Eastern Atlantic tropical wave
A well-defined tropical wave located about 850 miles west-southwest of the Cape Verde Islands has become a little better organized this evening. Infrared satellite loops suggest that there is a rather concentrated area of deep convection along 8 to 9°N 32 to 33°W. There is also another area of active convection to the west of that, in the general vicinity of where ex-90L used to be.
A definite center is extremely difficult to locate tonight, even using shortwave infrared and RGB satellite animations. My best guess, which is highly uncertain, is 8N 32W. Although this system has become better organized this evening, the enormity of the cyclonic gyre with which it is embedded will likely keep any rapid consolidation to a minimum. All in all, based on CIMSS 850 mb vorticity data, this system is still poorly defined, and is embedded, as previously mentioned, in a large cyclonic gyre associated with an active ITCZ. Water vapor animations depict a large swath of very dry air just to the north of this complex weather disturbance, associated with the dry, dusty Saharan Air Layer that originates from the Sahara Desert of Africa, and gets periodically blown westward out into the Atlantic Ocean.
However, given the fact that the system will be moving generally W under the influence of a well-defined low- to mid-level tropospheric ridge, this dry air should not significantly impede development, since the steering flow will be primarily easterly, which will act to push the dry air away from the system. Latest CIMSS wind shear analysis indicates that the system is experiencing 10-20 kt of easterly to northeasterly shear, associated with a developing anticyclone just to the southwest of the Cape Verde Islands.
By about 36 hours, the system should start to gradually gain latitude and move WNW. Until then though, expect a continued W motion. By around 72 hours, a break in the Atlantic subtropical ridge is forecast to occur unanimously by all the models -- some keep it stronger, some weaker, but the general consensus is for at least a slight slackening of the south side of this ridge during this time, as a vigorous mid- to upper-level trough swings by across the mid-Atlantic states and New England.
There is still the possibility that the system could remain shallow and continue W, eventually entering the Caribbean. The NOGAPS keeps a stronger Bermuda-Azores high, which keeps the low-level flow generally easterly throughout the forecast period. This solution appears unlikely at this time, if not just for the fact that the system is likely to gradually deepen over the next couple of days.
The models are unanimously calling for tropical cyclogenesis from this feature, with the 12z CMC developing it east of the Leeward Islands in about four days. Interestingly, this particular model shows something of a Fujiwhara interaction between this system and another competing area of vorticity subsequent to this. This solution appears highly unlikely for now, but nevertheless the model has the right idea in developing this system. The 18z GFS indicates that cyclogenesis will occur right on the doorstep of the northern Leeward Islands in about four and a half days.
The 12z NOGAPS keeps the system weak, and as a consequence, it moves westward in tandem with the low-level easterly flow characteristic of the tropics. It develops it at 144 hours, while it is about 400 miles east of the central Leeward Islands. This model appears much too far south at this time, and hence I have discounted this track solution. But again, it does have the right idea with regards to eventual development from this system. Finally, the 12z ECMWF develops this system in about four days as it approaches the Leeward Islands.
Rather alarmingly, both the GFS and ECMWF foresee the synoptic scale pattern as being supportive of a stronger Atlantic subtropical ridge, strong enough to prevent the system from recurving harmlessly out to sea. While I do not like to speculate on long-range tracks, particularly with systems that do not even have a definite surface center, I am inclined to go with the solution provided by these models, based on the current large-scale pattern over North America.
Upper-level winds support continued slow development of this disturbance. I am not expecting any rapid development, however, and the NHC's current forecast of a 40% chance of tropical cyclogenesis occurring in 48 hours is a reasonable one. The earliest I would expect this system to become a tropical depression or tropical storm is Tuesday night, but more likely Wednesday afternoon.
Central Caribbean tropical wave
A tropical wave moving across the central Caribbean Sea continues to sporadically produce limited and disorganized shower activity. Upper-level winds are not conducive for development in this area, and are forecast to continue being largely zonal and strong, even as the system approaches Central America in about two days. I am not expecting any significant development of this wave, though it may bring heavy rains to Honduras, Nicaragua, El Salvador, and Costa Rica over the next couple of days as it continues moving generally W.
Saturday, July 31, 2010
Friday, July 30, 2010
Tropical weather analysis - July 30, 2010
Invest 90L
A strong tropical wave, dubbed "Invest 90L" by the National Hurricane Center, has become less organized throughout today. This isn't due to unfavorable atmospheric conditions. Rather, it is due to interaction with a larger tropical wave to the east, near the Cape Verde Islands. I suspect that this wave will continue to gradually ingest Invest 90L, and will likely be designated "Invest 91L" tomorrow morning. This system is very poorly organized, with shortwave infrared satellite animations indicating very little in the way of shower activity, much less any cyclonic vorticity. I can detect a faint, very weak and rapidly dissipating spin from 8 to 9°N and along 34 to 32°W. The rest of the convection in the area is associated primarily with the ITCZ, not the wave.
Latest CIMSS wind shear analysis from University of Wisconsin CIMSS depicts only 5-10 kt of northeasterly shear impinging upon the system. However, again, because of dangerously close proximity to the aforementioned tropical wave to the east, I am not expecting significant development of Invest 90L. Obviously though, it would be rather foolhardy for anyone to take their eyes off the system until the system completely loses its identity.
The Cape Verde wave should move W over the next couple of days, with a more WNW motion occurring in 60-72 hours as a shortwave trough weakens the ridge to the north. This system may pass north of the Leeward Islands and Puerto Rico in about five to seven days, but it is uncertain if this system will be able to recurve out to sea entirely. This system may be a long-range threat to the southeast or northeastern United States, but this is highly speculative, and residents living in those areas should not be overly concerned. Upper-level winds favor development over the next several days, but as the wave approaches the Lesser Antilles, strong westerly shear associated with the TUTT will return once again, which will make additional development or intensification highly improbable, and the system may even destroyed at that point.
Should it remain farther south, however, and enter the Caribbean, upper-level winds greatly favor intensification.
Eastern Caribbean tropical wave
A tropical wave located across the eastern Caribbean Sea continues to produce disorganized convection. Upper-level winds are currently unfavorable for development. This, along with the wave's fast forward speed, 20 to 25 mph (which is expected to continue for the next couple days, by the way), should prevent any appreciable organization from occurring until the system nears Central America in about two to three days. At that point, upper-level winds will also relax, and the system will have a small window of opportunity in which to become a tropical cyclone. I am not expecting this to happen, however.
Also, I still fully anticipate an active season. I cannot stress this enough. This season will be active -- in 1998, the most similar year to this one that I can find, the second named storm did not occur until August 20. That season ended up producing 14 named storms, 10 hurricanes, and 3 major hurricanes, and, most remarkably, four simultaneous hurricanes existed in the basin on September 25 -- Georges, Ivan, Jeanne, and Karl. The season also had three hurricanes impact the United States mainland: Bonnie, Earl, and Georges.
Lastly, it featured the mighty Hurricane Mitch, which killed anywhere from 11 to 20,000 people across portions of Central America due to days of prolonged torrential rainfall, which produced flash flooding and mudslides across mountainous areas.
While I'm not saying we're necessarily going to see an exact repeat of 1998, I do not want anyone to be foolish enough to drop their guard by thinking that the season is over. Most parameters still point to a sharp upswing in overall activity beginning the second week of August.
A strong tropical wave, dubbed "Invest 90L" by the National Hurricane Center, has become less organized throughout today. This isn't due to unfavorable atmospheric conditions. Rather, it is due to interaction with a larger tropical wave to the east, near the Cape Verde Islands. I suspect that this wave will continue to gradually ingest Invest 90L, and will likely be designated "Invest 91L" tomorrow morning. This system is very poorly organized, with shortwave infrared satellite animations indicating very little in the way of shower activity, much less any cyclonic vorticity. I can detect a faint, very weak and rapidly dissipating spin from 8 to 9°N and along 34 to 32°W. The rest of the convection in the area is associated primarily with the ITCZ, not the wave.
Latest CIMSS wind shear analysis from University of Wisconsin CIMSS depicts only 5-10 kt of northeasterly shear impinging upon the system. However, again, because of dangerously close proximity to the aforementioned tropical wave to the east, I am not expecting significant development of Invest 90L. Obviously though, it would be rather foolhardy for anyone to take their eyes off the system until the system completely loses its identity.
The Cape Verde wave should move W over the next couple of days, with a more WNW motion occurring in 60-72 hours as a shortwave trough weakens the ridge to the north. This system may pass north of the Leeward Islands and Puerto Rico in about five to seven days, but it is uncertain if this system will be able to recurve out to sea entirely. This system may be a long-range threat to the southeast or northeastern United States, but this is highly speculative, and residents living in those areas should not be overly concerned. Upper-level winds favor development over the next several days, but as the wave approaches the Lesser Antilles, strong westerly shear associated with the TUTT will return once again, which will make additional development or intensification highly improbable, and the system may even destroyed at that point.
Should it remain farther south, however, and enter the Caribbean, upper-level winds greatly favor intensification.
Eastern Caribbean tropical wave
A tropical wave located across the eastern Caribbean Sea continues to produce disorganized convection. Upper-level winds are currently unfavorable for development. This, along with the wave's fast forward speed, 20 to 25 mph (which is expected to continue for the next couple days, by the way), should prevent any appreciable organization from occurring until the system nears Central America in about two to three days. At that point, upper-level winds will also relax, and the system will have a small window of opportunity in which to become a tropical cyclone. I am not expecting this to happen, however.
Also, I still fully anticipate an active season. I cannot stress this enough. This season will be active -- in 1998, the most similar year to this one that I can find, the second named storm did not occur until August 20. That season ended up producing 14 named storms, 10 hurricanes, and 3 major hurricanes, and, most remarkably, four simultaneous hurricanes existed in the basin on September 25 -- Georges, Ivan, Jeanne, and Karl. The season also had three hurricanes impact the United States mainland: Bonnie, Earl, and Georges.
Lastly, it featured the mighty Hurricane Mitch, which killed anywhere from 11 to 20,000 people across portions of Central America due to days of prolonged torrential rainfall, which produced flash flooding and mudslides across mountainous areas.
While I'm not saying we're necessarily going to see an exact repeat of 1998, I do not want anyone to be foolish enough to drop their guard by thinking that the season is over. Most parameters still point to a sharp upswing in overall activity beginning the second week of August.
Thursday, July 29, 2010
Tropical weather analysis - July 29, 2010
Invest 90L
A large but well-defined perturbation in the Intertropical Convergence Zone (ITCZ) was designated Invest 90L this afternoon by the National Hurricane Center. Visible satellite animations suggest that this system is embedded within a large area of convection and cyclonic vorticity associated with the ITCZ. My best estimate for a "center" position, based on satellite data, is 7N 31W. Latest CIMSS 850 mb vorticity data also somewhat supports this.
Upper-level winds are favorable for additional development of this system, with CIMSS wind shear analysis indicating only 5-10 kt of east to northeasterly shear over the system. This favorable upper-level environment is forecast to persist throughout the next several days, with a fairly uniform easterly flow. The two largest impediments I can see for 90L is the large amount of dry air to the north, depicted rather nicely on water vapor loops, and the broad cyclonic gyre that the system is embedded in. However, given the very moist environment within the vicinity of the disturbance, along with the fact that the system should move generally W over the next couple of days, I am not expecting the dry air to completely halt any additional development of 90L.
Analysis of 12z steering from PSU's e-wall suggests that a break in the Atlantic subtropical ridge could occur in about 60-72 hours as a mid- to upper-level trough swings by to the north of the system. However, unless 90L develops significantly during the next three days, this weakness should not be strong enough to turn the system poleward so much so that it completely misses any and all land areas.
All of that having been said, I expect some slow additional development of the disturbance as it moves generally W over the next couple of days. As previously noted, a turn to the WNW could occur in 60-72 hours as the subtropical ridge weakens somewhat. The 18z GFS develops this system just north of Puerto Rico in 168 hours. The 12z CMC develops this in as little as two and a half to three days, and eventually makes it a hurricane. However, such rapid development does not appear likely at this time, and I am discounting both the track and intensity solution currently being provided by this model. Finally, the 12z ECMWF hints at tropical cyclogenesis occurring north of the Leeward Islands in about six days, but quickly loses the system as it moves it WNW toward the southeast United States coast.
I would not expect development to begin occurring in earnest until around 60 hours, as the system begins to gain some latitude. The National Hurricane Center is giving 90L a 20% chance of becoming a tropical cyclone within the next 48 hours, and this is a reasonable forecast.
Windward Islands tropical wave
A tropical wave is producing scattered showers and thunderstorms across portions of the Windward Islands and adjacent eastern Caribbean Sea.
However, the wave axis has not yet passed these islands. Upper-level winds are currently not favorable for development, but could become more favorable over the next several days as the wave moves generally W, well-embedded within the low-level easterly trade wind flow common of the tropics. Surface observations from the Windward Islands, along with buoy data, indicate that nothing of note is occurring at the surface in association with this wave.
I suspect that any development will be very slow to occur. And, though the upper wind flow may improve somewhat over the next several days, the system will run into Central America in about four to five days.
Regardless of development, locally heavy rainfall and strong gusty winds will accompany the wave as it passes through the Windward Islands tonight. None of the models, save the CMC, which is always too bullish with tropical cyclogenesis, significantly develop the wave.
A large but well-defined perturbation in the Intertropical Convergence Zone (ITCZ) was designated Invest 90L this afternoon by the National Hurricane Center. Visible satellite animations suggest that this system is embedded within a large area of convection and cyclonic vorticity associated with the ITCZ. My best estimate for a "center" position, based on satellite data, is 7N 31W. Latest CIMSS 850 mb vorticity data also somewhat supports this.
Upper-level winds are favorable for additional development of this system, with CIMSS wind shear analysis indicating only 5-10 kt of east to northeasterly shear over the system. This favorable upper-level environment is forecast to persist throughout the next several days, with a fairly uniform easterly flow. The two largest impediments I can see for 90L is the large amount of dry air to the north, depicted rather nicely on water vapor loops, and the broad cyclonic gyre that the system is embedded in. However, given the very moist environment within the vicinity of the disturbance, along with the fact that the system should move generally W over the next couple of days, I am not expecting the dry air to completely halt any additional development of 90L.
Analysis of 12z steering from PSU's e-wall suggests that a break in the Atlantic subtropical ridge could occur in about 60-72 hours as a mid- to upper-level trough swings by to the north of the system. However, unless 90L develops significantly during the next three days, this weakness should not be strong enough to turn the system poleward so much so that it completely misses any and all land areas.
All of that having been said, I expect some slow additional development of the disturbance as it moves generally W over the next couple of days. As previously noted, a turn to the WNW could occur in 60-72 hours as the subtropical ridge weakens somewhat. The 18z GFS develops this system just north of Puerto Rico in 168 hours. The 12z CMC develops this in as little as two and a half to three days, and eventually makes it a hurricane. However, such rapid development does not appear likely at this time, and I am discounting both the track and intensity solution currently being provided by this model. Finally, the 12z ECMWF hints at tropical cyclogenesis occurring north of the Leeward Islands in about six days, but quickly loses the system as it moves it WNW toward the southeast United States coast.
I would not expect development to begin occurring in earnest until around 60 hours, as the system begins to gain some latitude. The National Hurricane Center is giving 90L a 20% chance of becoming a tropical cyclone within the next 48 hours, and this is a reasonable forecast.
Windward Islands tropical wave
A tropical wave is producing scattered showers and thunderstorms across portions of the Windward Islands and adjacent eastern Caribbean Sea.
However, the wave axis has not yet passed these islands. Upper-level winds are currently not favorable for development, but could become more favorable over the next several days as the wave moves generally W, well-embedded within the low-level easterly trade wind flow common of the tropics. Surface observations from the Windward Islands, along with buoy data, indicate that nothing of note is occurring at the surface in association with this wave.
I suspect that any development will be very slow to occur. And, though the upper wind flow may improve somewhat over the next several days, the system will run into Central America in about four to five days.
Regardless of development, locally heavy rainfall and strong gusty winds will accompany the wave as it passes through the Windward Islands tonight. None of the models, save the CMC, which is always too bullish with tropical cyclogenesis, significantly develop the wave.
Monday, July 26, 2010
Louisiana hurricane history Part 3b: Unnamed hurricane (Sep 11 - Sep 16)
This storm was the second in a series of three powerful hurricanes to make landfall in southeastern Louisiana during the 1860 Atlantic hurricane season. This system was first noted in the early morning hours of September 11 about 150 miles west-northwest of the Dry Tortugas. It made landfall on the morning of September 16 near the Mouth of the Mississippi River along the southwest end of Plaquemines Parish.
Storm history
As mentioned above, a Category 2 hurricane was first detected about 150 miles west-northwest of the Dry Tortugas near the Florida Keys, moving W. As with most systems in the 1800s, the complete history of this hurricane is not known. It is possible that the system moved in from the Bahamas and south Florida, but this presents a problem: why was such an impact not recorded, even during those technologically scarce times? The only possible explanation to this is that the system was only a tropical depression or tropical storm whilst traversing these regions, and it did not intensify significantly until it reached the eastern Gulf of Mexico. At that point though, rapid intensification would have had to have occurred in order for the storm to go from a tropical depression/storm to a Category 2 hurricane within the span of just a day or so. Another possibility is that the system was moving northward from the western Caribbean, across western Cuba, and then into the Gulf of Mexico before a ridge built back in to the north. However, this would be a rather atypical motion for the middle of September, and in fact, more typical of the middle of October.
Regardless of its origin, the hurricane continued generally westward as a Category 2 until the morning of September 12, at which point it turned to the west-northwest as the subtropical ridge to the north weakened somewhat, likely due to the approach of a mid-latitude trough from the west. The hurricane turned to the northwest late on the afternoon of September 13 as it encountered a further weakness in the aforementioned ridge. Around 24 hours later, the hurricane turned northward, now well-embedded within the southerly flow along the western periphery of the subtropical ridge, and the aforementioned trough and its associated cold front to the west. The hurricane made landfall across lower Plaquemines Parish at 0600 GMT September 15, then turned further poleward, to the north-northeast, at around 1200 GMT that same day. At this time, the hurricane is still estimated to have been a Category 2, located just offshore the southwestern coast of Mississippi. The hurricane quickly made a second landfall near Bay St. Louis, still a Category 2.
The hurricane continued north-northeastward under the influence from the trough, and ultimately dissipated somewhere over the eastern United States. It was last identified as a 45 kt (50 mph) tropical storm at 0600 GMT near 33.0°N 88.0°W, still moving quickly north-northeastward under the influence of the climatological mid-latitude westerlies.
Figure 1. Track of the hurricane.
Louisiana
Gale force winds were reported for around 20 hours across extreme southeast Louisiana as the hurricane ravaged the area. Additionally, and quite rare in a tropical cyclone, hail was reported. The only other tropical cyclone I can think of that has produced hail (though there were undoubtedly others as well) is 1995's Hurricane Marilyn.
Every building in Balize, an old settlement located about five miles from Pillottown, (the latter of which is located along extreme lower Plaquemines Parish, on the southeast side facing the Gulf), was destroyed by the hurricane, and the third Bayou St. John lighthouse was damaged beyond repair.
A storm surge in excess of several feet was reported across lower Plaquemines Parish, which inundated the area and killed several people. The tied was reported as being six feet above the high tide. All wharves along the southern shore of Lake Pontchartrain were destroyed.
Mississippi
Across Mississippi, where the hurricane's second landfall occurred, a lighthouse in the area, along with a hotel, were swept away by the storm surge.
Total damages from the hurricane exceeded $1 million.
Storm history
As mentioned above, a Category 2 hurricane was first detected about 150 miles west-northwest of the Dry Tortugas near the Florida Keys, moving W. As with most systems in the 1800s, the complete history of this hurricane is not known. It is possible that the system moved in from the Bahamas and south Florida, but this presents a problem: why was such an impact not recorded, even during those technologically scarce times? The only possible explanation to this is that the system was only a tropical depression or tropical storm whilst traversing these regions, and it did not intensify significantly until it reached the eastern Gulf of Mexico. At that point though, rapid intensification would have had to have occurred in order for the storm to go from a tropical depression/storm to a Category 2 hurricane within the span of just a day or so. Another possibility is that the system was moving northward from the western Caribbean, across western Cuba, and then into the Gulf of Mexico before a ridge built back in to the north. However, this would be a rather atypical motion for the middle of September, and in fact, more typical of the middle of October.
Regardless of its origin, the hurricane continued generally westward as a Category 2 until the morning of September 12, at which point it turned to the west-northwest as the subtropical ridge to the north weakened somewhat, likely due to the approach of a mid-latitude trough from the west. The hurricane turned to the northwest late on the afternoon of September 13 as it encountered a further weakness in the aforementioned ridge. Around 24 hours later, the hurricane turned northward, now well-embedded within the southerly flow along the western periphery of the subtropical ridge, and the aforementioned trough and its associated cold front to the west. The hurricane made landfall across lower Plaquemines Parish at 0600 GMT September 15, then turned further poleward, to the north-northeast, at around 1200 GMT that same day. At this time, the hurricane is still estimated to have been a Category 2, located just offshore the southwestern coast of Mississippi. The hurricane quickly made a second landfall near Bay St. Louis, still a Category 2.
The hurricane continued north-northeastward under the influence from the trough, and ultimately dissipated somewhere over the eastern United States. It was last identified as a 45 kt (50 mph) tropical storm at 0600 GMT near 33.0°N 88.0°W, still moving quickly north-northeastward under the influence of the climatological mid-latitude westerlies.
Figure 1. Track of the hurricane.
Louisiana
Gale force winds were reported for around 20 hours across extreme southeast Louisiana as the hurricane ravaged the area. Additionally, and quite rare in a tropical cyclone, hail was reported. The only other tropical cyclone I can think of that has produced hail (though there were undoubtedly others as well) is 1995's Hurricane Marilyn.
Every building in Balize, an old settlement located about five miles from Pillottown, (the latter of which is located along extreme lower Plaquemines Parish, on the southeast side facing the Gulf), was destroyed by the hurricane, and the third Bayou St. John lighthouse was damaged beyond repair.
A storm surge in excess of several feet was reported across lower Plaquemines Parish, which inundated the area and killed several people. The tied was reported as being six feet above the high tide. All wharves along the southern shore of Lake Pontchartrain were destroyed.
Mississippi
Across Mississippi, where the hurricane's second landfall occurred, a lighthouse in the area, along with a hotel, were swept away by the storm surge.
Total damages from the hurricane exceeded $1 million.
Friday, July 23, 2010
Tropical weather analysis - July 23, 2010
Bonnie
Bonnie weakened to a tropical depression while traversing southern Florida this afternoon. Thelast of the visible satellite images place the center at 26N 83W, over the eastern Gulf of Mexico. The National Hurricane Center had it at 26.4N 82.5W just a little over an hour ago, so this motion merely serves to reflect an extrapolation of that position. In any case, the aforementioned imagery also reveals a highly disorganized tropical cyclone, with the small area of deep convection displaced to the north and northwest of the poorly defined surface center, which appears to be located about 40-50 miles southeast of the aforementioned, shapeless convective activity.
This extreme disorganization is due to strong southeasterly vertical wind shear in excess of 30 kt. This shear is associated with a large, persistent, and powerful upper-level low centered near 27N 93W, and a large and powerful upper-level ridge centered across the mid-Atlantic states. Bottom line? Bonnie is embedded within a very hostile environment for intensification, with water vapor imagery depicting a large swath of dry air to the west. This dry air is gradually being entrained into the poorly defined surface center due to clockwise flow around the aforementioned ridge. Given the noticeable lack of upper-level divergence and low-level convergence associated with the cyclone, along with the aforementioned dry air and a continued hostile upper wind environment, I am not expecting Bonnie to be able to intensify. In fact, the most likely scenario is for the system to gradually weaken, ultimately opening up into a disorganized trough of low pressure prior to moving ashore along the northern Gulf Coast in the next 24-36 hours.
The track forecast is rather straightforward. Water vapor imagery depicts a strong and solid southeasterly flow impinging upon the cyclone. Embedded within general southeasterly flow between the upper low and the aforementioned anticyclone, Bonnie should continue moving WNW for the next 12 hours or so, after which point a turn to the NW should occur. By this time, a weakness should become apparent within the western Atlantic subtropical ridge as a mid- to upper-level trough and its associated cold front will be nudged a bit to the southeast by a well-defined upper-level low currently moving across northwestern North Dakota. This should effectively erode the ridge and allow the cyclone to turn more poleward during this time. That motion should continue until well after landfall occurs along the northern Gulf Coast in about 24-30 hours, and the cyclone could still be moving NW as it enters eastern or central Arkansas in about 60 hours.
The intensity forecast is also relatively simple. The 18z GFS indicates that the current southeasterly flow will gradually veer to the northeast, associated with the aforementioned ridge. There could be a brief relaxation of the shear over the next six hours, as indicated by the GFS, and then again in 30 hours as the system approaches the northern Gulf Coast. I'm in general agreement with the NHC's 5:00 PM EDT forecast track, albeit slightly farther to the right when landfall occurs. I expect that landfall will occur along the Louisiana/Mississippi border in just around 30 hours.
Watches and warnings
A tropical storm warning is in effect from:
- Destin, Florida to Morgan City, Louisiana, including New Orleans and Lake Pontchartrain
However, I imagine that these warnings were given as a course of least regret, just in case the cyclone unexpectedly strengthens due to an unforeseen relaxation of the vertical shear. I am not actually expecting tropical storm force winds anywhere within the warning area. I still expect Bonnie to open into an elongated trough within the next 12 hours, given the hostile environment.
Bonnie's main legacy will be 4 to 6 foot waves atop the oil spill region. A persistent fetch of SE to E winds will begin to blow across that region beginning in about 12 hours. This could potentially bring oil into the already devastated Louisiana marshlands, along with other areas of coast that have already experienced oil on their shores.
Elsewhere
There are no other threat areas to discuss in the tropics at the moment. Former Invest 98L moved inland near Tampico early this morning. A weak area of low pressure could still form near the Cape Verde Islands on Sunday, as indicated by both the GFS and the ECMWF, but both, particularly the latter, have become far less aggressive in this forecast than they were previously. The ECMWF brings this system off Africa at a higher latitude than the GFS does. I am inclined to agree with the solution of the GFS, given current convective trends over western Africa. Though upper-level winds favor development in this area, a dry environment awaits the system in the eastern Atlantic, which will act to inhibit any significant development. In fact, this is probably why the aforementioned models do not strengthen this feature, and quickly lose it within 12 hours of exiting the coast.
It should be noted that we are forecast, as per the EWP model, to enter a rather dry period across the Atlantic basin as the downward motion pulse of the MJO -- a 30 to 60 day eastward propagation of moisture originating over the Indian Ocean. The upward MJO pulse tends to favor greater atmospheric instability, and hence, enhances convection. The downward motion tends to do the exact opposite. However, tropical cyclogenesis can still occur during downward MJO pulses -- for instance, 2005's Harvey and Irene all formed during the downward MJO, the latter of which ultimately became a Category 2 hurricane that threatened the Carolinas.
However, given that the upward MJO has been rather hesitant to leave our area throughout most of the season, I rather am skeptical of the EWP's forecast. We will see, though.
On the other hand, the CFS model foresees a far less robust and long-lasting downward pulse.
Finally, the GFS is forecasting a rather significant downward MJO pulse, but an extrapolation of this forecast points to a general lessening of this motion by the second week of August. I rather like the forecast from the CFS, given current convective trends across the basin. However, given that both the EWP and the GFS are forecasting a significant downward pulse, I cannot simply ignore them. Hence, I will split the difference and forecast a downward MJO pulse for the next two weeks, after which point we should return to a neutral MJO pulse, followed by an upward motion pulse sometime during the second week of August.
Remember, just because we have only seen one significant tropical cyclone this year: Alex, doesn't mean that the season is a bust. Please do not be lulled into a false sense of security. In 1998, the most similar analog I can think of, the second storm didn't develop until August 19, and we ended up having 14 named storms, 10 hurricanes, and 3 major hurricanes that season, including notable ones like Bonnie, Georges, and Mitch.
The season isn't over by a longshot, and I still fully anticipate an above average season, even if we don't necessarily end up getting the 18 storms that CSU predicts.
Bonnie weakened to a tropical depression while traversing southern Florida this afternoon. Thelast of the visible satellite images place the center at 26N 83W, over the eastern Gulf of Mexico. The National Hurricane Center had it at 26.4N 82.5W just a little over an hour ago, so this motion merely serves to reflect an extrapolation of that position. In any case, the aforementioned imagery also reveals a highly disorganized tropical cyclone, with the small area of deep convection displaced to the north and northwest of the poorly defined surface center, which appears to be located about 40-50 miles southeast of the aforementioned, shapeless convective activity.
This extreme disorganization is due to strong southeasterly vertical wind shear in excess of 30 kt. This shear is associated with a large, persistent, and powerful upper-level low centered near 27N 93W, and a large and powerful upper-level ridge centered across the mid-Atlantic states. Bottom line? Bonnie is embedded within a very hostile environment for intensification, with water vapor imagery depicting a large swath of dry air to the west. This dry air is gradually being entrained into the poorly defined surface center due to clockwise flow around the aforementioned ridge. Given the noticeable lack of upper-level divergence and low-level convergence associated with the cyclone, along with the aforementioned dry air and a continued hostile upper wind environment, I am not expecting Bonnie to be able to intensify. In fact, the most likely scenario is for the system to gradually weaken, ultimately opening up into a disorganized trough of low pressure prior to moving ashore along the northern Gulf Coast in the next 24-36 hours.
The track forecast is rather straightforward. Water vapor imagery depicts a strong and solid southeasterly flow impinging upon the cyclone. Embedded within general southeasterly flow between the upper low and the aforementioned anticyclone, Bonnie should continue moving WNW for the next 12 hours or so, after which point a turn to the NW should occur. By this time, a weakness should become apparent within the western Atlantic subtropical ridge as a mid- to upper-level trough and its associated cold front will be nudged a bit to the southeast by a well-defined upper-level low currently moving across northwestern North Dakota. This should effectively erode the ridge and allow the cyclone to turn more poleward during this time. That motion should continue until well after landfall occurs along the northern Gulf Coast in about 24-30 hours, and the cyclone could still be moving NW as it enters eastern or central Arkansas in about 60 hours.
The intensity forecast is also relatively simple. The 18z GFS indicates that the current southeasterly flow will gradually veer to the northeast, associated with the aforementioned ridge. There could be a brief relaxation of the shear over the next six hours, as indicated by the GFS, and then again in 30 hours as the system approaches the northern Gulf Coast. I'm in general agreement with the NHC's 5:00 PM EDT forecast track, albeit slightly farther to the right when landfall occurs. I expect that landfall will occur along the Louisiana/Mississippi border in just around 30 hours.
Watches and warnings
A tropical storm warning is in effect from:
- Destin, Florida to Morgan City, Louisiana, including New Orleans and Lake Pontchartrain
However, I imagine that these warnings were given as a course of least regret, just in case the cyclone unexpectedly strengthens due to an unforeseen relaxation of the vertical shear. I am not actually expecting tropical storm force winds anywhere within the warning area. I still expect Bonnie to open into an elongated trough within the next 12 hours, given the hostile environment.
Bonnie's main legacy will be 4 to 6 foot waves atop the oil spill region. A persistent fetch of SE to E winds will begin to blow across that region beginning in about 12 hours. This could potentially bring oil into the already devastated Louisiana marshlands, along with other areas of coast that have already experienced oil on their shores.
Elsewhere
There are no other threat areas to discuss in the tropics at the moment. Former Invest 98L moved inland near Tampico early this morning. A weak area of low pressure could still form near the Cape Verde Islands on Sunday, as indicated by both the GFS and the ECMWF, but both, particularly the latter, have become far less aggressive in this forecast than they were previously. The ECMWF brings this system off Africa at a higher latitude than the GFS does. I am inclined to agree with the solution of the GFS, given current convective trends over western Africa. Though upper-level winds favor development in this area, a dry environment awaits the system in the eastern Atlantic, which will act to inhibit any significant development. In fact, this is probably why the aforementioned models do not strengthen this feature, and quickly lose it within 12 hours of exiting the coast.
It should be noted that we are forecast, as per the EWP model, to enter a rather dry period across the Atlantic basin as the downward motion pulse of the MJO -- a 30 to 60 day eastward propagation of moisture originating over the Indian Ocean. The upward MJO pulse tends to favor greater atmospheric instability, and hence, enhances convection. The downward motion tends to do the exact opposite. However, tropical cyclogenesis can still occur during downward MJO pulses -- for instance, 2005's Harvey and Irene all formed during the downward MJO, the latter of which ultimately became a Category 2 hurricane that threatened the Carolinas.
However, given that the upward MJO has been rather hesitant to leave our area throughout most of the season, I rather am skeptical of the EWP's forecast. We will see, though.
On the other hand, the CFS model foresees a far less robust and long-lasting downward pulse.
Finally, the GFS is forecasting a rather significant downward MJO pulse, but an extrapolation of this forecast points to a general lessening of this motion by the second week of August. I rather like the forecast from the CFS, given current convective trends across the basin. However, given that both the EWP and the GFS are forecasting a significant downward pulse, I cannot simply ignore them. Hence, I will split the difference and forecast a downward MJO pulse for the next two weeks, after which point we should return to a neutral MJO pulse, followed by an upward motion pulse sometime during the second week of August.
Remember, just because we have only seen one significant tropical cyclone this year: Alex, doesn't mean that the season is a bust. Please do not be lulled into a false sense of security. In 1998, the most similar analog I can think of, the second storm didn't develop until August 19, and we ended up having 14 named storms, 10 hurricanes, and 3 major hurricanes that season, including notable ones like Bonnie, Georges, and Mitch.
The season isn't over by a longshot, and I still fully anticipate an above average season, even if we don't necessarily end up getting the 18 storms that CSU predicts.
Thursday, July 22, 2010
Tropical weather analysis - July 22, 2010
Tropical Depression Three
A vigorous tropical wave located across the Turks and Caicos Islands, previously labeled Invest 97L by the National Hurricane Center, has organized into Tropical Depression Three.
Visible satellite animations confirm what the National Hurricane Center has said, a closed surface circulation is clearly evident. The partially exposed center of the newly developed depression isn't particularly difficult to locate, and the NHC puts it at 21.9N 75.0W. In addition, the maximum sustained winds are estimated to be near 35 mph. A reconnaissance aircraft will investigate the cyclone later today and give us a better assessment of the intensity of the system. The NHC has the motion estimated at WNW/15 mph, and satellite loops agree quite well with this.
The cyclone is still in its formative stages, and as a result, is not well organized. However, it is steadily improving as the upper flow slowly abates with the westward retreat of the persistent upper-level low that has been vehemently shearing the system (and still is, to a degree) over the last several days. Indeed, analysis of vorticity data from University of Wisconsin CIMSS suggests that the low- and mid-level centers have become more symmetrically aligned in the vertical, further confirming a gradual reduction in the vertical wind shear. Visible satellite imagery indicates that the center is located near the western edge of the deep convective mass, and the imagery also reveals less of a shearing pattern than it did just two hours ago.
Additionally, high arc clouds are streaming toward the center, rather than away from it as was previously the case. This indicates that the overall circulation is slowly becoming better defined.
Water vapor animations, used in conjunction with visible satellite loops, strongly suggest that the aforementioned upper low is moving faster than TD3. In fact, it may soon move far enough away to ventilate it, thereby generating a poleward upper-level outflow channel. Should this occur, it will assist in quicker intensification prior to the system reaching south Florida or the Florida Keys in about 18 hours or so. The depression is currently traversing very warm Sea Surface Temperatures (SSTs) of 29-30°C, well above the minimum threshold of 26C typically needed for tropical cyclogenesis.
Additionally, the cyclone is poised to traverse an area of increased oceanic heat content across the central Bahamas within the next six hours or so, which will assist in the intensification process.
Rather interestingly, latest analysis from CIMSS indicates the beginnings of an upper-level anticyclone, which is currently centered about 50 miles to the southeast of the depression. No doubt, this development has occurred because of the rapidly lessening influence of the persistent upper low. The 6z GFS suggests that this anticyclone will remain collocated with TD3 for at least the next 18 hours, after which point it is forecast to detach from the cyclone and retreat northeastward and gradually open, ultimately becoming absorbed into the western Atlantic subtropical ridge. My current thinking is that the anticyclone will benefit the depression enough to bring it to 45 mph before it approaches southern Florida or the keys. Obviously, the intensity could certainly be higher than this, depending on how well-established, persistent, and strong the anticyclone becomes.
The system, should it go through the Florida Straits, rather than through south Florida, should emerge into the eastern Gulf of Mexico in around 24 hours. Upper-level winds are not forecast to be ideal for intensification, and may only be marginally favorable. However, the shear will primarily be southerly, which would tend to have less of an impact on the cyclone than it ordinarily would. Overall, atmospheric and oceanic conditions conditions appear favorable enough for a 65 mph tropical storm, but this will depend upon the evolution of the upper wind environment across the Gulf.
A large weakness is evident in the subtropical ridge to the north of the cyclone, which is responsible for the current WNW motion. I expect this general motion to continue throughout most of the forecast period, though a more poleward turn could occur by around 60 hours as the system nears the coast of central Louisiana. Just how much of a poleward turn this system takes will depend largely upon the evolution of the aforementioned upper low, which is forecast to continue retreating westward into the Gulf, and eventually move inland by around 54 hours. This is impossible to tell at this point, so residents from Galveston eastward to Biloxi should carefully monitor the progress of this system over the next several days. Another factor regarding the eventual Gulf Coast landfall location of the depression will depend upon a cold front currently moving across the central United States.
My current thinking is that this trough and associated front will at least dent the western extent of the Atlantic subtropical ridge during the next two days. All in all, based upon model analysis as well as other data, I expect the cyclone to ultimately make landfall along the west-central Louisiana coast, just west of Vermilion Bay, though this is obviously not certain. Again, residents across the aforementioned areas should closely monitor the progress of this system over the coming days.
My forecast track agrees well with the NHC's current one, except it's just a little bit to the east.
Invest 98L
Invest 98L continues churning across the Bay of Campeche. Visible satellite animations imply the continued development of deep convection near the center, with some bands of heavy thunderstorms to the north of the circulation. These rains are impacting portions of central Mexico to the south of Tampico, an area just recently battered by Hurricane Alex and Tropical Depression Two. Based on animation of visible satellite imagery and 850 mb vorticity data from CIMSS, I assume that the surface center is located near 20N 95W. An upper-level anticyclone continues to be centered aloft, which favors continued development until the system moves inland. Land interaction is the only inhibiting factor I can see to tropical cyclogenesis, and the system should move inland to the south of Tampico by tonight or early tomorrow morning. The farther south this system goes, the less time it will have over water.
I give this system a 50% chance of becoming a tropical depression prior to moving inland. Were it not for land interaction, I'd go higher. Residents from Veracruz to Tampico should closely monitor the progress of this system. Regardless of development, locally heavy rainfall will overspread the aforementioned areas, and possibly even extreme southern Texas over the next day or two.
Elsewhere
The 12z ECMWF isn't out yet, but the 0z run was still indicating the possibility of our first Cape Verde storm on July 25. The 6z GFS also continues to reflect this possibility. Upper-level winds still appear rather conducive for anything that might happen to form in this area.
A vigorous tropical wave located across the Turks and Caicos Islands, previously labeled Invest 97L by the National Hurricane Center, has organized into Tropical Depression Three.
Visible satellite animations confirm what the National Hurricane Center has said, a closed surface circulation is clearly evident. The partially exposed center of the newly developed depression isn't particularly difficult to locate, and the NHC puts it at 21.9N 75.0W. In addition, the maximum sustained winds are estimated to be near 35 mph. A reconnaissance aircraft will investigate the cyclone later today and give us a better assessment of the intensity of the system. The NHC has the motion estimated at WNW/15 mph, and satellite loops agree quite well with this.
The cyclone is still in its formative stages, and as a result, is not well organized. However, it is steadily improving as the upper flow slowly abates with the westward retreat of the persistent upper-level low that has been vehemently shearing the system (and still is, to a degree) over the last several days. Indeed, analysis of vorticity data from University of Wisconsin CIMSS suggests that the low- and mid-level centers have become more symmetrically aligned in the vertical, further confirming a gradual reduction in the vertical wind shear. Visible satellite imagery indicates that the center is located near the western edge of the deep convective mass, and the imagery also reveals less of a shearing pattern than it did just two hours ago.
Additionally, high arc clouds are streaming toward the center, rather than away from it as was previously the case. This indicates that the overall circulation is slowly becoming better defined.
Water vapor animations, used in conjunction with visible satellite loops, strongly suggest that the aforementioned upper low is moving faster than TD3. In fact, it may soon move far enough away to ventilate it, thereby generating a poleward upper-level outflow channel. Should this occur, it will assist in quicker intensification prior to the system reaching south Florida or the Florida Keys in about 18 hours or so. The depression is currently traversing very warm Sea Surface Temperatures (SSTs) of 29-30°C, well above the minimum threshold of 26C typically needed for tropical cyclogenesis.
Additionally, the cyclone is poised to traverse an area of increased oceanic heat content across the central Bahamas within the next six hours or so, which will assist in the intensification process.
Rather interestingly, latest analysis from CIMSS indicates the beginnings of an upper-level anticyclone, which is currently centered about 50 miles to the southeast of the depression. No doubt, this development has occurred because of the rapidly lessening influence of the persistent upper low. The 6z GFS suggests that this anticyclone will remain collocated with TD3 for at least the next 18 hours, after which point it is forecast to detach from the cyclone and retreat northeastward and gradually open, ultimately becoming absorbed into the western Atlantic subtropical ridge. My current thinking is that the anticyclone will benefit the depression enough to bring it to 45 mph before it approaches southern Florida or the keys. Obviously, the intensity could certainly be higher than this, depending on how well-established, persistent, and strong the anticyclone becomes.
The system, should it go through the Florida Straits, rather than through south Florida, should emerge into the eastern Gulf of Mexico in around 24 hours. Upper-level winds are not forecast to be ideal for intensification, and may only be marginally favorable. However, the shear will primarily be southerly, which would tend to have less of an impact on the cyclone than it ordinarily would. Overall, atmospheric and oceanic conditions conditions appear favorable enough for a 65 mph tropical storm, but this will depend upon the evolution of the upper wind environment across the Gulf.
A large weakness is evident in the subtropical ridge to the north of the cyclone, which is responsible for the current WNW motion. I expect this general motion to continue throughout most of the forecast period, though a more poleward turn could occur by around 60 hours as the system nears the coast of central Louisiana. Just how much of a poleward turn this system takes will depend largely upon the evolution of the aforementioned upper low, which is forecast to continue retreating westward into the Gulf, and eventually move inland by around 54 hours. This is impossible to tell at this point, so residents from Galveston eastward to Biloxi should carefully monitor the progress of this system over the next several days. Another factor regarding the eventual Gulf Coast landfall location of the depression will depend upon a cold front currently moving across the central United States.
My current thinking is that this trough and associated front will at least dent the western extent of the Atlantic subtropical ridge during the next two days. All in all, based upon model analysis as well as other data, I expect the cyclone to ultimately make landfall along the west-central Louisiana coast, just west of Vermilion Bay, though this is obviously not certain. Again, residents across the aforementioned areas should closely monitor the progress of this system over the coming days.
My forecast track agrees well with the NHC's current one, except it's just a little bit to the east.
Invest 98L
Invest 98L continues churning across the Bay of Campeche. Visible satellite animations imply the continued development of deep convection near the center, with some bands of heavy thunderstorms to the north of the circulation. These rains are impacting portions of central Mexico to the south of Tampico, an area just recently battered by Hurricane Alex and Tropical Depression Two. Based on animation of visible satellite imagery and 850 mb vorticity data from CIMSS, I assume that the surface center is located near 20N 95W. An upper-level anticyclone continues to be centered aloft, which favors continued development until the system moves inland. Land interaction is the only inhibiting factor I can see to tropical cyclogenesis, and the system should move inland to the south of Tampico by tonight or early tomorrow morning. The farther south this system goes, the less time it will have over water.
I give this system a 50% chance of becoming a tropical depression prior to moving inland. Were it not for land interaction, I'd go higher. Residents from Veracruz to Tampico should closely monitor the progress of this system. Regardless of development, locally heavy rainfall will overspread the aforementioned areas, and possibly even extreme southern Texas over the next day or two.
Elsewhere
The 12z ECMWF isn't out yet, but the 0z run was still indicating the possibility of our first Cape Verde storm on July 25. The 6z GFS also continues to reflect this possibility. Upper-level winds still appear rather conducive for anything that might happen to form in this area.
Wednesday, July 21, 2010
Tropical weather analysis - July 21, 2010
Invest 97L
Invest 97L continues to struggle with strong vertical wind shear associated with a persistent upper-level low that has branched off from the Tropical Upper Tropospheric Trough (TUTT). The last of the visible satellite images suggest that the exposed low-level center is located at 21N 72W. 97L continues to battle 20 kt of southwesterly shear, associated with the aforementioned upper low. Animation of water vapor imagery and various CIMSS data depicts this upper low rather well from 350 mb upward to around 150 mb. This upper low is keeping all of the convection well to the east of the wave axis, resulting in a highly disorganized system.
However, this upper low has retreated westward over the last six hours, and as a result, shear has decreased over Invest 97L. The GFS continues to persistently indicate that the upper low will continue moving westward away from 97L, being replaced by an upper high, which would reduce the vertical shear over the system and allow for some upper-level ventilation to occur. Water vapor imagery supports the forecast of the GFS, indicating that the upper low has continued to gradually hook westward.
Theoretically, this low should ultimately outrun 97L, leaving a more favorable upper wind environment in place. The 18z GFS indicates that upper-level conditions should begin to significantly improve within about 12 hours. This agrees well with the evolution of the low on water vapor imagery and analysis of upper-air data. This, combined with a large area of dry air to the west, being channeled into the poorly defined low-level center by the upper low, makes it highly unlikely that 97L will significantly intensify tonight, and probably even into the early morning hours on Thursday.
By late morning and into the afternoon, however, the upper flow should vastly improve, as previously noted. Thereafter, upper-level winds appear favorable for some steady development until the system reaches south Florida in around 42-48 hours. Thereafter, the system will emerge into the eastern Gulf of Mexico, where upper-level winds appear to be more conducive than they were this time yesterday, though the aforementioned upper low, as it continues retreating westward, then northwestward and inland, may impart some southerly shear over the system.
I do not expect this shear to be strong enough to be a significant deterrent to development in the Gulf, however.
Given the system's current state of disorganization, it is quite improbable that the system will be able to be any stronger than a minimal tropical storm when it impacts southern Florida. The most likely scenario, however, is a strengthening low pressure system impacting south Florida with gusty winds, rough surf, and heavy rainfall.
Track wise, I expect the system to move generally WNW until around 72 hours, at which point a large weakness in the western Atlantic subtropical ridge is forecast to develop unanimously by nearly all of the computer models. This should bring the system inland somewhere from southeast Louisiana to Destin in about four days.
The CMC continues to suggest that 97L will make landfall along the upper Texas coast, but there is currently no valid reason to assume that this scenario is a reasonable one, since even the CMC keeps a remarkably weak ridge to the east of the system, which wouldn't allow it to move that far west.
None of the models significantly develop 97L, and most actually lose it while it is traversing Florida. The reason for this is unclear, but it could be that the upper low, which will be in the Gulf of Mexico by this time, will pump dry continental air into the circulation, along with natural disruption from passage overland, and finally, southerly shear. This possibility will have to be carefully assessed over the next couple of days, as the models may well be onto something here.
For now, the NHC is giving this system a 40% chance of developing into a tropical cyclone in the next 48 hours, and this is a reasonable forecast.
Invest 98L
The tropical disturbance previously located across the western Caribbean Sea has recently been designated Invest 98L by the National Hurricane Center.
Infrared satellite loops indicate the development of deep convection near the center, which I estimate is at 20N 93W based on animation of infrared RGB imagery.
There is also some weak vorticity noted at 850 mb, though the strongest signature is located inland over the western Yucatan Peninsula, to the east of the deepest convection. Additionally, the overall vorticity is broad and not well organized at the moment. However, upper-level winds are very favorable for development, and an anticyclone aloft is noted based on CIMSS wind shear data. The GFS keeps this anticyclone intact until 54 hours, at which point the system should be inland. Ergo, I believe it is quite possible that we will see a tropical cyclone out of this area prior to it moving inland near Tampico, Mexico. The farther south it goes, however, the less time it will have over water. This situation looks similar to 2005's Tropical Storm Bret, and also to Hurricane Alex earlier this year.
Indeed, this area might have a greater chance to develop than 97L does. The primary inhibiting factor will be land interaction.
Elsewhere
Elsewhere in the tropics, the reliable ECMWF continues to indicate the development of our first Cape Verde system, or at least a strong low pressure area, near the northern Cape Verde Islands on July 25. This model, along with the GFS, has been hinting at the possibility of tropical cyclogenesis in this area for awhile.
This appears to be a reasonable forecast, and upper-level winds favor development of anything that does happen to form here.
Invest 97L continues to struggle with strong vertical wind shear associated with a persistent upper-level low that has branched off from the Tropical Upper Tropospheric Trough (TUTT). The last of the visible satellite images suggest that the exposed low-level center is located at 21N 72W. 97L continues to battle 20 kt of southwesterly shear, associated with the aforementioned upper low. Animation of water vapor imagery and various CIMSS data depicts this upper low rather well from 350 mb upward to around 150 mb. This upper low is keeping all of the convection well to the east of the wave axis, resulting in a highly disorganized system.
However, this upper low has retreated westward over the last six hours, and as a result, shear has decreased over Invest 97L. The GFS continues to persistently indicate that the upper low will continue moving westward away from 97L, being replaced by an upper high, which would reduce the vertical shear over the system and allow for some upper-level ventilation to occur. Water vapor imagery supports the forecast of the GFS, indicating that the upper low has continued to gradually hook westward.
Theoretically, this low should ultimately outrun 97L, leaving a more favorable upper wind environment in place. The 18z GFS indicates that upper-level conditions should begin to significantly improve within about 12 hours. This agrees well with the evolution of the low on water vapor imagery and analysis of upper-air data. This, combined with a large area of dry air to the west, being channeled into the poorly defined low-level center by the upper low, makes it highly unlikely that 97L will significantly intensify tonight, and probably even into the early morning hours on Thursday.
By late morning and into the afternoon, however, the upper flow should vastly improve, as previously noted. Thereafter, upper-level winds appear favorable for some steady development until the system reaches south Florida in around 42-48 hours. Thereafter, the system will emerge into the eastern Gulf of Mexico, where upper-level winds appear to be more conducive than they were this time yesterday, though the aforementioned upper low, as it continues retreating westward, then northwestward and inland, may impart some southerly shear over the system.
I do not expect this shear to be strong enough to be a significant deterrent to development in the Gulf, however.
Given the system's current state of disorganization, it is quite improbable that the system will be able to be any stronger than a minimal tropical storm when it impacts southern Florida. The most likely scenario, however, is a strengthening low pressure system impacting south Florida with gusty winds, rough surf, and heavy rainfall.
Track wise, I expect the system to move generally WNW until around 72 hours, at which point a large weakness in the western Atlantic subtropical ridge is forecast to develop unanimously by nearly all of the computer models. This should bring the system inland somewhere from southeast Louisiana to Destin in about four days.
The CMC continues to suggest that 97L will make landfall along the upper Texas coast, but there is currently no valid reason to assume that this scenario is a reasonable one, since even the CMC keeps a remarkably weak ridge to the east of the system, which wouldn't allow it to move that far west.
None of the models significantly develop 97L, and most actually lose it while it is traversing Florida. The reason for this is unclear, but it could be that the upper low, which will be in the Gulf of Mexico by this time, will pump dry continental air into the circulation, along with natural disruption from passage overland, and finally, southerly shear. This possibility will have to be carefully assessed over the next couple of days, as the models may well be onto something here.
For now, the NHC is giving this system a 40% chance of developing into a tropical cyclone in the next 48 hours, and this is a reasonable forecast.
Invest 98L
The tropical disturbance previously located across the western Caribbean Sea has recently been designated Invest 98L by the National Hurricane Center.
Infrared satellite loops indicate the development of deep convection near the center, which I estimate is at 20N 93W based on animation of infrared RGB imagery.
There is also some weak vorticity noted at 850 mb, though the strongest signature is located inland over the western Yucatan Peninsula, to the east of the deepest convection. Additionally, the overall vorticity is broad and not well organized at the moment. However, upper-level winds are very favorable for development, and an anticyclone aloft is noted based on CIMSS wind shear data. The GFS keeps this anticyclone intact until 54 hours, at which point the system should be inland. Ergo, I believe it is quite possible that we will see a tropical cyclone out of this area prior to it moving inland near Tampico, Mexico. The farther south it goes, however, the less time it will have over water. This situation looks similar to 2005's Tropical Storm Bret, and also to Hurricane Alex earlier this year.
Indeed, this area might have a greater chance to develop than 97L does. The primary inhibiting factor will be land interaction.
Elsewhere
Elsewhere in the tropics, the reliable ECMWF continues to indicate the development of our first Cape Verde system, or at least a strong low pressure area, near the northern Cape Verde Islands on July 25. This model, along with the GFS, has been hinting at the possibility of tropical cyclogenesis in this area for awhile.
This appears to be a reasonable forecast, and upper-level winds favor development of anything that does happen to form here.
Tuesday, July 20, 2010
Tropical weather analysis - July 20, 2010
Invest 97L
Invest 97L has become better organized today, with infrared satellite animations depicting deep convection developing and persisting near the estimated surface center (don't confuse this with a surface low, as there isn't one just yet), which, based on animation of shortwave infrared satellite imagery is located near 19N 68W. Surface observations from Puerto Rico show no evidence of a closed surface circulation in associated with the system, with no reports of westerly winds along the southern flank of the circulation. In addition, analysis of observations from the National Data Buoy Center indicate that, other than some slight pressure falls noted across Puerto Rico this afternoon, surrounding pressures really aren't all that low.
This is another strong indication that 97L has not yet developed a surface low pressure area. Until this happens, and the center subsequently closes off, tropical cyclogenesis cannot occur.
97L is still experiencing strong vertical shear, in excess of 15 to 20 kt, due to a large upper-level low centered a couple hundred miles north of the disturbance. The current motion of 97L is very difficult to ascertain, due to deep convection obscuring the center, along with the overall lack of a well-defined surface center. My best estimate is very slowly to the WNW. The aforementioned upper low responsible for the shear, centered near 25N 70W, was revealed rather well from 350 to 150 mb. Analysis of the 18z GFS 300 mb vorticity suggests that this upper low will continue moving generally westward away from 97L, which should allow 97L to begin to consolidate more thoroughly by tomorrow.
Thereafter, the GFS develops a weak anticyclone aloft over the system, which would favor intensification. I am not expecting 97L to become a tropical depression until tomorrow afternoon at the earliest, with the most likely time being Thursday morning.
My forecast track has been shifted northward from yesterday. I expect that 97L will continue moving WNW over the next three to four days, making landfall across south Florida in around 60-72 hours. Late on day three, the system should emerge from Florida into the eastern Gulf of Mexico. Upper-level winds don't appear as favorable there as they will be in the western Atlantic, but are still more than adequate to support some steady intensification of the system until landfall occurs.
The ultimate landfall location of 97L along the Gulf Coast will depend upon the strength and orientation of the westward extension of the subtropical ridge. Some models keep this weaker, which would place the northeastern Gulf Coast at higher risk, while some keep it stronger, which would put the northern Gulf Coast in the bullseye.
An alternate scenario, as depicted by the 12z CMC, is for the system to run into Hispaniola in the next 12 hours, before bending back toward the WNW. Current 850 mb steering analysis from CIMSS somewhat supports this, but the ridge to the north has also been weakening in recent hours, so I am not expecting 97L to traverse Hispaniola.
Residents all along the Florida peninsula, as well as the Gulf Coast, particularly from Morgan City to Tallahassee, should carefully monitor the progress of this system over the next several days. Regardless of development, locally heavy rainfall and gusty winds in excess of tropical storm force will continue impacting portions of Puerto Rico, the Virgin Islands, and Hispaniola over the next couple of days. These rains could cause flash flooding and mudslides across mountainous regions of these countries.
Elsewhere
An area of disturbed weather, associated with a tropical wave, continues in the western Caribbean Sea. The system is very poorly-defined, with very little evidence of low- to mid-level vorticity. Upper-level winds are expected to become unfavorable for development as the system moves generally westward. While I am not expecting development from this area, it could produce locally heavy rainfall across portions of the Cayman Islands and the Yucatan Peninsula over the next day or so.
The ECMWF and GFS continue to suggest the possibility of our first Cape Verde storm developing on July 25. Given the abundant moisture currently across eastern Africa (as well as the entire African continent), this is a believable forecast. Upper-level winds will be favorable for anything that does happen to form here. These models have been indicating this possibility for over a day now, so it certainly bears watching.
Invest 97L has become better organized today, with infrared satellite animations depicting deep convection developing and persisting near the estimated surface center (don't confuse this with a surface low, as there isn't one just yet), which, based on animation of shortwave infrared satellite imagery is located near 19N 68W. Surface observations from Puerto Rico show no evidence of a closed surface circulation in associated with the system, with no reports of westerly winds along the southern flank of the circulation. In addition, analysis of observations from the National Data Buoy Center indicate that, other than some slight pressure falls noted across Puerto Rico this afternoon, surrounding pressures really aren't all that low.
This is another strong indication that 97L has not yet developed a surface low pressure area. Until this happens, and the center subsequently closes off, tropical cyclogenesis cannot occur.
97L is still experiencing strong vertical shear, in excess of 15 to 20 kt, due to a large upper-level low centered a couple hundred miles north of the disturbance. The current motion of 97L is very difficult to ascertain, due to deep convection obscuring the center, along with the overall lack of a well-defined surface center. My best estimate is very slowly to the WNW. The aforementioned upper low responsible for the shear, centered near 25N 70W, was revealed rather well from 350 to 150 mb. Analysis of the 18z GFS 300 mb vorticity suggests that this upper low will continue moving generally westward away from 97L, which should allow 97L to begin to consolidate more thoroughly by tomorrow.
Thereafter, the GFS develops a weak anticyclone aloft over the system, which would favor intensification. I am not expecting 97L to become a tropical depression until tomorrow afternoon at the earliest, with the most likely time being Thursday morning.
My forecast track has been shifted northward from yesterday. I expect that 97L will continue moving WNW over the next three to four days, making landfall across south Florida in around 60-72 hours. Late on day three, the system should emerge from Florida into the eastern Gulf of Mexico. Upper-level winds don't appear as favorable there as they will be in the western Atlantic, but are still more than adequate to support some steady intensification of the system until landfall occurs.
The ultimate landfall location of 97L along the Gulf Coast will depend upon the strength and orientation of the westward extension of the subtropical ridge. Some models keep this weaker, which would place the northeastern Gulf Coast at higher risk, while some keep it stronger, which would put the northern Gulf Coast in the bullseye.
An alternate scenario, as depicted by the 12z CMC, is for the system to run into Hispaniola in the next 12 hours, before bending back toward the WNW. Current 850 mb steering analysis from CIMSS somewhat supports this, but the ridge to the north has also been weakening in recent hours, so I am not expecting 97L to traverse Hispaniola.
Residents all along the Florida peninsula, as well as the Gulf Coast, particularly from Morgan City to Tallahassee, should carefully monitor the progress of this system over the next several days. Regardless of development, locally heavy rainfall and gusty winds in excess of tropical storm force will continue impacting portions of Puerto Rico, the Virgin Islands, and Hispaniola over the next couple of days. These rains could cause flash flooding and mudslides across mountainous regions of these countries.
Elsewhere
An area of disturbed weather, associated with a tropical wave, continues in the western Caribbean Sea. The system is very poorly-defined, with very little evidence of low- to mid-level vorticity. Upper-level winds are expected to become unfavorable for development as the system moves generally westward. While I am not expecting development from this area, it could produce locally heavy rainfall across portions of the Cayman Islands and the Yucatan Peninsula over the next day or so.
The ECMWF and GFS continue to suggest the possibility of our first Cape Verde storm developing on July 25. Given the abundant moisture currently across eastern Africa (as well as the entire African continent), this is a believable forecast. Upper-level winds will be favorable for anything that does happen to form here. These models have been indicating this possibility for over a day now, so it certainly bears watching.
Monday, July 19, 2010
Tropical weather analysis - July 19, 2010
Invest 97L
A strong tropical wave located just to the north of Puerto Rico was designated Invest 97L by the National Hurricane Center early this morning. This wave is generating a significant amount of deep convection this evening. However, 97L is also experiencing 20 kt of westerly vertical shear, associated with a large and persistent upper-level low, the axis of which is centered near 28N 68N, based on animation of water vapor imagery. As far as the center estimate for 97L goes, it is pretty difficult to locate, but my best estimate is 19N 65W. Surface pressures are not significantly falling, and there are no signs of a surface circulation.
Overall, despite the fact that convection has been persisting near the estimated center position this evening, the aforementioned factors should limit any development over the next day or so, and I expect that this current convective burst will soon be sheared off to the east due to strong upper-level winds. In the meantime, locally heavy rainfall and strong gusty winds will continue overspreading portions of the Leeward Islands, Puerto Rico, the Virgin Islands, and Hispaniola over the next day or so.
97L appears to be moving toward the W at the moment. However, this should be short-lived, as a weakness in the low-levels is becoming apparent in the subtropical ridge to the north. This weakness is even more pronounced at 500 mb. This should begin to impart a WNW component of motion within the next 6-12 hours. I find it unlikely that 97L will run into the Greater Antilles, at least in the near-term. However, by around 60 hours or so, it could be approaching eastern Cuba. This is the solution unanimously provided by the computer models, and is what I'll go with for the time being. This will really depend on how quickly the aforementioned upper low fades, and the subsequent rebuilding of the ridge.
A weaker ridge may allow it to avoid Cuba entirely, while a stronger one would take it farther south, across eastern Cuba. I'll continue monitoring the evolution of the upper low/ridge over the next couple of days. It should be noted that as the system approaches Cuba or the Bahamas on day two or three, upper-level shear will still be strong, but falling.
In any case, after moving across Cuba, the system should emerge into the eastern Gulf of Mexico sometime on day four. After that, the models foresee a large weakness developing in the subtropical ridge, which would tend to impart a poleward component of motion after the system enters the Gulf. However, I would like to see some more consistency with regards to this before I jump on the poleward bandwagon, since not only has the anomalously strong ridging across the Gulf of Mexico been difficult to break or bend this year (ala, Alex and Tropical Depression Two), the GFS was foreseeing a stronger ridge at 12z than it was at 18z.
Residents all along the Gulf Coast should closely monitor the progress of this system over the next several days. I do think that this system has a decent chance of ultimately becoming a tropical cyclone, though this might not happen until after it enters the Gulf. I want residents to be aware of this situation, as the GFS continues to build an anticyclone across the Gulf at four days and beyond, which would greatly favor intensification or development.
A reconnaissance aircraft is scheduled to investigate this system tomorrow, if necessary.
Caribbean disturbance
Another tropical wave, this one located across the western Caribbean Sea, is generating a large area of disorganized showers and thunderstorms across the western Caribbean Sea. Upper-level winds are forecast to remain favorable for development as this system moves generally westward. In fact, CIMSS analysis indicates that an upper-level anticyclone may be forming, and the 18z GFS builds this anticyclone over the next several days. Though the NHC has officially ceased mentioning the disturbance in their Tropical Weather Outlook, I will continue to monitor it, as conditions appear rather favorable for development over the next several days. The biggest inhibiting factor I can see is land interaction; this system will run into Central America, Belize, or the Yucatan Peninsula in about three days. Hence, if it's going to develop, it has to do so quickly.
Regardless of development, locally heavy rainfall will continue affecting portions of Jamaica, the Cayman Islands, and western Cuba over the next couple of days.
A strong tropical wave located just to the north of Puerto Rico was designated Invest 97L by the National Hurricane Center early this morning. This wave is generating a significant amount of deep convection this evening. However, 97L is also experiencing 20 kt of westerly vertical shear, associated with a large and persistent upper-level low, the axis of which is centered near 28N 68N, based on animation of water vapor imagery. As far as the center estimate for 97L goes, it is pretty difficult to locate, but my best estimate is 19N 65W. Surface pressures are not significantly falling, and there are no signs of a surface circulation.
Overall, despite the fact that convection has been persisting near the estimated center position this evening, the aforementioned factors should limit any development over the next day or so, and I expect that this current convective burst will soon be sheared off to the east due to strong upper-level winds. In the meantime, locally heavy rainfall and strong gusty winds will continue overspreading portions of the Leeward Islands, Puerto Rico, the Virgin Islands, and Hispaniola over the next day or so.
97L appears to be moving toward the W at the moment. However, this should be short-lived, as a weakness in the low-levels is becoming apparent in the subtropical ridge to the north. This weakness is even more pronounced at 500 mb. This should begin to impart a WNW component of motion within the next 6-12 hours. I find it unlikely that 97L will run into the Greater Antilles, at least in the near-term. However, by around 60 hours or so, it could be approaching eastern Cuba. This is the solution unanimously provided by the computer models, and is what I'll go with for the time being. This will really depend on how quickly the aforementioned upper low fades, and the subsequent rebuilding of the ridge.
A weaker ridge may allow it to avoid Cuba entirely, while a stronger one would take it farther south, across eastern Cuba. I'll continue monitoring the evolution of the upper low/ridge over the next couple of days. It should be noted that as the system approaches Cuba or the Bahamas on day two or three, upper-level shear will still be strong, but falling.
In any case, after moving across Cuba, the system should emerge into the eastern Gulf of Mexico sometime on day four. After that, the models foresee a large weakness developing in the subtropical ridge, which would tend to impart a poleward component of motion after the system enters the Gulf. However, I would like to see some more consistency with regards to this before I jump on the poleward bandwagon, since not only has the anomalously strong ridging across the Gulf of Mexico been difficult to break or bend this year (ala, Alex and Tropical Depression Two), the GFS was foreseeing a stronger ridge at 12z than it was at 18z.
Residents all along the Gulf Coast should closely monitor the progress of this system over the next several days. I do think that this system has a decent chance of ultimately becoming a tropical cyclone, though this might not happen until after it enters the Gulf. I want residents to be aware of this situation, as the GFS continues to build an anticyclone across the Gulf at four days and beyond, which would greatly favor intensification or development.
A reconnaissance aircraft is scheduled to investigate this system tomorrow, if necessary.
Caribbean disturbance
Another tropical wave, this one located across the western Caribbean Sea, is generating a large area of disorganized showers and thunderstorms across the western Caribbean Sea. Upper-level winds are forecast to remain favorable for development as this system moves generally westward. In fact, CIMSS analysis indicates that an upper-level anticyclone may be forming, and the 18z GFS builds this anticyclone over the next several days. Though the NHC has officially ceased mentioning the disturbance in their Tropical Weather Outlook, I will continue to monitor it, as conditions appear rather favorable for development over the next several days. The biggest inhibiting factor I can see is land interaction; this system will run into Central America, Belize, or the Yucatan Peninsula in about three days. Hence, if it's going to develop, it has to do so quickly.
Regardless of development, locally heavy rainfall will continue affecting portions of Jamaica, the Cayman Islands, and western Cuba over the next couple of days.
Wednesday, July 7, 2010
Tropical weather analysis - July 7, 2010
Invest 96L has become significantly better organized this evening, with visible satellite animations depicting a well-organized system, with deep convection increasing near the center of circulation, which I estimate is located at 24N 93W. However, this isn't completely certain, because the center is clearly tucked underneath the deep convection, and isn't even partially exposed.
In addition, surface pressures appear to be low and falling within several hundred miles of the disturbance, and surface and buoy observations suggest that this system has a well-defined surface circulation. Station 42002, located in the western Gulf of Mexico at 25N 93W, isn't even in the deepest convection associated with 96L, and is already reporting sustained winds of around 22 mph, with gusts to around 28 mph. This suggests that sustained surface winds are likely near 30 mph within the deepest convection near the center. However, I should note that cloud top temperatures aren't particularly cold near the estimated center, only around -60C. This is likely due to passage of cooler water upwelled by Hurricane Alex. As 96L pulls away from this cold wake, however, it should be able to generate colder convection and subsequently intensify.
This system appears to have an upper-level anticyclone centered directly atop the estimated surface center. Obviously, this will guard it from any vertical shear. The 18z GFS keeps an anticyclonic environment within the vicinity of 96L over the next 24 hours. This should allow for continued intensification of the system, particularly after it pulls away from Alex's cold wake. All in all, a tropical depression appears to be imminent from this system. I am expecting this system to attain tropical storm status, peaking at 50 mph. Interests from northeastern Mexico to central Texas should carefully monitor the progress of this system over the next day or so. Regardless of development, locally heavy rainfall and gusty winds will begin to overspread portions of northeastern Mexico and southern Texas tonight and into tomorrow.
The track for this system is very straightforward. The current NW motion should continue for the next 6-12 hours, after which point a building ridge to the north should begin to impart a more WNW component of motion. This system should be inland in less than 24 hours, I'd say about 18-20 hours. I have the landfall location between Brownsville and Port Mansfield.
In addition, surface pressures appear to be low and falling within several hundred miles of the disturbance, and surface and buoy observations suggest that this system has a well-defined surface circulation. Station 42002, located in the western Gulf of Mexico at 25N 93W, isn't even in the deepest convection associated with 96L, and is already reporting sustained winds of around 22 mph, with gusts to around 28 mph. This suggests that sustained surface winds are likely near 30 mph within the deepest convection near the center. However, I should note that cloud top temperatures aren't particularly cold near the estimated center, only around -60C. This is likely due to passage of cooler water upwelled by Hurricane Alex. As 96L pulls away from this cold wake, however, it should be able to generate colder convection and subsequently intensify.
This system appears to have an upper-level anticyclone centered directly atop the estimated surface center. Obviously, this will guard it from any vertical shear. The 18z GFS keeps an anticyclonic environment within the vicinity of 96L over the next 24 hours. This should allow for continued intensification of the system, particularly after it pulls away from Alex's cold wake. All in all, a tropical depression appears to be imminent from this system. I am expecting this system to attain tropical storm status, peaking at 50 mph. Interests from northeastern Mexico to central Texas should carefully monitor the progress of this system over the next day or so. Regardless of development, locally heavy rainfall and gusty winds will begin to overspread portions of northeastern Mexico and southern Texas tonight and into tomorrow.
The track for this system is very straightforward. The current NW motion should continue for the next 6-12 hours, after which point a building ridge to the north should begin to impart a more WNW component of motion. This system should be inland in less than 24 hours, I'd say about 18-20 hours. I have the landfall location between Brownsville and Port Mansfield.
Tuesday, July 6, 2010
Tropical weather analysis - July 6, 2010
Invest 96L
Invest 96L continues to be persistent. As of this evening, it appears to be located across the northern Yucatan Peninsula about 60 miles east of Merida. This is based on shortwave infrared satellite animations as well as recent surface observations. The estimated center position, based on the above, is 20N 89W. Convection is currently minimal near the estimated center position, though this is undoubtedly because it is currently overland. What's interesting to me, however, is that satellite loops finally indicate the development of upper-level outflow.
This recent development and expansion of upper-level outflow is no doubt associated with a well-defined upper-level anticyclone that, while not directly atop the center, is at least close enough to ventilate the system, rather than shear it. The system appears to be moving WNW at the moment. This motion could continue for the next 6-12 hours, but after that, I expect a turn back to the NW. That should continue until after 48 hours, at which point the ridge could rebuild to the north and force a more WNW component of motion. The models have shifted considerably southward today, and thus I am forced to do the same. Unfortunately, this puts south Texas and northeast Mexico back in the bullseye, after having just dealt with Hurricane Alex, which generated considerable flooding that is still ongoing.
The models still appear to be too quick in bringing this system into the USA (or Mexico), generally bringing it inland in about 48 hours. I will forecast a landfall in the USA/Mexico in about 60 hours. This is based on CIMSS steering analysis, which does not appear to be as quick as the models are saying. This system should emerge into the southern Gulf of Mexico sometime tomorrow morning.
Upper-level winds still appear to be marginally conducive for some development of this system over the next couple of days, but the overall environment across the Gulf of Mexico will certainly not be anticyclonic. The NHC is giving this system a 40% chance of becoming a tropical cyclone within the next 48 hours. This is a reasonable forecast. I still think that this has a decent chance of becoming the season's second named storm, though at this point it no longer appears as if it will become a hurricane, because of the southward shift in the models today. It will instead pass over Alex's cold wake, generated south of 25N, which will tend to inhibit any rapid intensification. Hence, I expect only gradual intensification, assuming the system forms at all.
I forecast a landfall somewhere across south Texas in 60 hours, though it is difficult to pinpoint the exact location within that vicinity. Interests from northeast Mexico to southeast Texas should continue to carefully monitor the progress of this system over the next couple of days. In the meantime, locally heavy rainfall will continue overspreading portions of the Yucatan Peninsula, western Cuba, and the Cayman Islands over the next day or so.
Eastern Caribbean tropical wave
A tropical wave moving westward across the eastern Caribbean Sea is very disorganized, and upper-level winds are forecast to remain unfavorable for tropical cyclogenesis as the wave moves W to WNW at 15 to 20 kt over the next several days. This will be my final mention of this system unless some drastic changes are noted.
Bahamas/western Atlantic system
A disorganized area of showers and thunderstorms located from the Bahamas eastward for several hundred miles is associated with the remnants of an old cold front (now a trough). Upper-level winds are forecast to become more conducive for development as the system moves little over the next couple of days. Eventually, the system could move NE. The GFS continues to hint at development of this feature.
Invest 96L continues to be persistent. As of this evening, it appears to be located across the northern Yucatan Peninsula about 60 miles east of Merida. This is based on shortwave infrared satellite animations as well as recent surface observations. The estimated center position, based on the above, is 20N 89W. Convection is currently minimal near the estimated center position, though this is undoubtedly because it is currently overland. What's interesting to me, however, is that satellite loops finally indicate the development of upper-level outflow.
This recent development and expansion of upper-level outflow is no doubt associated with a well-defined upper-level anticyclone that, while not directly atop the center, is at least close enough to ventilate the system, rather than shear it. The system appears to be moving WNW at the moment. This motion could continue for the next 6-12 hours, but after that, I expect a turn back to the NW. That should continue until after 48 hours, at which point the ridge could rebuild to the north and force a more WNW component of motion. The models have shifted considerably southward today, and thus I am forced to do the same. Unfortunately, this puts south Texas and northeast Mexico back in the bullseye, after having just dealt with Hurricane Alex, which generated considerable flooding that is still ongoing.
The models still appear to be too quick in bringing this system into the USA (or Mexico), generally bringing it inland in about 48 hours. I will forecast a landfall in the USA/Mexico in about 60 hours. This is based on CIMSS steering analysis, which does not appear to be as quick as the models are saying. This system should emerge into the southern Gulf of Mexico sometime tomorrow morning.
Upper-level winds still appear to be marginally conducive for some development of this system over the next couple of days, but the overall environment across the Gulf of Mexico will certainly not be anticyclonic. The NHC is giving this system a 40% chance of becoming a tropical cyclone within the next 48 hours. This is a reasonable forecast. I still think that this has a decent chance of becoming the season's second named storm, though at this point it no longer appears as if it will become a hurricane, because of the southward shift in the models today. It will instead pass over Alex's cold wake, generated south of 25N, which will tend to inhibit any rapid intensification. Hence, I expect only gradual intensification, assuming the system forms at all.
I forecast a landfall somewhere across south Texas in 60 hours, though it is difficult to pinpoint the exact location within that vicinity. Interests from northeast Mexico to southeast Texas should continue to carefully monitor the progress of this system over the next couple of days. In the meantime, locally heavy rainfall will continue overspreading portions of the Yucatan Peninsula, western Cuba, and the Cayman Islands over the next day or so.
Eastern Caribbean tropical wave
A tropical wave moving westward across the eastern Caribbean Sea is very disorganized, and upper-level winds are forecast to remain unfavorable for tropical cyclogenesis as the wave moves W to WNW at 15 to 20 kt over the next several days. This will be my final mention of this system unless some drastic changes are noted.
Bahamas/western Atlantic system
A disorganized area of showers and thunderstorms located from the Bahamas eastward for several hundred miles is associated with the remnants of an old cold front (now a trough). Upper-level winds are forecast to become more conducive for development as the system moves little over the next couple of days. Eventually, the system could move NE. The GFS continues to hint at development of this feature.
Monday, July 5, 2010
Tropical weather analysis - July 5, 2010
Invest 95L
Invest 95L has recently moved inland between Morgan City and Houma, Louisiana. This is suggested by shortwave infrared satellite animations, along with doppler radar animations from Slidell, Louisiana. 95L appeared to be on the verge of becoming a tropical depression in the several hours prior to landfall, with both doppler radar and satellite animations suggesting increased organization, including the formation of low-level spiral banding.
Based on radar and satellite data, I assume that the surface center is located at 29N 91W, and moving slowly to the NW. This general motion should continue for at least the next 12-18 hours. Thereafter, the system should turn N and NE ahead of a mid-latitude trough in the westerlies. The main threat from this system is heavy rainfall, which could be in excess of 1 to 3 inches per hour right near the center. In the last 24 hours, as much as 6 inches of rain has fallen about 75 miles south of Houma right near the core of the storm.
The other impact from 95L will be sustained winds in excess of 25 to 30 mph right near the center, with gusts up to tropical storm force. These winds could blow around unsecured objects, as well as down small trees. Heavy rains in excess of 1 to 3 inches, with locally higher amounts could overspread portions of central and southeastern Louisiana over the next 12-18 hours. These rains could produce some localized flooding in some areas.
This will be my final mention of Invest 95L.
Invest 96L
Invest 96L, located across the extreme western Caribbean Sea, continues to be a far greater threat than any other area in the Atlantic, at least immediately speaking (there are other areas of interest, which I'll get to in a bit), and all in all, I feel this has a good chance of developing into the season's second named storm.
The center isn't especially easy to locate, but based on animation of shortwave infrared satellite imagery, I put it near 20N 86W. Surface pressures, while somewhat low, are not overly so, and have actually been somewhat rising over the last several hours (though some areas have seen nearly steady-state surface pressures). Surface and buoy observations are not currently suggesting anything resembling a closed surface circulation. Unfortunately, ASCAT completely missed the disturbance, as is usually the case, so we cannot ascertain just how much of a surface signature is associated with this feature, if there is any at all. CIMSS analysis depicts 20 kt of northwesterly shear impinging upon the estimated center of the system.
This shear is associated with a small but well-defined upper-level anticyclone currently centered across the northeastern portion of the Yucatan Peninsula. 96L appears to be moving NW at 10 to 15 kt, under the influence of a weak low- and mid-level ridge. The system is not presently stacked in the vertical, with a noticeable southeastward tilt of the 850 mb and 700 mb vorticity centers.
I am not expecting any significant development of 96L for at least the next day or so. It should enter the southern Gulf of Mexico within the next several hours. The 18z GFS does not call for a significantly anticyclonic environment across the Gulf of Mexico as it did at this time yesterday. In fact, the upper wind environment might well be a zonal one until after 24 hours. So, although upper-level winds do appear conducive enough for at least some slow development, it is not looking as favorable as it was this time yesterday. However, SSTs are plenty warm, and the warm water extends to a moderate depth.
There is a heat eddy in the south-central Gulf of Mexico from 24N-25N and 87W-88W. Should 96L pass over this heat eddy (which is possible, particularly the extreme western edge of the eddy), it could find enough heat energy to rapidly transition to a tropical cyclone. There is also a noticeable, much larger swath of heat from 96W to 91W and from 25N to 28N. This will also provide the system with additional heat energy. All in all, I expect this system to become a tropical depression within the next 48 hours, though it could occur somewhat sooner if the system becomes significantly better organized during the day tomorrow. Regardless of development, locally heavy rainfall will overspread portions of the Yucatan Peninsula, western Cuba, and the Cayman Islands over the 12 hours or so, and then the Florida Keys after that.
The majority of the models take the system into southeastern Texas in about 48-54 hours, though none of them are showing the system as being particularly strong. This may be an indication (more like a compliment, actually) that the upper-level environment will not be as favorable as previously thought. However, I don't see anything within the upper-level environment to keep this system as weak as most of the models are forecasting. Only the SHIPS significantly intensifies the system, bringing it to just under hurricane status in 72 hours. The other models, save the ECMWF, are much quicker in bringing the system inland, so the SHIPS does look suspect. The reliable ECMWF is also a late landfall model, forecasting the system to be inland by 72 hours, rather than at 48-54 hours as the general consensus predicts.
However, the ECMWF also looks suspect, because it's much too far south, bringing the system inland near Port Mansfield. I have opted to discount this scenario for now, and instead forecast a southeast Texas landfall at around 60 hours. The biggest reason this system may not be as powerful as previously thought is that it has very little time to get its act together before it moves inland. Nevertheless, residents across the western Caribbean and the Gulf of Mexico should carefully monitor the progress of this system over the next couple of days. I expect that this system will become a moderate tropical storm, and possibly a minimal hurricane.
Eastern Caribbean tropical wave
A tropical wave located in the eastern Caribbean Sea is interacting with an upper-level trough and generating a large area of cloudiness and showers across the eastern Caribbean and adjacent Windward Islands. Upper-level winds are currently unfavorable for development, but are forecast to become more conducive as the system moves to the WNW at around 15 kt over the next several days. None of the computer models are currently developing this wave, but it bears watching, given that the upper environment could improve over the next couple days (though the general flow looks to remain largely zonal at this point).
Bahamas disturbance
Another disturbance is located over the Bahamas, and is associated with a cold front. Upper-level winds are not currently favorable for development, though they are forecast to improve gradually over the next several days as the system moves little. All in all though, this area is rather unimpressive at the moment, and I suspect that any development will be very slow to occur. The CMC and GFS (operational) are hinting at development of this system in about four days, though they show it, fortunately, recurving out to sea ahead of an upper-level trough. The NOGAPS keeps the ridge stronger, however, which would force the system on a W track into the Gulf of Mexico.
Invest 95L has recently moved inland between Morgan City and Houma, Louisiana. This is suggested by shortwave infrared satellite animations, along with doppler radar animations from Slidell, Louisiana. 95L appeared to be on the verge of becoming a tropical depression in the several hours prior to landfall, with both doppler radar and satellite animations suggesting increased organization, including the formation of low-level spiral banding.
Based on radar and satellite data, I assume that the surface center is located at 29N 91W, and moving slowly to the NW. This general motion should continue for at least the next 12-18 hours. Thereafter, the system should turn N and NE ahead of a mid-latitude trough in the westerlies. The main threat from this system is heavy rainfall, which could be in excess of 1 to 3 inches per hour right near the center. In the last 24 hours, as much as 6 inches of rain has fallen about 75 miles south of Houma right near the core of the storm.
The other impact from 95L will be sustained winds in excess of 25 to 30 mph right near the center, with gusts up to tropical storm force. These winds could blow around unsecured objects, as well as down small trees. Heavy rains in excess of 1 to 3 inches, with locally higher amounts could overspread portions of central and southeastern Louisiana over the next 12-18 hours. These rains could produce some localized flooding in some areas.
This will be my final mention of Invest 95L.
Invest 96L
Invest 96L, located across the extreme western Caribbean Sea, continues to be a far greater threat than any other area in the Atlantic, at least immediately speaking (there are other areas of interest, which I'll get to in a bit), and all in all, I feel this has a good chance of developing into the season's second named storm.
The center isn't especially easy to locate, but based on animation of shortwave infrared satellite imagery, I put it near 20N 86W. Surface pressures, while somewhat low, are not overly so, and have actually been somewhat rising over the last several hours (though some areas have seen nearly steady-state surface pressures). Surface and buoy observations are not currently suggesting anything resembling a closed surface circulation. Unfortunately, ASCAT completely missed the disturbance, as is usually the case, so we cannot ascertain just how much of a surface signature is associated with this feature, if there is any at all. CIMSS analysis depicts 20 kt of northwesterly shear impinging upon the estimated center of the system.
This shear is associated with a small but well-defined upper-level anticyclone currently centered across the northeastern portion of the Yucatan Peninsula. 96L appears to be moving NW at 10 to 15 kt, under the influence of a weak low- and mid-level ridge. The system is not presently stacked in the vertical, with a noticeable southeastward tilt of the 850 mb and 700 mb vorticity centers.
I am not expecting any significant development of 96L for at least the next day or so. It should enter the southern Gulf of Mexico within the next several hours. The 18z GFS does not call for a significantly anticyclonic environment across the Gulf of Mexico as it did at this time yesterday. In fact, the upper wind environment might well be a zonal one until after 24 hours. So, although upper-level winds do appear conducive enough for at least some slow development, it is not looking as favorable as it was this time yesterday. However, SSTs are plenty warm, and the warm water extends to a moderate depth.
There is a heat eddy in the south-central Gulf of Mexico from 24N-25N and 87W-88W. Should 96L pass over this heat eddy (which is possible, particularly the extreme western edge of the eddy), it could find enough heat energy to rapidly transition to a tropical cyclone. There is also a noticeable, much larger swath of heat from 96W to 91W and from 25N to 28N. This will also provide the system with additional heat energy. All in all, I expect this system to become a tropical depression within the next 48 hours, though it could occur somewhat sooner if the system becomes significantly better organized during the day tomorrow. Regardless of development, locally heavy rainfall will overspread portions of the Yucatan Peninsula, western Cuba, and the Cayman Islands over the 12 hours or so, and then the Florida Keys after that.
The majority of the models take the system into southeastern Texas in about 48-54 hours, though none of them are showing the system as being particularly strong. This may be an indication (more like a compliment, actually) that the upper-level environment will not be as favorable as previously thought. However, I don't see anything within the upper-level environment to keep this system as weak as most of the models are forecasting. Only the SHIPS significantly intensifies the system, bringing it to just under hurricane status in 72 hours. The other models, save the ECMWF, are much quicker in bringing the system inland, so the SHIPS does look suspect. The reliable ECMWF is also a late landfall model, forecasting the system to be inland by 72 hours, rather than at 48-54 hours as the general consensus predicts.
However, the ECMWF also looks suspect, because it's much too far south, bringing the system inland near Port Mansfield. I have opted to discount this scenario for now, and instead forecast a southeast Texas landfall at around 60 hours. The biggest reason this system may not be as powerful as previously thought is that it has very little time to get its act together before it moves inland. Nevertheless, residents across the western Caribbean and the Gulf of Mexico should carefully monitor the progress of this system over the next couple of days. I expect that this system will become a moderate tropical storm, and possibly a minimal hurricane.
Eastern Caribbean tropical wave
A tropical wave located in the eastern Caribbean Sea is interacting with an upper-level trough and generating a large area of cloudiness and showers across the eastern Caribbean and adjacent Windward Islands. Upper-level winds are currently unfavorable for development, but are forecast to become more conducive as the system moves to the WNW at around 15 kt over the next several days. None of the computer models are currently developing this wave, but it bears watching, given that the upper environment could improve over the next couple days (though the general flow looks to remain largely zonal at this point).
Bahamas disturbance
Another disturbance is located over the Bahamas, and is associated with a cold front. Upper-level winds are not currently favorable for development, though they are forecast to improve gradually over the next several days as the system moves little. All in all though, this area is rather unimpressive at the moment, and I suspect that any development will be very slow to occur. The CMC and GFS (operational) are hinting at development of this system in about four days, though they show it, fortunately, recurving out to sea ahead of an upper-level trough. The NOGAPS keeps the ridge stronger, however, which would force the system on a W track into the Gulf of Mexico.
Saturday, July 3, 2010
Tropical weather analysis - July 3, 2010
Invest 95L
Invest 95L continues to struggle amidst unfavorable atmospheric and thermodynamic conditions. Although visible satellite animations indicate that the system has been able to actually generate convection today, this convection is not well organized, and not concentrated near the center. The shower activity associated with the system is displaced well to the south of the improving but still broad surface center, which, based on visible satellite animations and buoy observations, is located near 26N 88W. Upper-level winds are still not all that favorable, with 20 kt of northerly shear impinging upon the center. Additionally, analysis of water vapor animations suggests that the atmosphere in the vicinity of 95L is rather stable. This, along with the aforementioned vertical shear, will tend to limit any appreciable convective activity over the center of the system.
However, the 18z GFS forecasts the upper environment to gradually improve, particularly after 18 hours, and forecasts this to persist for the next several days. This could allow 95L to begin organizing by tomorrow morning, and we will need to keep a careful watch on this system. Currently, the NHC is giving this system a 20% chance of becoming a tropical cyclone within the next 48 hours. Based on the GFS forecast of an improving upper-level environment, however, I will go higher and say 30%. A reconnaissance flight is scheduled for the system tomorrow, if necessary, though it wouldn't surprise me to see it canceled, since even if shear abates by that time, dry air may still be a problem.
This system appears to be moving W at the moment, underneath the influence of a broad ridge to the north. The 12z loop of steering forecasts from PSU indicates that this system should soon come under the influence of a well-defined weakness in the ridge evident from 90W westward for several hundred miles. Hence, I expect 95L to soon turn to the WNW, then gradually bend to the NW and N as it feels this weakness. Based on my forecast track, this system should be inland somewhere along the northwestern Gulf Coast in no more than 48 hours. Right now, I am favoring a track toward extreme southeast Texas, though this could certainly come ashore farther east. Residents from central Texas to southeast Louisiana should carefully monitor the progress of this system over the next couple of days.
Caribbean disturbance
Of more pressing concern than Invest 95L is an area of disturbed weather in the Caribbean, associated with a tropical wave. This system has the potential to become the season's second named storm, and even the second hurricane. Upper-level winds appear favorable for gradual development of this system over the next several days as it moves WNW. The system could impact the Yucatan Peninsula in about three or four days, and subsequently enter the Gulf of Mexico. After that, the GFS and CMC (as per the 12z steering forecasts from PSU's e-wall) differ radically, with the GFS foreseeing a stronger ridge, keeping the system on a more westward path similar to Alex. The latter depicts more troughing in the upper westerlies, which would tend to force the system toward the northern Gulf Coast.
As I said, this system could become another dangerous hurricane in the Gulf of Mexico, and residents there, as well as long the Yucatan Peninsula, should carefully monitor the progress of this system over the next several days.
Invest 95L continues to struggle amidst unfavorable atmospheric and thermodynamic conditions. Although visible satellite animations indicate that the system has been able to actually generate convection today, this convection is not well organized, and not concentrated near the center. The shower activity associated with the system is displaced well to the south of the improving but still broad surface center, which, based on visible satellite animations and buoy observations, is located near 26N 88W. Upper-level winds are still not all that favorable, with 20 kt of northerly shear impinging upon the center. Additionally, analysis of water vapor animations suggests that the atmosphere in the vicinity of 95L is rather stable. This, along with the aforementioned vertical shear, will tend to limit any appreciable convective activity over the center of the system.
However, the 18z GFS forecasts the upper environment to gradually improve, particularly after 18 hours, and forecasts this to persist for the next several days. This could allow 95L to begin organizing by tomorrow morning, and we will need to keep a careful watch on this system. Currently, the NHC is giving this system a 20% chance of becoming a tropical cyclone within the next 48 hours. Based on the GFS forecast of an improving upper-level environment, however, I will go higher and say 30%. A reconnaissance flight is scheduled for the system tomorrow, if necessary, though it wouldn't surprise me to see it canceled, since even if shear abates by that time, dry air may still be a problem.
This system appears to be moving W at the moment, underneath the influence of a broad ridge to the north. The 12z loop of steering forecasts from PSU indicates that this system should soon come under the influence of a well-defined weakness in the ridge evident from 90W westward for several hundred miles. Hence, I expect 95L to soon turn to the WNW, then gradually bend to the NW and N as it feels this weakness. Based on my forecast track, this system should be inland somewhere along the northwestern Gulf Coast in no more than 48 hours. Right now, I am favoring a track toward extreme southeast Texas, though this could certainly come ashore farther east. Residents from central Texas to southeast Louisiana should carefully monitor the progress of this system over the next couple of days.
Caribbean disturbance
Of more pressing concern than Invest 95L is an area of disturbed weather in the Caribbean, associated with a tropical wave. This system has the potential to become the season's second named storm, and even the second hurricane. Upper-level winds appear favorable for gradual development of this system over the next several days as it moves WNW. The system could impact the Yucatan Peninsula in about three or four days, and subsequently enter the Gulf of Mexico. After that, the GFS and CMC (as per the 12z steering forecasts from PSU's e-wall) differ radically, with the GFS foreseeing a stronger ridge, keeping the system on a more westward path similar to Alex. The latter depicts more troughing in the upper westerlies, which would tend to force the system toward the northern Gulf Coast.
As I said, this system could become another dangerous hurricane in the Gulf of Mexico, and residents there, as well as long the Yucatan Peninsula, should carefully monitor the progress of this system over the next several days.
Friday, July 2, 2010
Tropical weather analysis - July 2, 2010
Invest 95L
An extratropical low pressure system recently broke off from the unseasonably deep longwave trough that moved only slowly across the United States over the last several days. This low formed over the Big Bend region of Florida, and has recently moved southwest over the northeastern Gulf of Mexico. This low was designated Invest 95L by the National Hurricane Center today. Visible satellite animations as well as long range doppler radar out of Tallahassee, Florida strongly notes the axis of this low pressure area, centered at approximately 29N 84W. Recent buoy observations indicates that the low pressure area associated with this system is probably not yet at the surface, as surface pressures are high, and not significantly falling.
The lowest I pressure I could find was 29.99 inches from Station SGOF1, which is also located at 29N 84W. Interestingly, the buoy observations, while not at all indicating a closed low, are at least indicating that a broad area of low pressure exists in association with this system. This is a potential sign that 95L is attempting to work this low pressure area down to the surface.
95L is currently experiencing 10 kt of northwesterly vertical shear. This shear appears to be induced by the eastern periphery of a building ridge. However, this shear, based on the aforementioned graph from CIMSS, appears to be located above 300 mb, and 95L's cloud tops do not presently reach anywhere near that high into the atmosphere. Hence, I expect this shear to have little effect on the system.
I expect this system to move SW for the next day or two, followed by a gradual bend to the NW or N after that. On this track, the system will have, at most, 72 hours over water before moving back inland over the northern Gulf Coast. Upper-level winds appear to be only marginally conducive at best, with a band of 15 to 20 kt northerly shear forecast to impinge upon the system throughout most of its existence. Hence, development, if any, will be slow to occur. The National Hurricane Center is giving this system a 10% chance of becoming a tropical cyclone within the next 48 hours, and this is a reasonable forecast. Regardless, residents all along the northern Gulf Coast should carefully monitor the progress of this system over the next several days.
Regardless of development, locally heavy rainfall and strong gusty winds will be possible as the system slowly deepens (since at least some minimal deepening is possible, the aforementioned northerly shear notwithstanding). Note by "deepen", however, I do not necessarily mean "become a tropical cyclone". I'm just saying that I don't feel that the northerly shear is going to be strong enough to prevent the system from lowering its surface pressure a little bit over the next couple days, which will in turn generate deeper convection, which will in turn generate heavy rains and strong winds.
The GFS, UKMET, and ECMWF indicate that an area of low pressure will form along this axis while moving across the northern Gulf of Mexico. The CMC also indicates this, but suggests that it will occur on the Atlantic side, after the system traverses Florida. The CMC solution seems ridiculously unlikely, however, given the currently building ridge to the north of the system. Hence, I have discounted it.
Elsewhere
Elsewhere in the tropics, the reliable ECMWF model is forecasting a tropical depression will form across the western Gulf of Mexico on July 8. The precursor to this system is probably a tropical wave currently analyzed near 40W. I will continue to monitor this system very carefully, as the GFS also indicates some sort of low pressure in the area by 168 hours. The ECMWF nailed the genesis of Alex a week in advance, and it has been consistent with this prediction as well.
The NOGAPS also continues to indicate the possibility of a tropical disturbance across the western Caribbean in the next five days. The instigator to this system is probably a tropical wave currently analyzed along northern South America along 70W. Development in the western Caribbean from this wave appears unlikely for now, based on steering patterns, which take it into the East Pacific.
An extratropical low pressure system recently broke off from the unseasonably deep longwave trough that moved only slowly across the United States over the last several days. This low formed over the Big Bend region of Florida, and has recently moved southwest over the northeastern Gulf of Mexico. This low was designated Invest 95L by the National Hurricane Center today. Visible satellite animations as well as long range doppler radar out of Tallahassee, Florida strongly notes the axis of this low pressure area, centered at approximately 29N 84W. Recent buoy observations indicates that the low pressure area associated with this system is probably not yet at the surface, as surface pressures are high, and not significantly falling.
The lowest I pressure I could find was 29.99 inches from Station SGOF1, which is also located at 29N 84W. Interestingly, the buoy observations, while not at all indicating a closed low, are at least indicating that a broad area of low pressure exists in association with this system. This is a potential sign that 95L is attempting to work this low pressure area down to the surface.
95L is currently experiencing 10 kt of northwesterly vertical shear. This shear appears to be induced by the eastern periphery of a building ridge. However, this shear, based on the aforementioned graph from CIMSS, appears to be located above 300 mb, and 95L's cloud tops do not presently reach anywhere near that high into the atmosphere. Hence, I expect this shear to have little effect on the system.
I expect this system to move SW for the next day or two, followed by a gradual bend to the NW or N after that. On this track, the system will have, at most, 72 hours over water before moving back inland over the northern Gulf Coast. Upper-level winds appear to be only marginally conducive at best, with a band of 15 to 20 kt northerly shear forecast to impinge upon the system throughout most of its existence. Hence, development, if any, will be slow to occur. The National Hurricane Center is giving this system a 10% chance of becoming a tropical cyclone within the next 48 hours, and this is a reasonable forecast. Regardless, residents all along the northern Gulf Coast should carefully monitor the progress of this system over the next several days.
Regardless of development, locally heavy rainfall and strong gusty winds will be possible as the system slowly deepens (since at least some minimal deepening is possible, the aforementioned northerly shear notwithstanding). Note by "deepen", however, I do not necessarily mean "become a tropical cyclone". I'm just saying that I don't feel that the northerly shear is going to be strong enough to prevent the system from lowering its surface pressure a little bit over the next couple days, which will in turn generate deeper convection, which will in turn generate heavy rains and strong winds.
The GFS, UKMET, and ECMWF indicate that an area of low pressure will form along this axis while moving across the northern Gulf of Mexico. The CMC also indicates this, but suggests that it will occur on the Atlantic side, after the system traverses Florida. The CMC solution seems ridiculously unlikely, however, given the currently building ridge to the north of the system. Hence, I have discounted it.
Elsewhere
Elsewhere in the tropics, the reliable ECMWF model is forecasting a tropical depression will form across the western Gulf of Mexico on July 8. The precursor to this system is probably a tropical wave currently analyzed near 40W. I will continue to monitor this system very carefully, as the GFS also indicates some sort of low pressure in the area by 168 hours. The ECMWF nailed the genesis of Alex a week in advance, and it has been consistent with this prediction as well.
The NOGAPS also continues to indicate the possibility of a tropical disturbance across the western Caribbean in the next five days. The instigator to this system is probably a tropical wave currently analyzed along northern South America along 70W. Development in the western Caribbean from this wave appears unlikely for now, based on steering patterns, which take it into the East Pacific.
Subscribe to:
Comments (Atom)