Alex
Hurricane Alex is poised to make landfall in northeastern Mexico probably within the next 20 minutes. Landfall will occur about 100 miles south of Brownsville. As of the 7:00 PM CDT intermediate advisory from the National Hurricane Center, the hurricane had maximum sustained winds of 100 mph, a Category 2 hurricane, and was located at 24.3N 97.5W. Additionally, the movement was toward the W at 12 mph, and the pressure was at 950 mb. This pressure is more typical of a Category 3 hurricane, but again, because Alex is a large storm, and its energy spans a large area, it has effectively minimized the otherwise steep pressure gradient that would be associated with an ordinary, smaller tropical cyclone. Reconnaissance aircraft reported an outer wind maxima within the hurricane this afternoon, and that undoubtedly halted any rapid intensification of the storm.
Alex does not have time to intensify further, and will make landfall about 100 miles south of Brownsville as a Category 2 hurricane with 100 mph sustained winds. After landfall, expect rapid weakening of the inner core, but the outer core will probably take considerable time to weaken, as will the overall circulation envelope, even within the core of the hurricane. This is because Alex is a tremendously large storm, and its overall circulation influences a very large area. Hence, heavy rainfall will continue to be a possibility across portions of the western and northern Gulf of Mexico, even after Alex is already well inland and weakening. This heavy rain threat should persist until at least sometime tomorrow night.
Long-range radar from Brownsville, Texas shows that Alex will be making landfall soon, as I said. It also shows, impressively, that the hurricane is generating outer rain bands over a very large swath of real estate, with bands stretching all the way from its landfall location to southeastern Louisiana. Already, Alex has spawned a total of five tornadoes across the state of Texas, including three in south Texas, one in central Texas, and one in southeast Texas. The Storm Prediction Center in Norman, Oklahoma, has issued a tornado watch for extreme southern Texas, and adjacent coastal waters, effective since 7:45 PM CDT. The watch is forecast to be maintained until 4:00 AM CDT Thursday morning.
Another big impact from Alex will be torrential rains, well away from its center. These rains will likely produce some flash flooding across portions of southern Texas, as well as a good portion of northeastern, northern, and central Mexico over the next couple of days. These rains could prove particularly deadly across the enormously high mountains of Sierra Madre Oriental, where in addition to flash flooding, mud/landslides will be a possibility.
Another factor is storm surge. The National Hurricane Center is predicting that Alex will bring storm surges in excess of 4 to 6 feet above normal along the immediate coast to the north of where the eye makes landfall. As is always the case with landfalling hurricanes, the surge could penetrate up to several miles inland from the coast, inundating some areas (though the surge does steadily decrease in depth as it travels inland). In addition to the storm surge, large, battering waves will lash a large swath of the Gulf Coast from northeast Mexico all the way to the northern Gulf Coast (obviously, these waves will be lesser in magnitude the farther away from the center one is).
I am expecting Alex to be worse than 2008's Hurricane Dolly, which made landfall in extreme south Texas as an 85 mph Category 1 hurricane. I expect this not necessarily because of Alex's intensity, but because of its tremendously large size. The overall circulation covers a much larger area than Dolly did.
Elsewhere in the tropics
Elsewhere, all is quiet in the Atlantic. The extratropical surface low that the GFS and GFDL (and previously, the HWRF, as well) were forecasting would branch off along the northern Gulf Coast from the longwave trough is not present in any of the model fields today.
The NOGAPS, however, is predicting that a tropical disturbance will form in the western Caribbean in about five days. No other models are showing this, though most other models do show an increase in moisture in the area during this time, so it bears watching.
Wednesday, June 30, 2010
Tuesday, June 29, 2010
Tropical weather analysis - June 29, 2010
Alex
Tropical Storm Alex is on the verge of becoming a hurricane, with recentAMSU-B microwave satellite data measuring a partial eyewall, though this is still about half open, according to the aforementioned AMSU-B pass. As of the 7:00 PM CDT intermediate advisory from the National Hurricane Center, Alex is located near 23.2N 94.5W, moving WNW at 12 mph. Maximum sustained winds were near 70 mph, and the central pressure at 980 mb. Alex has a rather low pressure for a mere tropical storm, but this is because larger storms such as this one tend to not produce much of a pressure gradient, because their energy spans a much greater distance (remember, pressure gradients generate wind speeds, not central pressure).
This was most recently the case with 2008's Hurricane Ike, also an exceptionally large storm. Infrared satellite loops also indicate a gradual increase in overall organization, though upper-level outflow still appears to be restricted to the northwest. This is probably due to dry air entrainment, as there are several noticeable gaps within the convection, particularly along the northwestern side.
However, water vapor animations suggest that any dry air affecting Alex will not produce any appreciable negative effect upon the cyclone's intensity, though the dry air currently seen over Texas and Mexico might begin to slow intensification as Alex gets closer to the coast. My forecast track, based on CIMSS steering data for 400 mb, along with water vapor animations, steering data from PSU, and model data, indicates a landfall north of Tampico, but well to the south of Brownsville, Texas. This forecast is in best agreement with the 18z run of the GFS model, taking the cyclone NW for the first 6-12 hours, then WNW, then W as it nears landfall. It is also similar, though not identical, to the NHC's official forecast. However, this could still be too far to the north, as the ridge appears to be quite strong -- stronger than previously forecast, even.
Upper-level winds appear conducive for steady intensification of Alex, until landfall occurs in just over 30 hours. However, as I said earlier, dry air ingestion may be a problem as Alex gets closer to the coast. Nonetheless, I am not expecting this to be able to deter the cyclone from intensifying entirely. At most, it should only slow intensification as the cyclone nears the coast. Alex appears poised to pass underneath a warm eddy located from about 22.5N to 24N. This should occur within the next several hours. TCHP will decrease as Alex pulls away from this region, but will still be sufficiently abundant as to aid in continued intensification up until landfall. I am still forecasting Alex to attain Category 2 status before landfall, and there is still a small chance (10%) that it could attain major hurricane status.
As far as watches and warnings goes, as of 7:00 PM CDT, a hurricane warning is in effect for:
- The Texas coast south of Baffin Bay to the mouth of the Rio Grande
- The coast of Mexico from the mouth of the Rio Grande to La Cruz
As of 7:00 PM CDT, a tropical storm watch is in effect for:
- The coast of Texas from Baffin Bay to Port O'Connor.
- The coast of Mexico south of La Cruz to Cabo Rojo.
As far as watches and warnings goes, as of 7:00 PM CDT, a hurricane warning is in effect for:
- The Texas coast south of Baffin Bay to the mouth of the Rio Grande
- The coast of Mexico from the mouth of the Rio Grande to La Cruz
As of 7:00 PM CDT, a tropical storm watch is in effect for:
- The coast of Texas from Baffin Bay to Port O'Connor.
- The coast of Mexico south of La Cruz to Cabo Rojo.
Elsewhere
Elsewhere in the tropics, the GFS and GFDL are forecasting that an extratropical surface low will break off from the unseasonably strong longwave trough currently moving across the United States. This is forecast to occur in four days somewhere off the northern Gulf Coast from the western Florida panhandle westward to the mouth of the Mississippi River. Upper-level winds do not appear all that conducive for strengthening, and the system will probably be too close to land to form a deep warm core, anyway.
Tropical Storm Alex is on the verge of becoming a hurricane, with recentAMSU-B microwave satellite data measuring a partial eyewall, though this is still about half open, according to the aforementioned AMSU-B pass. As of the 7:00 PM CDT intermediate advisory from the National Hurricane Center, Alex is located near 23.2N 94.5W, moving WNW at 12 mph. Maximum sustained winds were near 70 mph, and the central pressure at 980 mb. Alex has a rather low pressure for a mere tropical storm, but this is because larger storms such as this one tend to not produce much of a pressure gradient, because their energy spans a much greater distance (remember, pressure gradients generate wind speeds, not central pressure).
This was most recently the case with 2008's Hurricane Ike, also an exceptionally large storm. Infrared satellite loops also indicate a gradual increase in overall organization, though upper-level outflow still appears to be restricted to the northwest. This is probably due to dry air entrainment, as there are several noticeable gaps within the convection, particularly along the northwestern side.
However, water vapor animations suggest that any dry air affecting Alex will not produce any appreciable negative effect upon the cyclone's intensity, though the dry air currently seen over Texas and Mexico might begin to slow intensification as Alex gets closer to the coast. My forecast track, based on CIMSS steering data for 400 mb, along with water vapor animations, steering data from PSU, and model data, indicates a landfall north of Tampico, but well to the south of Brownsville, Texas. This forecast is in best agreement with the 18z run of the GFS model, taking the cyclone NW for the first 6-12 hours, then WNW, then W as it nears landfall. It is also similar, though not identical, to the NHC's official forecast. However, this could still be too far to the north, as the ridge appears to be quite strong -- stronger than previously forecast, even.
Upper-level winds appear conducive for steady intensification of Alex, until landfall occurs in just over 30 hours. However, as I said earlier, dry air ingestion may be a problem as Alex gets closer to the coast. Nonetheless, I am not expecting this to be able to deter the cyclone from intensifying entirely. At most, it should only slow intensification as the cyclone nears the coast. Alex appears poised to pass underneath a warm eddy located from about 22.5N to 24N. This should occur within the next several hours. TCHP will decrease as Alex pulls away from this region, but will still be sufficiently abundant as to aid in continued intensification up until landfall. I am still forecasting Alex to attain Category 2 status before landfall, and there is still a small chance (10%) that it could attain major hurricane status.
As far as watches and warnings goes, as of 7:00 PM CDT, a hurricane warning is in effect for:
- The Texas coast south of Baffin Bay to the mouth of the Rio Grande
- The coast of Mexico from the mouth of the Rio Grande to La Cruz
As of 7:00 PM CDT, a tropical storm watch is in effect for:
- The coast of Texas from Baffin Bay to Port O'Connor.
- The coast of Mexico south of La Cruz to Cabo Rojo.
As far as watches and warnings goes, as of 7:00 PM CDT, a hurricane warning is in effect for:
- The Texas coast south of Baffin Bay to the mouth of the Rio Grande
- The coast of Mexico from the mouth of the Rio Grande to La Cruz
As of 7:00 PM CDT, a tropical storm watch is in effect for:
- The coast of Texas from Baffin Bay to Port O'Connor.
- The coast of Mexico south of La Cruz to Cabo Rojo.
Elsewhere
Elsewhere in the tropics, the GFS and GFDL are forecasting that an extratropical surface low will break off from the unseasonably strong longwave trough currently moving across the United States. This is forecast to occur in four days somewhere off the northern Gulf Coast from the western Florida panhandle westward to the mouth of the Mississippi River. Upper-level winds do not appear all that conducive for strengthening, and the system will probably be too close to land to form a deep warm core, anyway.
Monday, June 28, 2010
Tropical weather analysis - June 28, 2010
Tropical Storm Alex has only gradually intensified today. At the 7:00 PM CDT intermediate advisory from the National Hurricane Center, Alex's maximum sustained winds estimated at 60 mph, its central pressure at 990 mb, and its movement stationary. Additionally, it was located at 20.6N 91.6W. The last of the visible satellite animations depict that Alex may be beginning to overcome the dry air evident on water vapor animations, as deep convection is attempting to wrap cyclonically into the western half of the circulation, something that has been considerably lacking today.
The likely causes for the cyclone's slow intensification today is 20 kt of northwesterly vertical shear, analyzed by University of Wisconsin CIMSS, the aforementioned dry air punching into the storm from the west, and cold water upwelling, as the longer strong winds persist over a given area of ocean, particularly along shallow shelf waters a la offshore the western Yucatan Peninsula, the more cold water is stirred up from the depths, and brought to the surface. I expect that later tonight and into Tuesday morning, as Alex begins to actually move, it will resume intensification. Indeed, I find it quite likely that Alex will be a hurricane by mid Tuesday morning.
In any case, it's time to focus on the track forecast for Alex. Fortunately, the computer models have come into much better agreement today on Alex's final landfall location, with the majority of them calling for a landfall in northeastern Mexico. The GFS and HWRF are the only models, as per 18z, that are calling for a Texas landfall, with the former depicting a landfall between Port Mansfield and Corpus Christi, and the latter depicting one just north of Port Mansfield. An averaging out of the model forecasts leads to a landfall near Brownsville, Texas. CIMSS steering analysis from 500 to 400 mb indicates that a NNW motion should begin within the next few hours, albeit a slow one.
The models also generally agree with this. By around 24 hours, it is generally agreed upon by the models that Alex will begin moving WNW as the ridge builds back in the wake of an unseasonably strong longwave trough currently moving across much of the central and eastern United States. Water vapor imagery indicates that the trough isn't digging far enough southward as to give Alex a significant poleward movement, and any poleward movement will be short-lived (24 hours), and Alex will not be able to get very far in that direction, due to its slow movement.
After 24 hours, as I said, the cyclone should turn back to the WNW, and possibly NW in the wake of a building ridge. I'm going with WNW though, because I don't see the rebuilt ridge having any significant weakness in it. How far north Alex gets before steering currents restrengthen is critical to just where it will make its final landfall. Right now, I think the most likely location is Brownsville, but residents from Tampico to just north of Corpus Christi should carefully monitor the progress of Alex over the next couple of days.
As of 4:00 PM CDT, a hurricane watch is in effect for the following:
- The Texas coast south of Baffin Bay to the mouth of the Rio Grande
- The coast of Mexico from the mouth of the Rio Grande to La Cruz
As of 4:00 PM CDT, a tropical storm watch is in effect for the following:
- The Texas coast from Baffin Bay to Port O'Connor.
There are currently no hurricane warnings posted, but this could change later tonight or early Tuesday morning, as the landfall location of Alex becomes more clear. Residents within the watch area should rush their preparation plans to completion. Also, always heed local law enforcement officials during natural disasters such as this.
The intensity forecast is fairly straightforward. By 24 hours, Alex could be located over SSTs as high as 29C. More importantly, oceanic heat content increases sharply along the forecast track beginning at 23N. Oceanic heat content is a fancy term for warm water that extends to great depth. These waters, not the shallow waters that Alex is currently sitting over, are crucial to intensification of a tropical cyclone.
Alex will be entering an area of oceanic heat content in about 24 hours. This high octane fuel will continue to be present up until just before landfall, which, based on a general consensus of the models, should be sometime on early Thursday morning. The farther north Alex goes, the longer landfall will be delayed, and vice versa. However, landfall will certainly occur no later than Thursday evening, and no earlier than Wednesday night.
Based on the continued forecast of low shear from the GFS, I find it likely that Alex will steadily intensify to a Category 2 hurricane, and make landfall at that intensity. There also remains an outside chance of Alex becoming a Category 3 hurricane.
The likely causes for the cyclone's slow intensification today is 20 kt of northwesterly vertical shear, analyzed by University of Wisconsin CIMSS, the aforementioned dry air punching into the storm from the west, and cold water upwelling, as the longer strong winds persist over a given area of ocean, particularly along shallow shelf waters a la offshore the western Yucatan Peninsula, the more cold water is stirred up from the depths, and brought to the surface. I expect that later tonight and into Tuesday morning, as Alex begins to actually move, it will resume intensification. Indeed, I find it quite likely that Alex will be a hurricane by mid Tuesday morning.
In any case, it's time to focus on the track forecast for Alex. Fortunately, the computer models have come into much better agreement today on Alex's final landfall location, with the majority of them calling for a landfall in northeastern Mexico. The GFS and HWRF are the only models, as per 18z, that are calling for a Texas landfall, with the former depicting a landfall between Port Mansfield and Corpus Christi, and the latter depicting one just north of Port Mansfield. An averaging out of the model forecasts leads to a landfall near Brownsville, Texas. CIMSS steering analysis from 500 to 400 mb indicates that a NNW motion should begin within the next few hours, albeit a slow one.
The models also generally agree with this. By around 24 hours, it is generally agreed upon by the models that Alex will begin moving WNW as the ridge builds back in the wake of an unseasonably strong longwave trough currently moving across much of the central and eastern United States. Water vapor imagery indicates that the trough isn't digging far enough southward as to give Alex a significant poleward movement, and any poleward movement will be short-lived (24 hours), and Alex will not be able to get very far in that direction, due to its slow movement.
After 24 hours, as I said, the cyclone should turn back to the WNW, and possibly NW in the wake of a building ridge. I'm going with WNW though, because I don't see the rebuilt ridge having any significant weakness in it. How far north Alex gets before steering currents restrengthen is critical to just where it will make its final landfall. Right now, I think the most likely location is Brownsville, but residents from Tampico to just north of Corpus Christi should carefully monitor the progress of Alex over the next couple of days.
As of 4:00 PM CDT, a hurricane watch is in effect for the following:
- The Texas coast south of Baffin Bay to the mouth of the Rio Grande
- The coast of Mexico from the mouth of the Rio Grande to La Cruz
As of 4:00 PM CDT, a tropical storm watch is in effect for the following:
- The Texas coast from Baffin Bay to Port O'Connor.
There are currently no hurricane warnings posted, but this could change later tonight or early Tuesday morning, as the landfall location of Alex becomes more clear. Residents within the watch area should rush their preparation plans to completion. Also, always heed local law enforcement officials during natural disasters such as this.
The intensity forecast is fairly straightforward. By 24 hours, Alex could be located over SSTs as high as 29C. More importantly, oceanic heat content increases sharply along the forecast track beginning at 23N. Oceanic heat content is a fancy term for warm water that extends to great depth. These waters, not the shallow waters that Alex is currently sitting over, are crucial to intensification of a tropical cyclone.
Alex will be entering an area of oceanic heat content in about 24 hours. This high octane fuel will continue to be present up until just before landfall, which, based on a general consensus of the models, should be sometime on early Thursday morning. The farther north Alex goes, the longer landfall will be delayed, and vice versa. However, landfall will certainly occur no later than Thursday evening, and no earlier than Wednesday night.
Based on the continued forecast of low shear from the GFS, I find it likely that Alex will steadily intensify to a Category 2 hurricane, and make landfall at that intensity. There also remains an outside chance of Alex becoming a Category 3 hurricane.
Sunday, June 27, 2010
Tropical weather analysis - June 27, 2010 - second edition
Began writing at approximately 7:47 PM EDT
Alex weakened to a tropical depression this morning during its prolonged passage over Belize and the Yucatan Peninsula. As of the 4:00 PM CDT advisory from the National Hurricane Center, Alex's center was estimated to be near 19.2N 90.9W, moving WNW at 9 mph. Maximum sustained winds were 30 kt (35 mph), and the central pressure 999 mb. Visible satellite loops show that Alex has continued moving WNW since the issuance of the previous advisory, and is now located just inland from the western Yucatan Peninsula, and is ready to emerge into the Bay of Campeche around 60 miles southwest Campeche, Mexico. Alex should begin moving NW very soon, as CIMSS steering as well as water vapor animations suggest that a weakness is evident within the subtropical ridge around 89W.
It will be interesting to see how Alex responds to this weakness over the next several hours. So far, no northwesterly component of motion has been observed with Alex. However, I am nonetheless expecting a NW to NNW motion to begin soon, persisting for the next 6-12 hours, after which point it should once again commit to a more westward track.
The biggest question regarding Alex continues to be track, not intensity, since the latter is fairly straightforward in this case. The models agree on Alex moving only very slowly across the Bay of Campeche for the first couple of days, owing to a weak steering regime imparted by a vigorous longwave trough currently stretching from the high plains all the way to the southwestern United States. There is some southwesterly mid to upper flow already evident across the northwestern Gulf of Mexico, as per water vapor loops. However, this flow appears to be quite weak at the moment, and is not enough to fully erode the ridge so that Alex gains a significant amount of latitude, at least in the near-term (again, I expect a NW to NNW motion for the next 6-12 hours, followed by a more westerly component after that, albeit slowly).
At the moment, it is difficult to assess the likely evolution of the aforementioned trough beyond, say, 24 hours. Thus, I will hold off on doing so. Instead, I will split difference between the various models, which all foresee Alex moving painfully slowly across the Bay of Campeche, particularly after 24 hours, with a more solid steering regime influencing the cyclone beginning in about 60 to 72 hours. Where they differ, obviously, is whether or not the trough or the ridge will steer Alex to its final landfall during this time.
Again, it's not easy to tell at this point which solution will be correct. Were I to hazard a guess though, based on water vapor imagery alone, it would be that the GFS and CMC continue to be much too poleward, particularly the latter, which depicts as a landfall in western Louisiana. Instead, I will split the difference between the various models and forecast a landfall along the south-central Texas coast. I am in best agreement with the 18z HWRF, track-wise. Should this forecast end up being correct, Corpus Christi would be under the gun for a possible direct hit from then Hurricane Alex.
However, the forecast is highly uncertain at this time, and is subject to change. The threat to Brownsville southward to Tampico is not really minimized at present, so residents there need not let their guard down. Given the large amount of uncertainty in this forecast, residents from Tampico, Mexico to Cameron, Louisiana should closely monitor the progress of Alex over the next several days.
The intensity forecast, as I said, is much simpler. The GFS, which has performed exceptionally well with the evolution of the anticyclone, continues to depict an anticyclonic environment across the western Gulf of Mexico. And, although the aforementioned anticyclone is not directly atop Alex at the moment, the GFS brings it to the vicinity of the cyclone within about 24 hours. Given the fact that the anticyclone is not currently centered over Alex, the fact that TCHP is very low off the immediate coast of the western Yucatan Peninsula, as well as the fact that it typically takes a cyclone at least 24 hours to recover its inner core after prolonged passage overland, I am not expecting significant intensification of Alex over the next day or so, and any abrupt intensification of the cyclone during this time will be from the winds catching up to the already very low central pressure.
Thereafter, as Alex moves underneath the anticyclone and into warmer waters, more steady, possibly rapid intensification appears to be in order, under a light upper-level wind flow. The timing of landfall is not completely certain, but is generally agreed by the models to be sometime on Thursday morning. Hence, I will forecast a landfall of Alex on Thursday morning. I do not want to deviate to a more poleward track just yet, at least until I see how the trough continues to unfold.
I expect Alex to be at hurricane intensity at landfall, and it could even be a Category 2. A Category 3 is even possible, but the likelihood of this happening appears rather slim at the moment.
Alex weakened to a tropical depression this morning during its prolonged passage over Belize and the Yucatan Peninsula. As of the 4:00 PM CDT advisory from the National Hurricane Center, Alex's center was estimated to be near 19.2N 90.9W, moving WNW at 9 mph. Maximum sustained winds were 30 kt (35 mph), and the central pressure 999 mb. Visible satellite loops show that Alex has continued moving WNW since the issuance of the previous advisory, and is now located just inland from the western Yucatan Peninsula, and is ready to emerge into the Bay of Campeche around 60 miles southwest Campeche, Mexico. Alex should begin moving NW very soon, as CIMSS steering as well as water vapor animations suggest that a weakness is evident within the subtropical ridge around 89W.
It will be interesting to see how Alex responds to this weakness over the next several hours. So far, no northwesterly component of motion has been observed with Alex. However, I am nonetheless expecting a NW to NNW motion to begin soon, persisting for the next 6-12 hours, after which point it should once again commit to a more westward track.
The biggest question regarding Alex continues to be track, not intensity, since the latter is fairly straightforward in this case. The models agree on Alex moving only very slowly across the Bay of Campeche for the first couple of days, owing to a weak steering regime imparted by a vigorous longwave trough currently stretching from the high plains all the way to the southwestern United States. There is some southwesterly mid to upper flow already evident across the northwestern Gulf of Mexico, as per water vapor loops. However, this flow appears to be quite weak at the moment, and is not enough to fully erode the ridge so that Alex gains a significant amount of latitude, at least in the near-term (again, I expect a NW to NNW motion for the next 6-12 hours, followed by a more westerly component after that, albeit slowly).
At the moment, it is difficult to assess the likely evolution of the aforementioned trough beyond, say, 24 hours. Thus, I will hold off on doing so. Instead, I will split difference between the various models, which all foresee Alex moving painfully slowly across the Bay of Campeche, particularly after 24 hours, with a more solid steering regime influencing the cyclone beginning in about 60 to 72 hours. Where they differ, obviously, is whether or not the trough or the ridge will steer Alex to its final landfall during this time.
Again, it's not easy to tell at this point which solution will be correct. Were I to hazard a guess though, based on water vapor imagery alone, it would be that the GFS and CMC continue to be much too poleward, particularly the latter, which depicts as a landfall in western Louisiana. Instead, I will split the difference between the various models and forecast a landfall along the south-central Texas coast. I am in best agreement with the 18z HWRF, track-wise. Should this forecast end up being correct, Corpus Christi would be under the gun for a possible direct hit from then Hurricane Alex.
However, the forecast is highly uncertain at this time, and is subject to change. The threat to Brownsville southward to Tampico is not really minimized at present, so residents there need not let their guard down. Given the large amount of uncertainty in this forecast, residents from Tampico, Mexico to Cameron, Louisiana should closely monitor the progress of Alex over the next several days.
The intensity forecast, as I said, is much simpler. The GFS, which has performed exceptionally well with the evolution of the anticyclone, continues to depict an anticyclonic environment across the western Gulf of Mexico. And, although the aforementioned anticyclone is not directly atop Alex at the moment, the GFS brings it to the vicinity of the cyclone within about 24 hours. Given the fact that the anticyclone is not currently centered over Alex, the fact that TCHP is very low off the immediate coast of the western Yucatan Peninsula, as well as the fact that it typically takes a cyclone at least 24 hours to recover its inner core after prolonged passage overland, I am not expecting significant intensification of Alex over the next day or so, and any abrupt intensification of the cyclone during this time will be from the winds catching up to the already very low central pressure.
Thereafter, as Alex moves underneath the anticyclone and into warmer waters, more steady, possibly rapid intensification appears to be in order, under a light upper-level wind flow. The timing of landfall is not completely certain, but is generally agreed by the models to be sometime on Thursday morning. Hence, I will forecast a landfall of Alex on Thursday morning. I do not want to deviate to a more poleward track just yet, at least until I see how the trough continues to unfold.
I expect Alex to be at hurricane intensity at landfall, and it could even be a Category 2. A Category 3 is even possible, but the likelihood of this happening appears rather slim at the moment.
Saturday, June 26, 2010
Tropical weather analysis - June 27, 2010
Tropical Storm Alex made landfall just north of Belize City, Belize as a 55 kt (65 mph) tropical storm early this evening. At the time of landfall, Alex appeared to be organizing into a hurricane, with a warm spot evident within the midst of the well-defined central dense overcast (CDO). As per the 10:00 PM CDT advisory from the National Hurricane Center, Alex was centered near 17.7N 88.4W, moving WNW at 12 mph, had maximum sustained winds of 50 kt (60 mph), and a pressure of 997 mb. Alex still appears to be moving WNW at this present time, though at the time of this analysis I place the center at 17N 89W, as opposed to 88W. Not because the NHC was wrong, but because the system has since moved a bit farther inland. Based on steering currents from CIMSS, I foresee Alex moving NW very soon, steered by southeasterly flow along the southwestern periphery of a persistent ridge.
Obviously, the longer Alex moves WNW, the more land it will encounter, and the weaker it will be when it emerges into the southern Gulf of Mexico in a couple of days. Alex should emerge into the southern Gulf of Mexico in about 30 hours, but not before bringing flooding rains to Belize and portions of the Yucatan Peninsula. Though I mentioned yesterday that Alex could simply dissipate over the Yucatan, I am not expecting that to happen at this time, even if it's passing over some more rugged terrain than was previously forecast. Why? Because Alex is an exceptionally large storm, has a well-defined anticyclonic outflow pattern aloft, and abundant convection. Large systems take considerable time to wind down. Thereafter, models are widely divergent -- much more so than they were this time yesterday.
As per 18z, the GFS and GFDL both bring the system into Texas, with the GFS taking Alex to the central Texas coast in 168 hours, and the GFDL to the upper Texas coast as a Category 3 in just under five days. As per 12z (still awaiting the 0z run), the CMC is mimicking the GFS, albeit slightly farther south, and at a much earlier time -- around 108 hours.
The HWRF, NOGAPS, UKMET, and ECMWF all bring the system into central Mexico in about three to four days. Given the weak steering flow expected across that portion of the Gulf expected across the southern Gulf from 36 to at least 72 hours, I tend to lean toward a landfall on late Wednesday or early Thursday. There is still considerable uncertainty as to where Alex will ultimately make its second landfall, as I displayed above (with the two divergent model camps). The key player in this scenario will be an upper-level trough, analyzed very well on water vapor loops. It does appear that this trough is dipping quite far to the south -- much farther than the models were indicating this time yesterday. Because of this, it is possible that Alex gains some latitude after emerging into the Bay of Campeche in about 30 hours. How much latitude, obviously, will depend upon the evolution of the aforementioned upper trough.
A stronger Alex would be more inclined to respond to the trough by moving poleward, while a weaker cyclone would be more inclined to stall until the trough bypasses it to the north, and the ridge rebuilds in the wake of the trough. I do not think, however, that Alex will gain enough latitude to appreciably affect the oil spill region, and will probably not even as gain as much latitude as the 18z GFDL is predicting.
I will not forecast a significant increase in latitude at this time, however, since it remains to be seen just how the trough will evolve and how strong Alex will be within 30 hours or so -- the time it is expected to arrive within the Bay of Campeche. Given the greater than normal uncertainty in this forecast, residents from Veracruz to Houston should carefully monitor the progress of Alex over the next several days (though I place less emphasis on Houston than points farther south along the Texas coast -- but just as a precautionary measure). At this time, I will go with the NHC's forecast, albeit slightly farther north.
It should also be noted that Alex is a large circulation. Because of this, the farther north Alex makes its final landfall, the more energy will be pulled eastward -- it will have a lot of energy to work with, even after dissipation -- large systems do not die easily. Hence, heavy, possibly flooding rainfall, will be possible across portions of Texas and Louisiana even after dissipation of Alex as a tropical cyclone -- provided, of course, it gains some unforeseen (by the NHC) latitude. Even if not, the western half of Texas will certainly see some remnant moisture from this system.
As far as intensity goes, I agree pretty well with the NHC's current thinking, bringing the system to hurricane status within 72 hours. It typically takes around 24 hours for a tropical cyclone to reorganize its inner core after prolonged passage overland. Hence, I do not foresee significant intensification of Alex for the first 24 hours after emergence into the Bay of Campeche. The intensity forecast isn't as clear cut as I might have made it seem, however, because the GFS and ECMWF are still divided on the vertical shear forecast, and also because Alex's ultimate final landfall location is still uncertain at this point.
The GFS keeps a strongly anticyclonic environment across the western and west-central Gulf of Mexico, which would obviously favor intensification. The ECMWF, on the other hand, while lifting the shear out of the southwestern Gulf, still keeps some shear across the western and west-central Gulf, and a largely zonal flow, to boot. This would greatly hamper intensification of Alex. However, given that the GFS seems to be the more reliable model with shear profiles, particularly lately, I will go with it and forecast strengthening as Alex emerges into the Bay of Campeche.
How much depends not only track, but on the timing of landfall, as well. I have delayed the system's landfall a bit, in comparison to the NHC, however, and I expect a landfall on late Wednesday night. This forecast will have to be adjusted accordingly as we witness the evolution and progression of the upper trough. So the later Alex comes in, the greater chance it will have to intensify.
Also of note is the TCHP, which, as per the graph above, is quite high across the western Gulf of Mexico, certainly enough to generate a Category 2 hurricane, provided upper-level conditions allow, of course. Should Alex move farther north than forecast, it will have a chance to intensify more than is currently forecast by me or the NHC. Given the uncertainty, however, I'll only go with a minimal hurricane within 72 hours, and an intensifying Category 1 at landfall, which I expect to occur a bit to the north of Tampico, Mexico.
Obviously, the longer Alex moves WNW, the more land it will encounter, and the weaker it will be when it emerges into the southern Gulf of Mexico in a couple of days. Alex should emerge into the southern Gulf of Mexico in about 30 hours, but not before bringing flooding rains to Belize and portions of the Yucatan Peninsula. Though I mentioned yesterday that Alex could simply dissipate over the Yucatan, I am not expecting that to happen at this time, even if it's passing over some more rugged terrain than was previously forecast. Why? Because Alex is an exceptionally large storm, has a well-defined anticyclonic outflow pattern aloft, and abundant convection. Large systems take considerable time to wind down. Thereafter, models are widely divergent -- much more so than they were this time yesterday.
As per 18z, the GFS and GFDL both bring the system into Texas, with the GFS taking Alex to the central Texas coast in 168 hours, and the GFDL to the upper Texas coast as a Category 3 in just under five days. As per 12z (still awaiting the 0z run), the CMC is mimicking the GFS, albeit slightly farther south, and at a much earlier time -- around 108 hours.
The HWRF, NOGAPS, UKMET, and ECMWF all bring the system into central Mexico in about three to four days. Given the weak steering flow expected across that portion of the Gulf expected across the southern Gulf from 36 to at least 72 hours, I tend to lean toward a landfall on late Wednesday or early Thursday. There is still considerable uncertainty as to where Alex will ultimately make its second landfall, as I displayed above (with the two divergent model camps). The key player in this scenario will be an upper-level trough, analyzed very well on water vapor loops. It does appear that this trough is dipping quite far to the south -- much farther than the models were indicating this time yesterday. Because of this, it is possible that Alex gains some latitude after emerging into the Bay of Campeche in about 30 hours. How much latitude, obviously, will depend upon the evolution of the aforementioned upper trough.
A stronger Alex would be more inclined to respond to the trough by moving poleward, while a weaker cyclone would be more inclined to stall until the trough bypasses it to the north, and the ridge rebuilds in the wake of the trough. I do not think, however, that Alex will gain enough latitude to appreciably affect the oil spill region, and will probably not even as gain as much latitude as the 18z GFDL is predicting.
I will not forecast a significant increase in latitude at this time, however, since it remains to be seen just how the trough will evolve and how strong Alex will be within 30 hours or so -- the time it is expected to arrive within the Bay of Campeche. Given the greater than normal uncertainty in this forecast, residents from Veracruz to Houston should carefully monitor the progress of Alex over the next several days (though I place less emphasis on Houston than points farther south along the Texas coast -- but just as a precautionary measure). At this time, I will go with the NHC's forecast, albeit slightly farther north.
It should also be noted that Alex is a large circulation. Because of this, the farther north Alex makes its final landfall, the more energy will be pulled eastward -- it will have a lot of energy to work with, even after dissipation -- large systems do not die easily. Hence, heavy, possibly flooding rainfall, will be possible across portions of Texas and Louisiana even after dissipation of Alex as a tropical cyclone -- provided, of course, it gains some unforeseen (by the NHC) latitude. Even if not, the western half of Texas will certainly see some remnant moisture from this system.
As far as intensity goes, I agree pretty well with the NHC's current thinking, bringing the system to hurricane status within 72 hours. It typically takes around 24 hours for a tropical cyclone to reorganize its inner core after prolonged passage overland. Hence, I do not foresee significant intensification of Alex for the first 24 hours after emergence into the Bay of Campeche. The intensity forecast isn't as clear cut as I might have made it seem, however, because the GFS and ECMWF are still divided on the vertical shear forecast, and also because Alex's ultimate final landfall location is still uncertain at this point.
The GFS keeps a strongly anticyclonic environment across the western and west-central Gulf of Mexico, which would obviously favor intensification. The ECMWF, on the other hand, while lifting the shear out of the southwestern Gulf, still keeps some shear across the western and west-central Gulf, and a largely zonal flow, to boot. This would greatly hamper intensification of Alex. However, given that the GFS seems to be the more reliable model with shear profiles, particularly lately, I will go with it and forecast strengthening as Alex emerges into the Bay of Campeche.
How much depends not only track, but on the timing of landfall, as well. I have delayed the system's landfall a bit, in comparison to the NHC, however, and I expect a landfall on late Wednesday night. This forecast will have to be adjusted accordingly as we witness the evolution and progression of the upper trough. So the later Alex comes in, the greater chance it will have to intensify.
Also of note is the TCHP, which, as per the graph above, is quite high across the western Gulf of Mexico, certainly enough to generate a Category 2 hurricane, provided upper-level conditions allow, of course. Should Alex move farther north than forecast, it will have a chance to intensify more than is currently forecast by me or the NHC. Given the uncertainty, however, I'll only go with a minimal hurricane within 72 hours, and an intensifying Category 1 at landfall, which I expect to occur a bit to the north of Tampico, Mexico.
Friday, June 25, 2010
Tropical weather analysis - June 25, 2010
Began writing at approximately 3:19 PM eastern
Invest 93L
Invest 93L continues to display signs of organization, with visible satellite animations depicting a well-organized system. A recent AMSUB pass indicates a well-defined surface circulation, with some convective banding noted, particularly along the eastern flank of the circulation. This circulation might not be closed, however, as surface observations across northern Honduras indicates a lack of prolonged westerly winds (there was a report of some westerly winds across La Mesa and Puerto Cortez at around 8 AM central, but that was it -- again, no prolonged reports of westerly winds). An earlier ship report from the vessel Celebrity Solstice indicated a west wind just offshore the northern coast of Honduras, but has since veered around to the southeast. If there exists a closed surface circulation with this system, it's not a particularly well-defined one yet. An air force reserve hurricane hunter aircraft is currently investigating this system. In any case, I have the center, based on visible imagery and the aforementioned AMSUB pass, at 16N 83W.
Heavy rainfall is likely across portions of Honduras, Nicaragua, Belize, the Yucatan Peninsula, and western Cuba over the next couple of days. I would imagine that these rains could bring some flash flooding and mudslides to Honduras and Nicaragua, given their notorious vulnerability to heavy rains. CIMSS analysis depicts moderate northeasterly shear impinging upon the system.
The culprit of this shear is a well-defined upper-level anticyclone currently centered about 100 miles offshore the northern coast of Honduras. This shear has caused a noticeable elongation of the cloud pattern along the northeastern portion of the circulation.
93L appears, based on satellite animations, to be moving NW at about 5 kt. Recent steering analysis from CIMSS also supports this. This slow movement will allow for 93L to continue gradually deepening, though do place emphasis on the word "gradually" in this case, as there isn't a whole lot of low-level convergence associated with this system, and the system isn't vertically stacked, and the associated vorticity is still elongated. It is best noted at 850 mb, however, and I think this is the most relevant part for now, as the vorticity has improved markedly in this area over the last six hours, a sign of a deepening system. I expect, based on 12z steering currents from PSU, that the current NW motion will continue, eventually increasing to around 10 kt.
This should bring the system into the eastern Yucatan Peninsula by around 36 to 42 hours. Most of the model guidance also reflects this likelihood. As the system enters the western Gulf of Mexico in about 72 hours, there are some indications within the models that the steering flow will collapse for around 24-30 hours, likely due in part to the potent upper-level trough that should ultimately recurve this system toward the northern Gulf Coast (the possibility exists that the trough bypasses the system and 93L instead moves more westward, making landfall somewhere in Mexico or southern and central Texas, but I do not forecast this for now), and a binary interaction between 93L and Eastern Pacific Hurricane Darby. The deeper 93L becomes, the further east Darby will move near the end of the forecast period, and thus, the greater the interaction between the two systems.
By sometime on day four, the models restrengthen the steering currents, though I would imagine that this would occur late on day four, given the possibility of the aforementioned interaction with Darby. At this point, the models do not have a good handle on this system, with some of the models even initializing this system properly. The only models that appear to have properly initialized the system are the GFDL, HWRF, UKMET, and ECMWF. Right now, the majority of the guidance aims the system toward the Mexico or Texas coast in about five days. Based on the fact that I still see this system becoming a relatively deep one, I feel that these models are too far west.
Nevertheless, the current consensus, particularly since the reliable ECMWF is a part of it, cannot be completely ignored (though this consensus is probably due in part to lack of reconnaissance data, which will be fed into these models later, providing us with better and more accurate data). Since I do not want to lean too heavily against the model consensus, I will average the consensus and the outliers (GFDL and HWRF) and forecast a landfall along the Texas/Louisiana border, though this could occur a bit further east, to the west of Vermilion Bay.
However, there is greater than normal uncertainty in this forecast the present time, and residents from Mexico to Florida, particularly from Corpus Christi to Vermilion Bay, should carefully monitor the progress of this system over the next several days.
Upper-level winds appear conducive for at least some slow additional development of this system for the next 18 to 24 hours. Thereafter, 93L could catch up to the anticyclone, which may effectively stall offshore the Yucatan Peninsula during this time. This could provide the system with an environment conducive enough to attain winds of 45 kt before moving inland along the eastern Yucatan Peninsula in 36 hours. There is a possibility, assuming both how strong the system is at landfall here, and how slow it moves after going inland, that the system could decouple across the Yucatan Peninsula, with the low-level center continuing westward, and the mid-level center advecting northeastward in advance of the aforementioned upper-level trough. I do not expect this to happen at the moment, as the forward speed should increase to around 10 kt before and after landfall, but this possibility will be very carefully monitored nonetheless.
After the system enters the western Gulf of Mexico in about 72 hours, upper-level winds should be at least marginally conducive for some additional development, though this is uncertain, given that two very reliable models, the GFS and the ECMWF, foresee two exact opposite scenarios with regards to the vertical shear profiles across the Gulf, with the former showing an anticyclone environment and associated meridional flow, while the latter indicates a largely zonal flow across the Gulf.
It is difficult to tell which is right at this point, so I will average the forecast out. However, it will take 93L at least 24 hours to reinvigorate its circulation after passage over the Yucatan Peninsula, so one should not expect too much intensification of the system as it enters the Gulf. However, conditions appear favorable enough to see a minimal hurricane. There are some indications, even within the GFS, that westerly to southwesterly shear could increase near the coast before landfall, which could act to weaken the system a bit before landfall.
Invest 94L
A well-defined tropical wave was designated Invest 94L by the National Hurricane Center today. Visible satellite animations suggest a strongly sheared system, with most of the associated convection streaming northeastward, away from the surface center. This system is currently undergoing around 30 kt of southwesterly shear, as per CIMSS analysis. This shear is associated with the subtropical jet. The system, expectantly, is not at all aligned in the vertical, with the low- and mid-level centers displaced at least 50 miles to the northeast, due to the aforementioned vertical shear.
Based on 850 mb vorticity data from University of Wisconsin CIMSS, along with visible satellite animations and a recent AMSUB pass, I place the broad surface center at 20N 59W. We have had no recent ASCAT passes over the broad center, but recent ship reports indicate that the center is certainly not closed. Animation of water vapor imagery indicates that a weak upper-level low is centered near 24N 63W. This upper low has broken off from the subtropical jet, and is responsible at least in part for the shear that 94L is currently experiencing. This is a very similar situation, minus the subtropical jet, that occurred with 2008's Hurricane Hanna. Hanna also formed in a similar location to 94L.
Based on visible imagery and CIMSS steering maps, 94L is currently moving NW at about 15 to 20 kt. This fast motion, along with the shear, will make development impossible in the near-term. The models suggest that this swift forward speed should generally continue throughout the forecast period. Indeed, the system might be well-embedded within the westerlies by 108 to 120 hours. However, the upper flow pattern is forecast to improve within about 24 hours as the aforementioned upper low retrogrades westward.
This more favorable pattern aloft should persist until at least 96 hours, when some southwesterly shear could again impinge upon the system. All in all, I expect that this system could eventually develop into a tropical depression, and I give this a 40% chance of happening within the next few days. The NHC foresees a 20% chance of development within the next 48 hours, which is reasonable.
Anything that forms here will only pose a threat to Bermuda, as steering forecasts suggest that the subtropical ridge will weaken further, and the system could turn N by 72 hours. None of the computer models, save the CMC, develops this system, though the GFS is hinting at development.
Invest 93L
Invest 93L continues to display signs of organization, with visible satellite animations depicting a well-organized system. A recent AMSUB pass indicates a well-defined surface circulation, with some convective banding noted, particularly along the eastern flank of the circulation. This circulation might not be closed, however, as surface observations across northern Honduras indicates a lack of prolonged westerly winds (there was a report of some westerly winds across La Mesa and Puerto Cortez at around 8 AM central, but that was it -- again, no prolonged reports of westerly winds). An earlier ship report from the vessel Celebrity Solstice indicated a west wind just offshore the northern coast of Honduras, but has since veered around to the southeast. If there exists a closed surface circulation with this system, it's not a particularly well-defined one yet. An air force reserve hurricane hunter aircraft is currently investigating this system. In any case, I have the center, based on visible imagery and the aforementioned AMSUB pass, at 16N 83W.
Heavy rainfall is likely across portions of Honduras, Nicaragua, Belize, the Yucatan Peninsula, and western Cuba over the next couple of days. I would imagine that these rains could bring some flash flooding and mudslides to Honduras and Nicaragua, given their notorious vulnerability to heavy rains. CIMSS analysis depicts moderate northeasterly shear impinging upon the system.
The culprit of this shear is a well-defined upper-level anticyclone currently centered about 100 miles offshore the northern coast of Honduras. This shear has caused a noticeable elongation of the cloud pattern along the northeastern portion of the circulation.
93L appears, based on satellite animations, to be moving NW at about 5 kt. Recent steering analysis from CIMSS also supports this. This slow movement will allow for 93L to continue gradually deepening, though do place emphasis on the word "gradually" in this case, as there isn't a whole lot of low-level convergence associated with this system, and the system isn't vertically stacked, and the associated vorticity is still elongated. It is best noted at 850 mb, however, and I think this is the most relevant part for now, as the vorticity has improved markedly in this area over the last six hours, a sign of a deepening system. I expect, based on 12z steering currents from PSU, that the current NW motion will continue, eventually increasing to around 10 kt.
This should bring the system into the eastern Yucatan Peninsula by around 36 to 42 hours. Most of the model guidance also reflects this likelihood. As the system enters the western Gulf of Mexico in about 72 hours, there are some indications within the models that the steering flow will collapse for around 24-30 hours, likely due in part to the potent upper-level trough that should ultimately recurve this system toward the northern Gulf Coast (the possibility exists that the trough bypasses the system and 93L instead moves more westward, making landfall somewhere in Mexico or southern and central Texas, but I do not forecast this for now), and a binary interaction between 93L and Eastern Pacific Hurricane Darby. The deeper 93L becomes, the further east Darby will move near the end of the forecast period, and thus, the greater the interaction between the two systems.
By sometime on day four, the models restrengthen the steering currents, though I would imagine that this would occur late on day four, given the possibility of the aforementioned interaction with Darby. At this point, the models do not have a good handle on this system, with some of the models even initializing this system properly. The only models that appear to have properly initialized the system are the GFDL, HWRF, UKMET, and ECMWF. Right now, the majority of the guidance aims the system toward the Mexico or Texas coast in about five days. Based on the fact that I still see this system becoming a relatively deep one, I feel that these models are too far west.
Nevertheless, the current consensus, particularly since the reliable ECMWF is a part of it, cannot be completely ignored (though this consensus is probably due in part to lack of reconnaissance data, which will be fed into these models later, providing us with better and more accurate data). Since I do not want to lean too heavily against the model consensus, I will average the consensus and the outliers (GFDL and HWRF) and forecast a landfall along the Texas/Louisiana border, though this could occur a bit further east, to the west of Vermilion Bay.
However, there is greater than normal uncertainty in this forecast the present time, and residents from Mexico to Florida, particularly from Corpus Christi to Vermilion Bay, should carefully monitor the progress of this system over the next several days.
Upper-level winds appear conducive for at least some slow additional development of this system for the next 18 to 24 hours. Thereafter, 93L could catch up to the anticyclone, which may effectively stall offshore the Yucatan Peninsula during this time. This could provide the system with an environment conducive enough to attain winds of 45 kt before moving inland along the eastern Yucatan Peninsula in 36 hours. There is a possibility, assuming both how strong the system is at landfall here, and how slow it moves after going inland, that the system could decouple across the Yucatan Peninsula, with the low-level center continuing westward, and the mid-level center advecting northeastward in advance of the aforementioned upper-level trough. I do not expect this to happen at the moment, as the forward speed should increase to around 10 kt before and after landfall, but this possibility will be very carefully monitored nonetheless.
After the system enters the western Gulf of Mexico in about 72 hours, upper-level winds should be at least marginally conducive for some additional development, though this is uncertain, given that two very reliable models, the GFS and the ECMWF, foresee two exact opposite scenarios with regards to the vertical shear profiles across the Gulf, with the former showing an anticyclone environment and associated meridional flow, while the latter indicates a largely zonal flow across the Gulf.
It is difficult to tell which is right at this point, so I will average the forecast out. However, it will take 93L at least 24 hours to reinvigorate its circulation after passage over the Yucatan Peninsula, so one should not expect too much intensification of the system as it enters the Gulf. However, conditions appear favorable enough to see a minimal hurricane. There are some indications, even within the GFS, that westerly to southwesterly shear could increase near the coast before landfall, which could act to weaken the system a bit before landfall.
Invest 94L
A well-defined tropical wave was designated Invest 94L by the National Hurricane Center today. Visible satellite animations suggest a strongly sheared system, with most of the associated convection streaming northeastward, away from the surface center. This system is currently undergoing around 30 kt of southwesterly shear, as per CIMSS analysis. This shear is associated with the subtropical jet. The system, expectantly, is not at all aligned in the vertical, with the low- and mid-level centers displaced at least 50 miles to the northeast, due to the aforementioned vertical shear.
Based on 850 mb vorticity data from University of Wisconsin CIMSS, along with visible satellite animations and a recent AMSUB pass, I place the broad surface center at 20N 59W. We have had no recent ASCAT passes over the broad center, but recent ship reports indicate that the center is certainly not closed. Animation of water vapor imagery indicates that a weak upper-level low is centered near 24N 63W. This upper low has broken off from the subtropical jet, and is responsible at least in part for the shear that 94L is currently experiencing. This is a very similar situation, minus the subtropical jet, that occurred with 2008's Hurricane Hanna. Hanna also formed in a similar location to 94L.
Based on visible imagery and CIMSS steering maps, 94L is currently moving NW at about 15 to 20 kt. This fast motion, along with the shear, will make development impossible in the near-term. The models suggest that this swift forward speed should generally continue throughout the forecast period. Indeed, the system might be well-embedded within the westerlies by 108 to 120 hours. However, the upper flow pattern is forecast to improve within about 24 hours as the aforementioned upper low retrogrades westward.
This more favorable pattern aloft should persist until at least 96 hours, when some southwesterly shear could again impinge upon the system. All in all, I expect that this system could eventually develop into a tropical depression, and I give this a 40% chance of happening within the next few days. The NHC foresees a 20% chance of development within the next 48 hours, which is reasonable.
Anything that forms here will only pose a threat to Bermuda, as steering forecasts suggest that the subtropical ridge will weaken further, and the system could turn N by 72 hours. None of the computer models, save the CMC, develops this system, though the GFS is hinting at development.
Thursday, June 24, 2010
Tropical weather analysis - June 24, 2010
Began writing at approximately 8:58 PM eastern
Invest 93L has become much better organized this evening. Infrared satellite loops indicate that convection, while not quite as cold as it was earlier, continues to expand. The improving surface center appears to be centered along the extreme northern edge of the deep convection, as per various satellite animations. I place the center at 16N 80W. CIMSS analysis depicts about 20 kt of northwesterly shear impinging over the system, emanating from the eastern extent of a well-defined upper-level anticyclone currently centered several hundred miles east of Honduras. This likely explains the fact that the center is not fully embedded within the deep convection.
Water vapor loops show that any dry air currently present to the west of the system is quickly mixing out, and I am not expecting dry air to be a problem for 93L in the near-term. Low-level convergence and upper-level divergence associated with the system are currently rather meager. This, along with the moderate northwesterly shear that the system is currently experiencing, should limit any rapid development in the near-term, though I do expect a gradual consolidation of the system for the next 12 hours. The GFS suggests that the anticyclone will move northward toward the Yucatan Channel beginning in about 18 to 24 hours.
By this time, 93L should be nearing that area, and so should this forecast transpire, 93L will have ample opportunity to develop into a tropical depression tomorrow. A reconnaissance aircraft is scheduled to investigate the system tomorrow, if necessary. The previous two flights have been canceled due to a lack of organization, but if current trends continue, I suspect that tomorrow's flight will be allowed to commence. This should provide us with valuable data that will allow the models, which have been doing rather poorly with this system -- what with the flip flopping and all, to initialize the system better, and hopefully more accurately predict both track and intensity.
There is currently a belt of very high wind shear, 40 knots in some areas, across the southern and central Gulf of Mexico. Both the GFS and ECMWF, our two most reliable models, foresee this shear lifting out as 93L enters the Gulf of Mexico in around 72 hours. Should this indeed happen, it would allow the system to intensify up until landfall along the western or northern Gulf Coast in about 132 hours. It should be noted, however, that the GFS no longer foresees an anticyclonic environment across the Gulf of Mexico, at least after the first day or so that the system enters the Gulf. This would allow 93L to be highly vulnerable to any vertical shear. We will see how this goes.
Right now, conditions appear favorable enough for a tropical depression to form within the next 24 to 36 hours, and then eventually to a minimal hurricane as the system traverses the central Gulf of Mexico. Curiously, the ECMWF is rather slow with this system, delaying the time of landfall along the Gulf Coast full 24 hours in comparison to the other models. It could be picking up on a possible collapse of steering currents in about three to four days as the system traverses the Gulf of Mexico. Out of respect for this possible scenario, as well as the fact that the ECMWF is a rather well-performing model, I will forecast a landfall along the northern Gulf Coast in 132 hours.
It also doesn't show a landfall along the Yucatan Peninsula until 72 hours, while the other models show 48 hours. I will once again split the difference here and forecast a landfall along the eastern Yucatan Peninsula in around 48 hours. After landfall in the Yucatan Peninsula, the system should enter the southern Gulf of Mexico by around 72 hours, at which point a strong upper-level trough approaching from the west will begin moving the system more poleward. Right now, I don't think any of the models have a particularly good handle on the eventual track of this system, though I suspect that 93L will make landfall somewhere along the western or central Louisiana coast in five days.
However, this is far from certain, especially pending recon data, so residents all along the Gulf of Mexico, particularly from Galveston to Pensacola, should carefully monitor the progress of this system over the next several days.
Interestingly, the 18z GFDL and HWRF do not make the system a tropical cyclone throughout the forecast period, and instead bring it to the northern Gulf Coast as a sheared system with 25 kt winds. This is considered highly unrealistic for now, in light of what was said above.
Invest 93L has become much better organized this evening. Infrared satellite loops indicate that convection, while not quite as cold as it was earlier, continues to expand. The improving surface center appears to be centered along the extreme northern edge of the deep convection, as per various satellite animations. I place the center at 16N 80W. CIMSS analysis depicts about 20 kt of northwesterly shear impinging over the system, emanating from the eastern extent of a well-defined upper-level anticyclone currently centered several hundred miles east of Honduras. This likely explains the fact that the center is not fully embedded within the deep convection.
Water vapor loops show that any dry air currently present to the west of the system is quickly mixing out, and I am not expecting dry air to be a problem for 93L in the near-term. Low-level convergence and upper-level divergence associated with the system are currently rather meager. This, along with the moderate northwesterly shear that the system is currently experiencing, should limit any rapid development in the near-term, though I do expect a gradual consolidation of the system for the next 12 hours. The GFS suggests that the anticyclone will move northward toward the Yucatan Channel beginning in about 18 to 24 hours.
By this time, 93L should be nearing that area, and so should this forecast transpire, 93L will have ample opportunity to develop into a tropical depression tomorrow. A reconnaissance aircraft is scheduled to investigate the system tomorrow, if necessary. The previous two flights have been canceled due to a lack of organization, but if current trends continue, I suspect that tomorrow's flight will be allowed to commence. This should provide us with valuable data that will allow the models, which have been doing rather poorly with this system -- what with the flip flopping and all, to initialize the system better, and hopefully more accurately predict both track and intensity.
There is currently a belt of very high wind shear, 40 knots in some areas, across the southern and central Gulf of Mexico. Both the GFS and ECMWF, our two most reliable models, foresee this shear lifting out as 93L enters the Gulf of Mexico in around 72 hours. Should this indeed happen, it would allow the system to intensify up until landfall along the western or northern Gulf Coast in about 132 hours. It should be noted, however, that the GFS no longer foresees an anticyclonic environment across the Gulf of Mexico, at least after the first day or so that the system enters the Gulf. This would allow 93L to be highly vulnerable to any vertical shear. We will see how this goes.
Right now, conditions appear favorable enough for a tropical depression to form within the next 24 to 36 hours, and then eventually to a minimal hurricane as the system traverses the central Gulf of Mexico. Curiously, the ECMWF is rather slow with this system, delaying the time of landfall along the Gulf Coast full 24 hours in comparison to the other models. It could be picking up on a possible collapse of steering currents in about three to four days as the system traverses the Gulf of Mexico. Out of respect for this possible scenario, as well as the fact that the ECMWF is a rather well-performing model, I will forecast a landfall along the northern Gulf Coast in 132 hours.
It also doesn't show a landfall along the Yucatan Peninsula until 72 hours, while the other models show 48 hours. I will once again split the difference here and forecast a landfall along the eastern Yucatan Peninsula in around 48 hours. After landfall in the Yucatan Peninsula, the system should enter the southern Gulf of Mexico by around 72 hours, at which point a strong upper-level trough approaching from the west will begin moving the system more poleward. Right now, I don't think any of the models have a particularly good handle on the eventual track of this system, though I suspect that 93L will make landfall somewhere along the western or central Louisiana coast in five days.
However, this is far from certain, especially pending recon data, so residents all along the Gulf of Mexico, particularly from Galveston to Pensacola, should carefully monitor the progress of this system over the next several days.
Interestingly, the 18z GFDL and HWRF do not make the system a tropical cyclone throughout the forecast period, and instead bring it to the northern Gulf Coast as a sheared system with 25 kt winds. This is considered highly unrealistic for now, in light of what was said above.
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