mexico.
I give this system a 40% chance of eventually becoming a tropical cyclone, and residents from Destin to Beaumont should carefully monitor the progress of this system over the next several days. Though at this time, based on the models, it appears that southeast Louisiana is the most likely target for an eventual landfall.
Regardless of development, heavy rainfall will continue spreading over portions of central and south Florida over the next day or two, potentially causing some localized flooding.
Saturday, August 7, 2010
Tropical weather analysis - August 7, 2010
Tropical Storm Colin
Tropical Storm Colin continues to struggle to intensify. Visible satellite animations reveal quite nicely the partially exposed surface center along the western end of the deep convection. As of the 5:00 PM AST NHC advisory, maximum sustained winds are 40 mph, the minimum central pressure at 1012 mb, and the movement toward the NNE at 7 mph. Though the overall environment is undeniably more moisture-laden than it has been over the last couple days, there is still dry air evident to the west of the system, slowly being entrained (albeit to a lesser extent) into the western semicircle of the circulation thanks to a persistent but gradually weakening upper-level low a couple hundred miles to the southwest of Colin. Deep convection is shapeless and not very impressive or organized, according to infrared satellite animations.
Both CIMSS and satellite-derived data (low cloud motions) suggest that, though Colin is still disorganized, the vertical shear it has been battling over the last two days has significantly abated, with an expansion of convection finally occurring along the western portion of the circulation. Colin is well-embedded within a large weakness in the Atlantic subtropical ridge. The models suggest a generally N motion for the next 36-42 hours, followed by a NE motion. All in all, I agree with the NHC's current forecast track, and residents across Bermuda should continue monitoring the progress of the tropical cyclone over the next 24 hours or so, until it safely passes the island. Heavy rain squalls should begin affecting the island tonight and into the early morning hours on Sunday.
Watches and warnings
A tropical storm warning is in effect for:
Bermuda
A tropical storm warning means that tropical storm force winds are expected in the warning area within the next 36 hours.
All in all, I would expect 2 to 4 inches of rain to fall across the island, along with tropical storm force winds. Wind gusts could reach or exceed 50 mph. Upper-level winds appear favorable for Colin to intensify until about 48 hours, when upper-level winds will become unfavorable. Additionally, the cyclone will be passing over sub-26C SSTs by about this time. Extratropical transition should be complete by 60-66 hours. None of the models, save the GFDL and HWRF, make Colin a hurricane. These two models may be seeing some baroclinic intensification, since they bring it to hurricane status late on day two or early day three, when Colin is expected to be extratropical.
Residents living along Atlantic Canada should also follow the progress of Colin over the next couple of days, though I am not expecting a landfall here. I am also not expecting Colin to become a hurricane, even as an extratropical cyclone.
Invest 92L
A weak tropical wave moving across Belize (dubbed " Invest 92L" by the National Hurricane Center) remains highly disorganized, and is not a threat to develop into a tropical depression today. By tomorrow, however, it will have emerged into the Bay of Campeche, where it will need to be monitored for potential development. Upper-level winds appear to be only marginally conducive for development in the Bay of Campeche. I am not expecting any significant development of this system prior to it moving inland across northeast Mexico or extreme south Texas in about 48 hours.
Invest 93L
Another, more well-defined tropical wave, is located in the far eastern Atlantic Ocean about 1200 miles west-northwest of the Cape Verde Islands. This wave was designated "Invest 93L" by the National Hurricane Center on Thursday. Based on the last of the visible satellite images, my best estimate for the center position is 20N 40W. Because this wave is already at a rather high latitude for an easterly wave, eventual recurvature out to sea is a probable, nearly certain scenario. Though the overall low- and mid-level circulation is fairly well-defined, deep convection associated with this system is currently minimal, and confined to the north of the wave axis.
In addition, water vapor imagery depicts mid-level dry air around the system. This is the main inhibiting factor against development, though moderate southwesterly shear of 10-20 kt may also act to slow any immediate additional development of the system. Upper-level winds appear favorable for additional slow development of this disturbance as it moves WNW at around 15 to 20 mph over the next several days. By day four, vertical shear could increase a bit over the system, as it loses the upper-level anticyclone the GFS keeps over it for the first few days. The biggest inhibiting factor, as previously mentioned, will be dry air over the central Atlantic. Though this air is not nearly as dry as we've previously seen this season, it is certainly dry enough to inhibit any rapid development, even if upper-level shear is generally favorable.
Given all of these parameters, I expect 93L to continue to slowly develop, possibly organizing into a tropical depression tomorrow night or Monday morning. This system does not presently appear to be a pose a threat to any land areas, with the possible exception of Bermuda, and even that's iffy. By day four, another upper-level trough, albeit weaker than the last, will be approaching from the west, once again eroding the western Atlantic subtropical ridge, which will allow for a slowing of the forward speed by 72 hours, a turn to the NW by 96 hours, and a gradual bend to the N and NE thereafter.
It is possible that this system could become a hurricane, though if it wants to do so, it has a bit of work ahead of it. I'll peak the system as a 65 mph tropical storm.
Cape Verde Islands tropical wave
Another tropical wave, located southwest of the southern Cape Verde Islands, is also a threat to develop. This system could actually pose an eventual threat to land areas, so we need to carefully monitor the progress of this system over the next several days. Upper-level winds greatly favor development of this system, with a uniform 200 mb easterly flow foreseen by the GFS. None of the models are presently developing this system, but perhaps this is because the wave was not initialized all that well, if at all, within these models. As the wave's surface signature increases, the models may latch onto development. We'll have to see. This system has a better shot at ultimately becoming a hurricane than 93L does.
Gulf of Mexico disturbance
Most of the models have been predicting that a cutoff low will branch off in the northeastern Gulf of Mexico from the longwave trough recurving Colin in about 72 hours. The upper wind environment appears favorable for anything that might try and develop here. The eventual track of such a system is uncertain, but a landfall from Destin to New Orleans is probable at this juncture. Residents in these areas should closely monitor the progress of this potential system over the next several days.
Regardless of development, it appears that some locally heavy rainfall will be occurring over portions of the northeastern and northern Gulf Coast beginning in about 72 hours.
The models are not currently indicating much of a surface reflection with this feature, though they do depict it fairly well in the low- to mid-levels of the atmosphere.
Tropical Storm Colin continues to struggle to intensify. Visible satellite animations reveal quite nicely the partially exposed surface center along the western end of the deep convection. As of the 5:00 PM AST NHC advisory, maximum sustained winds are 40 mph, the minimum central pressure at 1012 mb, and the movement toward the NNE at 7 mph. Though the overall environment is undeniably more moisture-laden than it has been over the last couple days, there is still dry air evident to the west of the system, slowly being entrained (albeit to a lesser extent) into the western semicircle of the circulation thanks to a persistent but gradually weakening upper-level low a couple hundred miles to the southwest of Colin. Deep convection is shapeless and not very impressive or organized, according to infrared satellite animations.
Both CIMSS and satellite-derived data (low cloud motions) suggest that, though Colin is still disorganized, the vertical shear it has been battling over the last two days has significantly abated, with an expansion of convection finally occurring along the western portion of the circulation. Colin is well-embedded within a large weakness in the Atlantic subtropical ridge. The models suggest a generally N motion for the next 36-42 hours, followed by a NE motion. All in all, I agree with the NHC's current forecast track, and residents across Bermuda should continue monitoring the progress of the tropical cyclone over the next 24 hours or so, until it safely passes the island. Heavy rain squalls should begin affecting the island tonight and into the early morning hours on Sunday.
Watches and warnings
A tropical storm warning is in effect for:
Bermuda
A tropical storm warning means that tropical storm force winds are expected in the warning area within the next 36 hours.
All in all, I would expect 2 to 4 inches of rain to fall across the island, along with tropical storm force winds. Wind gusts could reach or exceed 50 mph. Upper-level winds appear favorable for Colin to intensify until about 48 hours, when upper-level winds will become unfavorable. Additionally, the cyclone will be passing over sub-26C SSTs by about this time. Extratropical transition should be complete by 60-66 hours. None of the models, save the GFDL and HWRF, make Colin a hurricane. These two models may be seeing some baroclinic intensification, since they bring it to hurricane status late on day two or early day three, when Colin is expected to be extratropical.
Residents living along Atlantic Canada should also follow the progress of Colin over the next couple of days, though I am not expecting a landfall here. I am also not expecting Colin to become a hurricane, even as an extratropical cyclone.
Invest 92L
A weak tropical wave moving across Belize (dubbed " Invest 92L" by the National Hurricane Center) remains highly disorganized, and is not a threat to develop into a tropical depression today. By tomorrow, however, it will have emerged into the Bay of Campeche, where it will need to be monitored for potential development. Upper-level winds appear to be only marginally conducive for development in the Bay of Campeche. I am not expecting any significant development of this system prior to it moving inland across northeast Mexico or extreme south Texas in about 48 hours.
Invest 93L
Another, more well-defined tropical wave, is located in the far eastern Atlantic Ocean about 1200 miles west-northwest of the Cape Verde Islands. This wave was designated "Invest 93L" by the National Hurricane Center on Thursday. Based on the last of the visible satellite images, my best estimate for the center position is 20N 40W. Because this wave is already at a rather high latitude for an easterly wave, eventual recurvature out to sea is a probable, nearly certain scenario. Though the overall low- and mid-level circulation is fairly well-defined, deep convection associated with this system is currently minimal, and confined to the north of the wave axis.
In addition, water vapor imagery depicts mid-level dry air around the system. This is the main inhibiting factor against development, though moderate southwesterly shear of 10-20 kt may also act to slow any immediate additional development of the system. Upper-level winds appear favorable for additional slow development of this disturbance as it moves WNW at around 15 to 20 mph over the next several days. By day four, vertical shear could increase a bit over the system, as it loses the upper-level anticyclone the GFS keeps over it for the first few days. The biggest inhibiting factor, as previously mentioned, will be dry air over the central Atlantic. Though this air is not nearly as dry as we've previously seen this season, it is certainly dry enough to inhibit any rapid development, even if upper-level shear is generally favorable.
Given all of these parameters, I expect 93L to continue to slowly develop, possibly organizing into a tropical depression tomorrow night or Monday morning. This system does not presently appear to be a pose a threat to any land areas, with the possible exception of Bermuda, and even that's iffy. By day four, another upper-level trough, albeit weaker than the last, will be approaching from the west, once again eroding the western Atlantic subtropical ridge, which will allow for a slowing of the forward speed by 72 hours, a turn to the NW by 96 hours, and a gradual bend to the N and NE thereafter.
It is possible that this system could become a hurricane, though if it wants to do so, it has a bit of work ahead of it. I'll peak the system as a 65 mph tropical storm.
Cape Verde Islands tropical wave
Another tropical wave, located southwest of the southern Cape Verde Islands, is also a threat to develop. This system could actually pose an eventual threat to land areas, so we need to carefully monitor the progress of this system over the next several days. Upper-level winds greatly favor development of this system, with a uniform 200 mb easterly flow foreseen by the GFS. None of the models are presently developing this system, but perhaps this is because the wave was not initialized all that well, if at all, within these models. As the wave's surface signature increases, the models may latch onto development. We'll have to see. This system has a better shot at ultimately becoming a hurricane than 93L does.
Gulf of Mexico disturbance
Most of the models have been predicting that a cutoff low will branch off in the northeastern Gulf of Mexico from the longwave trough recurving Colin in about 72 hours. The upper wind environment appears favorable for anything that might try and develop here. The eventual track of such a system is uncertain, but a landfall from Destin to New Orleans is probable at this juncture. Residents in these areas should closely monitor the progress of this potential system over the next several days.
Regardless of development, it appears that some locally heavy rainfall will be occurring over portions of the northeastern and northern Gulf Coast beginning in about 72 hours.
The models are not currently indicating much of a surface reflection with this feature, though they do depict it fairly well in the low- to mid-levels of the atmosphere.
Thursday, August 5, 2010
Tropical weather analysis - August 5, 2010
Tropical Storm Colin
Tropical Storm Colin managed to regenerate into a tropical cyclone this afternoon, after a reconnaissance flight confirmed the existence of a closed surface circulation. As of the 7:30 PM AST advisory from the National Hurricane Center, Colin was estimated to have maximum sustained surface winds of 60 mph, and a minimum central pressure of 1005 mb. Colin is moving NNW at 20 mph, and is located near 25.6°N 66.3°W. It's difficult to ascertain how much vertical shear the cyclone is experiencing, because the CIMSS shear product, along with many of its other products, are down for the moment. However, it is quite evident that Colin is undergoing some southwesterly vertical shear associated with an upper-level low centered to the north of the Bahamas.
Water vapor loops reveal this low quite nicely, and also indicate that it is steadily entraining dry air into the western semicircle of Colin. Infrared satellite loops suggest that Colin has an almost fully exposed surface center. This is not unexpected, given that shear is likely on the order of 20 to 30 kt at the moment. This, combined with the dry air, has ensured that Colin will generate only meager and disorganized convection, which will continue to be blown northeast, away from the center.
I expect Colin to turn to the N within the next 6-12 hours as the low- to mid-level ridge weakens further, followed by a turn to the NE or NNE by around 42 hours with an increase in forward speed as the cyclone becomes well-embedded within the southwesterly flow associated with a mid- to upper-level trough approaching from the west. Models are in generally good agreement on this. Colin could pass very close to Bermuda on Saturday.
Watches and warnings
A tropical storm warning is in effect for:
Bermuda
A tropical storm warning means that tropical storm force winds are expected within the warning area in 36 hours.
Based on the above, interests in and around Bermuda should closely monitor the progress of Colin over the next couple of days. Even if Colin doesn't come as close to the island as currently forecast, large swells will affect the island over the next couple days. The National Hurricane Center is giving Bermuda a 50% chance of receiving tropical storm force winds from Colin, and this is a reasonable forecast.
Upper-level winds are expected to remain unfavorable for significant intensification until around 24 hours, at which point they could become more favorable. By 72 hours, the shear will be near zero, and will remain that way throughout the remainder of the forecast period. Hence, I expect that Colin will attain hurricane status, and it is possible (though unlikely, IMO) that this will happen before the cyclone nears Bermuda. A hurricane watch or warning could be required for that island over the next day or so, depending upon the evolution of Colin.
I expect Colin will peak with winds of around 85 mph late on day three or early on day four. Thereafter, the cyclone will encounter sub-26C SSTs. That, combined with interaction with the aforementioned trough, should ultimately induce extratropical transition by day five. Residents along Atlantic Canada should also closely monitor the progress of Colin, even though the current NHC forecast track, as well as my own forecast, keeps the center comfortably away from that area.
Invest 93L
A vigorous tropical wave located several hundred miles west of the Cape Verde Islands is showing signs of organization. This wave was recently labeled" Invest 93L" by the National Hurricane Center. Current model consensus is for a general NW motion until around four to five days, when a turn to the N and then NE is expected as the subtropical ridge weakens further with the approach of another upper-level trough. I see no reason to disagree with this forecast for now, and I am not expecting any significant changes in the models over the next several days, as the current synoptic scale pattern favors predominant troughing along the east coast. Upper-level winds are forecast to improve in as little as 24 hours, and the 18z GFS maintains an anticyclone aloft over the system throughout much of the forecast period.
Given this, and current organization trends, I expect this wave to continue to slowly develop, becoming a tropical cyclone by 48 hours. It is possible that this system could eventually attain hurricane status.
Tropical Storm Colin managed to regenerate into a tropical cyclone this afternoon, after a reconnaissance flight confirmed the existence of a closed surface circulation. As of the 7:30 PM AST advisory from the National Hurricane Center, Colin was estimated to have maximum sustained surface winds of 60 mph, and a minimum central pressure of 1005 mb. Colin is moving NNW at 20 mph, and is located near 25.6°N 66.3°W. It's difficult to ascertain how much vertical shear the cyclone is experiencing, because the CIMSS shear product, along with many of its other products, are down for the moment. However, it is quite evident that Colin is undergoing some southwesterly vertical shear associated with an upper-level low centered to the north of the Bahamas.
Water vapor loops reveal this low quite nicely, and also indicate that it is steadily entraining dry air into the western semicircle of Colin. Infrared satellite loops suggest that Colin has an almost fully exposed surface center. This is not unexpected, given that shear is likely on the order of 20 to 30 kt at the moment. This, combined with the dry air, has ensured that Colin will generate only meager and disorganized convection, which will continue to be blown northeast, away from the center.
I expect Colin to turn to the N within the next 6-12 hours as the low- to mid-level ridge weakens further, followed by a turn to the NE or NNE by around 42 hours with an increase in forward speed as the cyclone becomes well-embedded within the southwesterly flow associated with a mid- to upper-level trough approaching from the west. Models are in generally good agreement on this. Colin could pass very close to Bermuda on Saturday.
Watches and warnings
A tropical storm warning is in effect for:
Bermuda
A tropical storm warning means that tropical storm force winds are expected within the warning area in 36 hours.
Based on the above, interests in and around Bermuda should closely monitor the progress of Colin over the next couple of days. Even if Colin doesn't come as close to the island as currently forecast, large swells will affect the island over the next couple days. The National Hurricane Center is giving Bermuda a 50% chance of receiving tropical storm force winds from Colin, and this is a reasonable forecast.
Upper-level winds are expected to remain unfavorable for significant intensification until around 24 hours, at which point they could become more favorable. By 72 hours, the shear will be near zero, and will remain that way throughout the remainder of the forecast period. Hence, I expect that Colin will attain hurricane status, and it is possible (though unlikely, IMO) that this will happen before the cyclone nears Bermuda. A hurricane watch or warning could be required for that island over the next day or so, depending upon the evolution of Colin.
I expect Colin will peak with winds of around 85 mph late on day three or early on day four. Thereafter, the cyclone will encounter sub-26C SSTs. That, combined with interaction with the aforementioned trough, should ultimately induce extratropical transition by day five. Residents along Atlantic Canada should also closely monitor the progress of Colin, even though the current NHC forecast track, as well as my own forecast, keeps the center comfortably away from that area.
Invest 93L
A vigorous tropical wave located several hundred miles west of the Cape Verde Islands is showing signs of organization. This wave was recently labeled" Invest 93L" by the National Hurricane Center. Current model consensus is for a general NW motion until around four to five days, when a turn to the N and then NE is expected as the subtropical ridge weakens further with the approach of another upper-level trough. I see no reason to disagree with this forecast for now, and I am not expecting any significant changes in the models over the next several days, as the current synoptic scale pattern favors predominant troughing along the east coast. Upper-level winds are forecast to improve in as little as 24 hours, and the 18z GFS maintains an anticyclone aloft over the system throughout much of the forecast period.
Given this, and current organization trends, I expect this wave to continue to slowly develop, becoming a tropical cyclone by 48 hours. It is possible that this system could eventually attain hurricane status.
Subscribe to:
Posts (Atom)