KoritheMan's WunderBlog

Tropical weather analysis - June 30, 2010

By: KoritheMan, 1:13 AM GMT on July 01, 2010

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.



Figure 1. Latest infrared satellite image of Hurricane Alex. Notice the small eye just offshore the northeastern Mexico coast.

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.



Figure 2. List of severe weather reports so far today, as per the Storm Prediction Center in Norman, Oklahoma. Notice the tornado reports so far today in the state of Texas. There could be some additional reports of tornadoes before all is said and done.

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.

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Tropical weather analysis - June 29, 2010

By: KoritheMan, 1:14 AM GMT on June 30, 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.



Figure 1. Latest infrared satellite image of Tropical Storm Alex.

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.



Figure 2. Tropical Cyclone Heat Potential (TCHP) in the Gulf of Mexico. Values 80 or greater are considered conducive to rapid intensification.

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.

Updated: 1:19 AM GMT on June 30, 2010

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Tropical weather analysis - June 28, 2010

By: KoritheMan, 2:02 AM GMT on June 29, 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.



Figure 1. Latest infrared satellite image of Tropical Storm Alex.

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.



Figure 2. Gulf of Mexico Sea Surface Temperatures (SSTs), as per June 27, 2010. During this time, SSTs at 20N 90W, the current estimate for Alex's center, were a warm 28C, more than sufficient to intensify the system. However, keep in mind that this map is from yesterday, and we won't be getting today's version until tomorrow. Hence, these waters may only be at 26C now, due to how long Alex has been meandering in the area.

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.



Figure 3. Tropical Cyclone Heat Potential (TCHP) across the Gulf of Mexico as of June 27, 2010. Values of 80 and above is considered the threshold for rapid intensification.

As you can see from the graph above, 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.

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Tropical weather analysis - June 27, 2010 - second edition

By: KoritheMan, 12:50 AM GMT on June 28, 2010

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.

Updated: 12:57 AM GMT on June 28, 2010

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Tropical weather analysis - June 27, 2010

By: KoritheMan, 5:21 AM GMT on 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.



Figure 1. Latest infrared satellite loop of Tropical Storm Alex.

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.



Figure 2. Current Tropical Cyclone Heat Potential (TCHP) across the Gulf of Mexico. Typically, values of 80 or higher tend to support rapid intensification of a tropical cyclone.

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.

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Tropical weather analysis - June 25, 2010

By: KoritheMan, 9:33 PM GMT on 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.



Figure 1. Latest visible satellite image of Invest 93L.

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.

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Tropical weather analysis - June 24, 2010

By: KoritheMan, 1:52 AM GMT on June 25, 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.



Figure 1. Latest infrared satellite image of Invest 93L.

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 60 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.

Updated: 2:03 AM GMT on June 25, 2010

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Tropical weather analysis - June 23, 2010

By: KoritheMan, 12:20 AM GMT on June 24, 2010

Began writing at approximately 7:30 PM eastern

Invest 93L continues to struggle. This was not totally unexpected, however, as I had predicted last night that this would happen throughout a portion of today. The last of the visible satellite animations suggest that the broad and poorly defined surface center -- if it can even be accurately referred to as such -- is located at 18N 79W. There also appears to be several other vorticity maximums embedded within the broad cyclonic gyre associated with this system. It appears that the anticyclone, which was practically atop 93L last night appears to have shifted a bit westward today, and its axis is now located southwest of Jamaica. This appears to be producing 20 kt of westerly shear across the estimated center position. This would at least partially explain 93L's current disorganization, as satellite loops show that the system's associated convection is not well organized, and is instead displaced to the east of the estimated "surface center".



Figure 1. Latest infrared satellite image of Invest 93L. Notice the disorganized appearance I alluded to earlier, with a large area of showers and thunderstorms covering the western and central Caribbean.

The biggest change I have noted with 93L today is pressure falls, with several land stations, and even one oceanic station, "Station 42057", reporting significant pressure falls. Surface pressures are rising to the east, within the convective mass affecting Hispaniola, indicating that 93L's competing influence may finally be starting to gradually dissipate. Should this indeed be occurring, it should finally allow 93L to "breathe", so to speak. However, I do suspect that any development will be slow to occur with 93L, and we will not see tropical cyclogenesis until tomorrow night at the very earliest. 93L is currently moving W at 10 to 15 kt. I expect oscillations between W and WNW over the next day or so. At that point, 93L could either not strengthen significantly, if at all, and head W into the Yucatan Peninsula and dissipate, or it could strengthen and continue WNW into the southern Gulf of Mexico, following the mid-level atmospheric flow. It continues to be very difficult to accurately predict this system, and given recent model trends calling for a much weaker storm or even dissipation, I am also going to be less bullish than I was this time yesterday. However, I do still expect this system to be deep enough to follow the mid-level flow and eventually move across the southern and central Gulf of Mexico.

The eventual landfall location of this system in the Gulf of Mexico, assuming it makes it there, is highly uncertain. Texas does appear to be at greater risk than it was this time yesterday, simply because the system is being slow to organize. Residents from Mexico to Florida, with emphasis along the entire Texas coast and much of the Louisiana coast, should carefully monitor the progress of this system over the next several days. The GFS abates the current westerly shear in about 18 hours, giving way to more favorable northerlies. It also stalls the anticyclone in the Yucatan Channel from 36 to 84 hours. This is critical, because 93L might be able to catch up with the anticyclone and establish itself underneath it during this time, which would greatly assist in development. Even if it doesn't, the flow along the eastern periphery of the anticyclone will be N, NE, and then it will veer to the E. This upper flow pattern is much more conducive to intensification than the currently westerly flow aloft, which is also being generated by the aforementioned anticyclone.

Bottom line is, conditions appear conducive for steady development as the system enters the western Caribbean in about 18 hours. The GFS suggests that the westerly shear I mentioned last night, that was supposed to be blowing across the central and northern Gulf of Mexico, won't be present throughout the forecast period. Should this hold true, and 93L remain intact long enough to reach the Gulf of Mexico, we need to keep a very watchful eye on this situation.

I do not foresee this system becoming a major hurricane at this point, or even a Category 2. I expect, if it holds together, a Category 1 hurricane, but not until it reaches the central Gulf of Mexico.

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Tropical weather analysis - June 22, 2010

By: KoritheMan, 1:33 AM GMT on June 23, 2010

Began writing approximately 8:26 PM eastern

Invest 93L continues to thrive, and is generating heavy thunderstorms over portions of Puerto Rico, Hispaniola, Jamaica, and eastern Cuba. These heavy rains may cause some flash flooding and mudslides across earthquake-ravaged Haiti over the next day or two, as I would imagine that 3-6 inches of rain is likely to fall there, with locally higher amounts, particularly across mountainous regions. Based upon shortwave infrared satellite loops, it appears that the center is located near 16N 75W. Deep convection is currently minimal near the estimated center position, but appears to be acquiring banding features, with the thunderstorms attempting to wrap cyclonically into the broad but gradually organizing surface center.



Figure 1. Latest infrared satellite image of Invest 93L. Note the disorganized appearance of the storm at present. Also, that massive thunderstorm complex drenching portions of Hispaniola and Puerto Rico does not have a surface reflection, much less any 850 mb vorticity.

93L is currently centered almost completely underneath an upper-level anticyclone. This, along with strong vertical shear from the TUTT to the north, should assist in ventilation of the system. However, given that divergence convergence are naturally stronger during persistent convection, ala the aforementioned thunderstorm complex to the east of 93L's estimated center, it is my prediction that 93L will struggle a little bit this evening, as that thunderstorm complex robs it of most of its energy. Think of it like a developing tropical cyclone in the ITCZ -- often times they compete with one another, and ultimately, one of them wins out. So who will win out in this particular situation? I would say 93L, given that an anticyclone is centered above the system. However, given the aforementioned influence, along with surface and buoy observations indicating a lack of a closed surface circulation, I am not expecting any significant development of 93L tonight, and even into this morning. By tomorrow afternoon, however, it should begin to organize. A reconnaissance flight is scheduled for 93L tomorrow, and they will no doubt be able to provide us with better data than what we currently have, should the mission actually transpire.

93L is currently moving W at 5-10 kt, based on satellite animations and low- to mid-level steering analysis from CIMSS. I expect a general WNW motion, with the occasional jog to the W at around 5-10 kt throughout the next several days, and I do expect that 93L will eventually find its way into the Gulf of Mexico. The models are divided as to whether or not 93L will eventually develop. The CMC, ECMWF, GFDL, and HWRF all foresee the system developing, and all of them save the HWRF bring it to hurricane status while located across the southern Gulf of Mexico. The NOGAPS, GFS, and UKMET models, on the other hand, do not develop 93L (though the GFS is showing the formation of a low pressure area on the verge of becoming a tropical depression, more than it has been doing for the last several days). However, they all agree on one thing: a shortwave trough in the westerlies will begin eroding the subtropical ridge, the western extent of which is currently located east-west across a large portion of the eastern and northern Gulf of Mexico, by around 72 hours. 93L should be either be approaching landfall in the Yucatan Peninsula at this time. the solution provided by the NOGAPS, GFS, and UKMET, or in the Yucatan Channel between the Yucatan Peninsula and western Cuba. The former is more likely in the event of a weaker system following the low-level flow, while the latter is more likely with a vertically deep system following the mid-level flow.

Based on the GFS's consistent forecast (even as per the 18z run) of an the current anticyclone to follow 93L into the Gulf of Mexico, I am more inclined to agree with the latter solution, as I expect this system to strengthen. The models develop a low pressure area around this system around 48 hours, and this seems reasonable. Thereafter, I expect a rapid consolidation of the system, and it should already be a tropical storm, possibly a minimal hurricane as it approaches the Yucatan Channel by 72 hours. Thereafter, the system is likely to begin to move more poleward as it enters the southern Gulf of Mexico, specifically NW, then N, as the aforementioned trough enters the picture and erodes the ridge. The system may pass over a warm eddy currently located across the southern Gulf of Mexico, and should this occur, it could rapidly intensify. The 18z GFDL makes this system a 100 kt (115 mph) major hurricane as it approaches the southeastern Louisiana coast in just a little over five days.

While I will not go that high at this time, I do expect that this system will, at the very least, eventually reach 80 kt (90 mph), and could possibly even attain Category 2 status while in the Gulf of Mexico. It is highly uncertain at this time to pinpoint the eventual landfall location of this system should it indeed enter the Gulf, but I put the area of Galveston to Morgan City at greatest risk. Nevertheless, residents across the entire Gulf of Mexico, particularly the western and northern, should closely monitor the progress of this system over the next several days.

There are some indications that upper-level westerly shear could impinge upon the system as it moves across the central Gulf of Mexico, but the models are in large disagreement on this, with the GFS keeping the anticyclone intact. We shall see, as it is far too early to determine which scenario is more viable.

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Tropical weather analysis - June 21, 2010

By: KoritheMan, 1:29 AM GMT on June 22, 2010

Began writing at approximately 8:25 PM eastern

Almost immediately after persistent 92L dissipated, we have a new invest -- Invest 93L. This system has much more favorable atmospheric conditions with which to develop than 92L ever did, even when it looked to be consolidating in the far eastern tropical Atlantic. According to the last of the visible satellite animations, along with buoy observations, strongly suggest 93L does not appear to have a surface circulation at this time, and certainly not a closed one. CIMSS 850 mb vorticity data does show, however, a small area of more concentrated rotation to the south of eastern Hispaniola. Satellite animations also confirm that there exists some weak rotation within this area. However, I do not believe that this is the surface center, because again, not only do I believe that isn't one yet, it's also because this area of vorticity has been gradually weakening in recent hours. A recent ASCAT pass indicates a sharp wind shift near 16N 70W, though satellite imagery is in conflict with this. Surface pressures are not falling in the vicinity, so no rapid organization will occur tonight and into this morning.



Figure 1. Latest infrared satellite image of Invest 93L. Notice that the system is not well organized at the moment, though it does contain a lot of moisture.

Upper-level shear is only 10 to 15 kt over the system at the moment, and has been steadily decreasing over the last 12 hours. This, along with some decent upper-level divergence, low-level convergence, and finally, a very moist environment, supports continued convective development. Remember though, this system is disorganized at present, with no signs of a surface circulation or falling pressures. Hence, I do not believe that any rapid organization is in order in the near-term (the next 12 to 18 hours). This system is currently moving W at 5-10 kt, and I expect this motion to continue for the next 12 hours or so, after which point a steady WNW movement, with some occasional oscillations to the W, should occur. I base this on the 18z GFDL, which I feel has the most realistic representation of 93L, in terms of depth. A more shallow system, as the CMC, NOGAPS, and GFS are predicting, would tend to follow the low-level flow and move more southerly, which I do not buy at this time, based on current steering analysis from CIMSS, as well as due to the fact that this system should organize quicker than the aforementioned three models are saying.

Alarmingly, the GFS, as per the 18z run, still insists on creating a very favorable environment across the entire Caribbean from now throughout much of the forecast period. In fact, much of this environment could be anticyclonic in nature, and the GFS insists that this anticyclone will begin to develop by just 24 hours. This has consistently been the case on this model for the last two and a half to three days at this point. Given that I find the GFS performs the best with regards to vertical shear, I will be keeping a very close eye on this. It already appears that there is an anticyclone attempting to establish itself across the eastern Caribbean, so this certainly lends some credence to the GFS's forecast. The CMC and NOGAPS are also showing this, though the NOGAPS almost always has a low-shear bias from my observation, so it's probably irrelevant with regards to that particular model.

All in all, the NHC's forecast of a 50% chance of tropical cyclogenesis within the next 48 hours appears to be a reasonable one. The ultimate track of this system is uncertain, and residents from the Yucatan Peninsula throughout the entire Gulf of Mexico should carefully monitor the progress of this system over the next week.

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Tropical weather analysis - June 20, 2010

By: KoritheMan, 3:28 AM GMT on June 21, 2010

Began writing at approximately 10:19 PM eastern

Invest 92L

Invest 92L is no more. Strong upper-level winds, dry air, and land interaction have all but destroyed the system. It appeared very early this morning, as per doppler radar loops from San Juan, Puerto Rico, along with CIMSS vorticity data, that 92L was trying to form a new center underneath the deepest convection, which was located southwest of Ponce at that time. However, this did not materialize. Doppler radar animations out of San Juan still indicate a large amount of moisture in the vicinity. However, this precipitation is more likely associated with a tropical wave currently stretching from northeastern Venezuela northward to the Leeward Islands, rather than 92L. In any case, this moisture is located well to the east of the wave axis of 92L, which is currently devoid of deep convection. There is no organization to these showers, as evidenced by not only doppler radar data, but also infrared satellite loops. There is also very little in the way of low-level vorticity associated with this system, and indeed, 92L's convection (which, again, is displaced well to the east of the very weak wave axis) appears to be becoming increasingly and rapidly influenced by the large area of moisture currently evident across the eastern Caribbean. Given that there is currently no model support at all for 92L, and the fact that most of the models foresee the aforementioned area of moisture, associated with a westward-moving tropical wave, becoming the dominant system, I do not expect any significant development of 92L.



Figure 1. Current infrared satellite image of the Caribbean Sea. As you can see, there is a large area of disorganized moisture, associated in part with the remnant convection of 92L, but more in part by the aforementioned tropical wave.

The wave (92L's wave), as per the 1800 UTC NHC surface analysis map, currently extends along 22N 73W to 11N 75W, and is moving W near 15 kt, embedded within the low-level easterlies, the signature of the tropics. Based on water vapor animations, 12z steering from PSU, and the current low-level steering wind flow, as per University of Wisconsin CIMSS, I expect 92L continue to moving W at around 10 to 15 kt for the next 12 to 18 hours, after which a WNW movement should begin, across western or central Cuba. 92L still appears quite poised to enter the Gulf of Mexico, but at this point, it appears that 92L's structure is much too disrupted to ever reinvigorate. Indeed, I have been giving this system only a low chance, 20%, to ultimately develop into a tropical depression in the Gulf of Mexico, but given recent structural trends, I will have to lower that probability to only 5%. At this point, it does not appear likely that 92L will pose a significant threat to any land areas as a tropical cyclone, though it may produce occasional locally heavy rainfall across portions of western and central Cuba, the northern Yucatan Peninsula, and eventually, portions of northeastern Mexico and southern and central Texas over the next several days.

Unless conditions significantly change, this will be my final mention of 92L. It was a tenacious system, to be sure.

Windward Islands tropical wave

The aforementioned tropical wave is the one we really need to keep a watchful eye on. This system might ultimately entrain some moisture from an area of disturbed weather currently located near Nicaragua, as well as from another tropical wave currently along 45W. The 12z NOGAPS, the 12z ECMWF, and the 12z CMC were all developing this wave, and had it in the Yucatan Channel at 144 hours. The NOGAPS and ECMWF had it between western Cuba and the Yucatan Peninsula at this time, while the CMC tracked it westward across the Yucatan Peninsula, and then into the Gulf of Mexico. The 18z GFS predicts a largely anticyclonic environment across much of the Caribbean beginning in about 72 hours, and eventually brings this favorable environment into much of the Gulf of Mexico, where this potential system appears likely to eventually end up. Residents from Mexico to Florida should carefully monitor the progress of this wave over the next several days. It should be noted that the ECMWF has been consistent in making this system a hurricane in the Gulf of Mexico, though this is highly uncertain at this time.

The most useful forecast I can give for this system at the moment is that it has a far greater chance to develop than 92L ever did. The NHC is currently giving this system a 10% chance of becoming a tropical cyclone in the next 48 hours, due to moderate westerly shear, and this is a reasonable forecast. This shear should let up by around 72 hours, at which point we will need to monitor this system for potential tropical development. In the meantime, expect this system to oscillate between W and WNW at around 10 to 15 kt over the next several days, though the direction should be mostly WNW.

Updated: 3:33 AM GMT on June 21, 2010

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Tropical weather analysis - June 19, 2010

By: KoritheMan, 12:49 AM GMT on June 20, 2010

Began writing at approximately 7:31 eastern

Invest 92L continues to stubbornly generate deep convection, in spite of hostile upper-level winds, analyzed at 20 kt per University of Wisconsin's CIMSS. Based upon recent buoy observations, surface observations from Puerto Rico, doppler radar animation from San Juan, along with shortwave infrared satellite loops, I have fixed a center at 17N 67W.



Figure 1. Latest infrared satellite image of Invest 92L, courtesy of NOAA.

92L has finally been able to generate some convection near the center this evening, probably because the shear is only 20 kt, compared to the much more oppressive 30 to 50 kt shear it has been dealing with over the last several days. However, animation of water vapor imagery indicates that dry air lies just to the west of the system, and will continue to be ingested into the system thanks to the aforementioned upper-level westerlies. Interestingly, in a sharp contrast compared to recent days, 92L's vorticity only extends upward to 700 mb. This further suggests that, in spite of convection finally being closer to the center this evening, 92L will not organize into a tropical depression in the near-term. The main impact from this system in the near-term will be continued locally heavy rains across portions of the northern Leeward Islands, the Virgin Islands, Puerto Rico (particularly the southern half), and across Hispaniola. Already, doppler radar estimates from San Juan indicate a large swath of 2 to 4 inches of rain from the southwestern end of the island eastward, with some localized amounts in excess of 5 to 6 inches. I would expect an additional 1 to 2 inches across these areas, with locally higher amounts possible across mountainous areas.

92L is currently moving W based on satellite animations. I expect this general motion to continue for about the next 12 hours or so, after which point a steady WNW movement should continue, even as the system moves into the southern or southeastern Gulf of Mexico by day four. At this point, the models sharply diverge, with the CMC being farthest south, taking the system westward into the Yucatan Peninsula by day four. It's very difficult to pinpoint this far out just which portion of the Gulf Coast ultimately gets affected by this system. I know I normally forecast a definite path for an invest throughout the forecast period, but the uncertainty is much too great at this point to do that. If I was forced to do so though, I would say the western Gulf Coast is most at risk from this system. However, this is highly uncertain.

The models do agree on one thing, however, and that's the fact that 92L will make landfall across southwestern Hispaniola in about 24 to 30 hours. Afterward, I expect a continued WNW motion toward the western Caribbean to south of central Cuba. At this point in the period is around to 60 to 72 hours. Upper-level shear should still be unfavorable at this point, but will be gradually lessening. More importantly, 92L will be traversing across some of the hottest water in the basin. These waters extend to great depth, and are easily enough to generate a major hurricane. Not that I expect 92L to achieve that feat, of course. Far from it, in fact. These warm waters, combined with the lowering (but still prohibitive) vertical shear, should allow the system to generate vigorous convection, and a flash flood event is possible across portions of Cuba during this time, particularly across mountainous areas.



Figure 2. Tropical Cyclone Heat Potential (TCHP) across the Caribbean as of June 18, 2010. TCHP values above 80 is considered very beneficial for rapid intensification.

When 92L enters the Gulf in four days, shear should be favorable enough to allow steady intensification of 92L, assuming that its structure is not too disrupted by passage across Hispaniola and Cuba. I will continue to give 92L a 20% chance of eventually developing into a tropical cyclone in the Gulf of Mexico, though this will need to be increased if its structure remains intact after passage across the islands, or if it misses them altogether.

Elsewhere

Elsewhere in the tropics, the NOGAPS is developing a tropical depression in the central Caribbean Sea by late next week. Upper-level winds will be near zero in this region, so we need to monitor this very carefully, should this transpire. Given the timeframe, it is possible that this system originates from the tropical wave I've been mentioning that was forecast to move across the Windward Islands in less than a week. None of the other models are developing this area, but the GFS indicates a large area of concentrated moisture across that region, so we should carefully watch this, as the potential for mischief is certainly there.

There is also a rather nice looking low pressure system currently just to the north of Panama. Steering currents are weak in this area at the moment, but the models foresee a slow westward drift into Central America. However, there is a well-defined anticyclone centered over this system in the upper-levels, so should this system deviate from the current westward projection, it will need to be carefully monitored for the potential formation of a tropical depression. Locally heavy rainfall, particularly across mountainous areas, will be possible across portions of Panama, Costa Rica, Nicaragua, and Honduras over the next couple of days.

Updated: 1:05 AM GMT on June 20, 2010

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Tropical weather analysis - June 18, 2010

By: KoritheMan, 11:50 PM GMT on June 18, 2010

Began writing at approximately 6:20 PM EDT

Invest 92L continues to thrive, generating persistent but highly disorganized convection. Most of the convection is displaced well to the east of the center at the moment, owing to strong upper-level westerly shear, analyzed at 30 kt by the University of Wisconsin's CIMSS.



Figure 1. Latest infrared satellite image of Invest 92L, courtesy of NOAA.

Based upon analysis of the last visible satellite animations of the day, along with recent buoy observations and recent microwave imagery, courtesy of the Navy Research Lab (NRL), I estimate that the center is located near 17N 64W, along the extreme western edge of the disorganized convection in that vicinity. This isn't certain, however, given the system's current disorganization. These same observations, along with surface observations from the Leeward Islands, U.S. and British Virgin Islands, indicate that there are no signs of a circulation at this time. As for movement, it appears to me, based on satellite animations along with doppler radar animations from Martinique, that 92L is moving due W. A rather meager thermodynamic environment continues to plague 92L, as animation of water vapor imagery indicates dry air encroaching upon the system from the west and southwest, owing to the aforementioned vertical shear, though the dry air does appear to be lessening some -- gradually.

However, that, along with an almost complete lack of upper-level divergence near the estimated center, should prohibit the development of organized deep convection near the center, at least for the next several hours. As the environment continues to gradually moisten, however, and divergence increases, we might see another brief bout of deep convection that persists for several hours. Should this predicted flareup occur as it has for the last several nights, it could generate some rather heavy rainfall across Puerto Rico tonight and into this morning, particularly along the southern coastline. Orographic lift will also act to contribute to heavier rainfall across the mountainous portions of that island. I do not expect a serious flash flood disaster, however. Notwithstanding, Puerto Rico, along with the Leeward Islands, U.S. and British Virgin Islands, could continue to see some locally heavy rainfall, along with wind gusts in excess of 30 to 35 kt. Given that vertical shear has been steadily decreasing in the path of 92L, if we get another impressive convective burst tonight like we have the past couple nights, it may become a little more organized and longer lasting, which would tend to enhance the rainfall threat across the aforementioned areas.



Figure 2. Current wind shear tendency in the path of 92L. Areas of blue lines denote areas of decreasing vertical shear, while areas of white lines denote areas of increasing vertical shear. As you can see from this image, shear ahead of 92L has relaxed substantially compared to just 24 hours ago.

Based on steering data from CIMSS, 92L should continue moving W in the short-term. Also, if you're wondering why I used the low-level steering flow as a basis for the above prediction, it's because presently, 92L isn't a deep enough system to feel the effects of the mid-level steering. Obviously, a weakness in the subtropical ridge is evident at both 700 mb and 500 mb as per the aforementioned steering maps, and 92L will eventually feel this weakness, deep or not. However, based upon steering forecasts from PSU, I do not think that the weakness will begin pulling it more poleward until around around four days, when the system should be exiting the northern coast of Cuba and entering the southeastern Gulf of Mexico.

My forecast track takes 92L across the entire length of Hispaniola beginning in about 18 to 24 hours, briefly emerging back into the Caribbean and making landfall across extreme eastern Cuba by around 42 to 48 hours. By around 80 to 86 hours, whatever is left of the system should begin to emerge off the northern coast of Cuba, and into the southeastern Gulf of Mexico. Thereafter, the models are unanimously indicating a turn to the WNW as 92L begins to feel the effects of the aforementioned weakness in the subtropical ridge. Beyond four days, there are some indications that the ridge could rebuild westward a bit. There is an equally likely possibility, however, of 92L continuing westward, completely missing the Greater Antilles, nearing 85W, and then turning more poleward. Perhaps needless to say, there is a large degree of uncertainty in my current forecast.

Should 92L make it into the Gulf of Mexico, upper-level winds will be favorable for development. However, I give 92L's chances of developing into a tropical cyclone in the Gulf at only about 10%.

Elsewhere

Elsewhere in the tropics, the GFS and NOGAPS are suggesting that a tropical cyclone could develop east of Nicaragua in about three days. This system would quickly run westward into Central America, and does not presently appear to be a threat to the United States. Upper-level winds will be favorable for development here.

The models have been less bullish recently on the prospects of a tropical cyclone developing near and then subsequently passing through the Windward Islands in about a week. However, they still indicate an active ITCZ in the area in about 6 to 7 days, so this will still need to be carefully monitored. Upper-level winds will be extremely favorable for development in this area.

Updated: 12:04 AM GMT on June 19, 2010

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Tropical weather analysis - June 17, 2010

By: KoritheMan, 12:47 AM GMT on June 18, 2010

Began writing at around 7:40 PM eastern

Invest 92L simply refuses to give up. Deep convection has once again reignited, though it is still disorganized due to strong upper-level shear. My best estimate of the center location, based on the last of the visible satellite animations, a recent AMSUB microwave pass, and 850 mb vorticity data, courtesy of University of Wisconsin CIMSS is 17N 58W. Satellite images strongly indicate a struggling, sheared system, with the center displaced well to the west of the large unorganized convective mass. CIMSS diagnoses this westerly shear at 30 kt. A slight weakness is noted in the subtropical ridge to the north of the system around 700 mb. This weakness can also be recognized at 500 mb, as well. This weakness can also clearly be seen on the limited availability of water vapor animation, though this weakness is very slight. Steering current forecasts from PSU are divided. I personally believe the GFS is too far north, and the CMC too far south. Hence, I have opted to split the difference and forecast a gentle WNW movement throughout the forecast period. At the end of the forecast period, after the system enters the Gulf of Mexico, there are indications within the models that the subtropical ridge could strengthen a bit, forcing a more W component of motion thereafter. It is much too early to tell where exactly this system will go when it reaches the Gulf of Mexico, but residents all along the Gulf Coast from Mexico to Florida should carefully monitor the progress of this system.

My current track takes the system across the northern Leeward Islands and Puerto Rico in three days, and then across extreme northeastern Hispaniola after that. Because of the likelihood of land interaction, any development will be highly limited in the short-term. Long-term, it appears that vertical shear will be considerably lessened as the system continues WNW north of the Greater Antilles. Indeed, upper-level winds will be very favorable in the Gulf of Mexico at the end of the forecast period, with the GFS indicating a 200 mb anticyclone over the eastern portion of the region. However, despite this forecast, I am not expecting 92L to rapidly regenerate once it clears the islands and the upper-level flow improves. Why? Because of its structure. Although I must say, a weak tropical storm ultimately impacting a portion of the Gulf Coast is certainly not out of the realm of possibility. However, it is much too early to assert this with any reasonable degree of confidence. Just keep an eye on it for now, and don't panic due to the oil spill.

In the short-term, the central and northern Leeward Islands, Puerto Rico, and Hispaniola, particularly the northern and eastern reaches, will experience heavy rainfall and wind gusts in excess of 30 to 35 kt as 92L passes through.

Elsewhere

The GFS has been hinting, off and on for the last day or so, the possibility of a tropical cyclone developing southeast of the Windward Islands in about a week. From 0z to 12z, it had the system developing (three consecutive runs). However, in the most recent run, the 18z run, it drops it. The ECMWF also no longer shows it as it did around two days ago. However, we can still get an overall idea of what the atmospheric pattern is likely to be during this time, and it is one of an active ITCZ in the area, so this certainly bears monitoring. Upper-level winds will be near zero, with the GFS building a weak anticyclone over the eastern Caribbean by day seven.

Updated: 12:50 AM GMT on June 18, 2010

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Tropical weather analysis - June 15, 2010

By: KoritheMan, 3:26 AM GMT on June 16, 2010

Began writing at around 10:30 PM eastern

Invest 92L did not become a tropical depression today, just as I had expected. However, over the last couple hours, deep convection, the deepest of its life (with cloud tops to -80C in some locations) thus far, has developed and expanded in both intensity and areal coverage. The center is difficult to pinpoint, but I estimate it is near 14N 47W, based on animation of shortwave infrared satellite imagery. This is not certain, however. An earlier ASCAT pass indicated only a sharp wind shift associated with the system, not a closed circulation. Obviously, unless this occurs, this current impressive burst of convection means absolutely nothing. Satellite imagery also confirms the findings of the aforementioned ASCAT pass, with a noticeable lack of westerly winds along the south side of the circulation. Animation of water vapor imagery indicates a large area of dry rapidly advancing toward 92L from the southwest, due to strong southwesterly upper-level shear, diagnosed at 20 to 30 kt as per CIMSS data.



Figure 1. Latest infrared satellite image of Invest 92L.

As this shear continues to gradually push the dry air toward 92L, I expect the current burst of convection to wane overnight and into the morning, as has been the case throughout the system's existence. I honestly don't see a conceivable way for the system to maintain its current deep convection, as southwesterly shear will continue to impinge upon the system, completely preventing the establishment of upper-level outflow along the southwest quadrant of the system, which will in turn allow the dry air to tirelessly ingest into the system. Analysis of vorticity data from CIMSS indicates that the system's cyclonic vorticity has become much better organized over the last 12 hours, but also indicates that the aforementioned southwesterly shear has decoupled the low- and mid-level circulations.

92L is currently moving NW based on my estimations, though this is highly uncertain. I am most in agreement with the NOGAPS' steering forecast, which is for the current NW motion to end shortly, probably within the next 12 hours or so, after which a continued general WNW movement can be expected. On this forecast track, 92L will be passing through the north-central Leeward Islands in about four days, and could bring some locally heavy rainfall and gusty winds to those islands, as well as Puerto Rico and possibly Hispaniola, as well. Thereafter, the system should traverse north of the Greater Antilles, and could eventually find its way to the Bahamas or south Florida. However, this is highly speculative and should be treated as such.

More importantly, the models, the GFS in particular, are hinting at a substantial relaxation of the shear in the Caribbean beginning in about two days and persisting throughout the forecast period. This is because these models lift the TUTT off to the north, out of the Caribbean. The models have been consistent with this, and so this is definitely worth keeping an eye on. So by the time 92L approaches the Leeward Islands and enters the eastern Caribbean Sea, assuming that it retains a decent overall structure, organization into a tropical cyclone is not outside the realm of possibility. Its structure has to survive the upcoming shear first, though. I give this a 20% chance of ultimately becoming a tropical cyclone. Residents across the Leeward Islands, Puerto Rico, and Hispaniola should carefully monitor the progress of this system.

After the system passes the Leewards and Puerto Rico, it will once again encounter unfavorable westerly to southwesterly flow associated with the TUTT, whose axis will be centered north of the Greater Antilles at that time.

Elsewhere

Elsewhere, a tropical wave, as per the 1800 UTC surface analysis from the National Hurricane Center, is located south of 11N along 27-28W, moving W at 5 to 10 kt. Yesterday, I was quite concerned with this wave, but given its currently disorganized state (most of the precipitation is not associated with the wave, but with the ITCZ), along with the forecast of 15 to 20 kt of westerly shear, I am not expecting development of this feature.

More of note, the CMC, GFS, NOGAPS, and ECMWF forecast a tropical wave could pose a threat to develop into a tropical cyclone as it nears or enters the eastern Caribbean by day 6 to 10. The latter is quite a long range forecast. Also, the fact that each model offers a different timing for the system leads me to believe that we do not know the specific date at which this tropical wave will enter the area, if it does at all. However, I do believe that this is worth keeping an eye on, since the ECMWF has been forecasting it since last night. Upper-level winds should be at least marginally conducive for some development of the system.

Updated: 3:55 AM GMT on June 16, 2010

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Tropical weather analysis - June 14, 2010

By: KoritheMan, 11:44 PM GMT on June 14, 2010

Analysis began 5:38 PM EDT

Invest 92L, much to my surprise, did not become a tropical depression this morning. It appears that a burst of southerly shear impinged upon the system this morning, significantly disrupting its previously impressive organization. Estimated center position based on the last of the visible satellite animation loops is 11N 42W. Clearly, this system has gained considerable latitude since this time yesterday, when it was still at 7 to 8N. This gain of latitude is important, because the further away from the equator a storm is, the greater amount of spin is available thanks to the Coriolis Force. This in turn allows a better chance for tropical cyclogenesis, since, obviously, tropical cyclones contain a lot of cyclonic vorticity. The system is currently moving WNW, based on various satellite animations. Also, the southern half of the circulation is slightly exposed south of the deep convection, which is elongated S to N and not well-organized. Analysis of water vapor animations as well as University of Wisconsin CIMSS wind shear data indicates that 92L is experiencing about 20 kt of southwesterly vertical shear on its western side. The catalyst for this shear is a large and persistent TUTT (Tropical Upper Tropospheric Trough) located across the central Caribbean.



Figure 1. Latest infrared satellite image of Invest 92L, at around 7:44 eastern time.

However, this shear has not penetrated the core just yet, as evidenced by the greater convective organization there. Overall, low- to mid-level vorticity has become better organized today, though it is still not perfectly aligned in the vertical. As per CIMSS analysis, upper-level divergence and low-level convergence have remained constant throughout the day, with the latter actually slightly increasing over the last three hours. This will support continued convective development, since dry air not an issue. However, I think the models are grossly overestimating the magnitude of the current shear, and I am not expecting 92L to become a tropical depression, at least in the near-term. At most, it has a 24 hour opportunity with which to intensify before shear gets even stronger. And even that estimate seems a little generous based on what I see.

However, beginning in around 72 hours, models unanimously predict a substantial relaxation of the TUTT. By this time, 92L should be nearing the Leeward Islands. Assuming its structure isn't too disrupted by the current hostile environment, it may have a greater shot (relative to this morning) at becoming a tropical depression during this time, and beyond. I am expecting a continued WNW movement throughout the period, albeit with brief oscillations to the north and south. Smoothing out all of the wobbles leads me to a mean WNW motion toward the central Leeward Islands in about four days. Regardless of development, locally heavy rainfall and strong gusty winds are a strong likelihood across the Leeward Islands and Puerto Rico in about four to five days, and residents in those locations should carefully monitor the progress of this system.

Elsewhere

Elsewhere, as per 1200 UTC analysis from the National Hurricane Center, a tropical wave is noted from 2N to 12N 25W, moving W. This wave has been generating persistent deep convection for nearly 24 hours, and certainly bears watching. Upper-level winds appear rather conducive for development of this system over the next several days. A general W movement should continue with this system over the next several days. This system might be the one to watch, not 92L.

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Tropical weather analysis - June 13, 2010

By: KoritheMan, 10:36 PM GMT on June 13, 2010

Analysis began near 5:30 PM EDT

Invest 92L remains quite vigorous across the eastern tropical Atlantic, having survived the overnight hours. This is a true testament to its persistence, as most waves quickly fizzle out within just a day or so after displaying some vigor, even during the peak of the season. Even more remarkable it is that we are experiencing something like this during only the second week of June!

The last of the visible satellite animation loops, along with shortwave infrared satellite loops suggest that the center is located near 8N 37W. This is a rather low latitude, and few tropical cyclones have developed this far south historically. However, these same loops also indicate that the circulation is still quite broad and elongated. Current 850 mb vorticity data also strongly suggests this, with another cyclonic vorticity maximum depicted very near 40W. This particular gyre appears rather weak and disorganized compared to the stronger one to the east, near 37W, and so I am certainly not expecting this circulation to become the dominant one. Deep convection is also considerably lacking near this circulation, further suggesting that the 37W circulation will remain the dominant gyre.



Figure 1. Latest infrared shortwave IR of Invest 92L. Notice the well-defined spiral banding pattern as well as the large and well-organized upper-level anticyclonic outflow pattern aloft. This indicates that the wave's structure is well-organized, unusually so for June, or even July in this part of the Atlantic.

Though presently, deep convection is rather nil near the estimated center position, the convection within the vicinity of the center appears to be taking on a banded appearance, attempting to gradually band into the center, which indicates increasing organization. In fact, the current structure of well-defined spiral banding and minimal convection near the center is very typical of a tropical cyclone in its formative stages, though it obviously still needs more persistent deep convection, as well as a larger coverage of it, in order to be classified. Dry air is certainly not a problem for 92L, as animation of water vapor imagery indicates a large plume of moisture surrounding the system, as does CIMSS total precipitable water values, with a substantial increase in moisture coverage in just a single day.

Vertical shear is currently light over the system, only 5-10 kt, out of the south. This pattern is especially conducive for continued deepening of 92L. Additionally, a weak anticyclone appears to be centered near the estimated center of 92L, aiding in ventilation of the system. Models suggest that the shear will remain low throughout the next 48 hours, at which point it will increase sharply in association with a persistent TUTT draped across the central Caribbean. This should begin to weaken the system by that point, and it should dissipate well before reaching the central or northern Leeward Islands in the next 5 days or so. However, locally heavy rainfall and strong gusty winds will be a likelihood across those islands as the wave tracks in that general vicinity by that time. All in all, the steering pattern hasn't changed appreciably since this time yesterday, and my current thinking is still that the system eventually moves through the central Leeward Islands.

Current movement is estimated to be slowly WNW, and models suggest this motion should continue throughout the period, albeit with oscillations both north and south. The 12z NOGAPS depicted a track straight WNW, and very close to the central Leeward Islands. I believe that this is the best solution for now, though I am ever so slightly further south in my own forecast.

I do believe this will become a tropical depression in about 12 to 18 hours. However, it is only has a very short window of opportunity with which to intensify. Both the GFDL and HWRF dissipate this system well before reaching the islands. It should be noted that the further south or north the system tracks, the less shear it will encounter, as opposed to what it will if it continues moving straight WNW.

Synopsis in layman's terms

An unseasonably strong tropical wave located in the eastern Atlantic several hundred miles southwest of the Cape Verde Islands continues to display signs of organization. A tropical depression could form from this area over the next day or so before upper-level winds become unfavorable for additional development. I am expecting this system to become a tropical depression sometime tomorrow morning.

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Tropical weather analysis - June 12, 2010

By: KoritheMan, 9:57 PM GMT on June 12, 2010

A vigorous tropical wave, more typical of early August than June, has just been designated "Invest 92L" by the National Hurricane Center.



Figure 1. Current infrared satellite image of Invest 92L, courtesy of the National Hurricane Center.

The last of the visible satellite animations indicate that the axis of this wave is located near 6N 31W. Extrapolation of an earlier ASCAT pass would also yield this estimate. Surface winds are probably around 20-25 mph near the estimated center position. Vertical shear over the system is light, around 10 kt. Vertical shear is forecast to be marginally favorable for slow development of this system for the next 60 hours or so, after which point, the system should encounter strong upper-level westerlies associated with a large and persistent TUTT (Tropical Upper Tropospheric Trough) centered across the central Caribbean Sea. As far as movement is concerned, the system is currently moving slowly WNW, and this should continue throughout the forecast period. This will bring the system near the Leeward Islands and Puerto Rico by around 6 days.

This system only has around 60 hours to coalesce into a tropical cyclone, so we'll see how that goes. Water vapor loops indicate that dry air within the vicinity of the system is fairly minimal at the moment. Obviously, this will tend to favor continued intensification in the short-term, though we'll have to see how moist the environment stays over the next couple of days. As long as the convection continues to be enhanced by the ITCZ, as is currently the case, then the overall environment should remain rather moist, and favor additional development.

All in all, I'd give this system a 20% chance of becoming a tropical cyclone over the next 48 hours. It should be noted that anything higher than a 35 kt tropical storm looks terribly unlikely. However, the significance of this wave lies not in its possible intensity, but rather, it's possible development. If it develops into a tropical cyclone, named or otherwise, then we are very likely in for a very active season ahead, as any time we get tropical cyclones in the deep tropics during June and July, it is almost always a harbinger of an above normal season. This was most recently the case in 2008 with Hurricane Bertha, and before that, in 2000, when Tropical Depression Two formed just offshore western Africa during the final days of June. Both of those seasons were well above average.

None of the computer models are developing this area, but it bears watching. Climatology would certainly argue against it, however.

Updated: 10:05 PM GMT on June 12, 2010

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Tropical weather analysis - June 1, 2010

By: KoritheMan, 7:31 PM GMT on June 01, 2010

The remnants of former Eastern Pacific Tropical Storm Agatha were recently designated an invest (91L), just around 150 miles east of the coast of the Yucatan Peninsula. I must say, this was quite a surprise, as I would not have expected the system to generate this much symmetrical convection, given how disrupted the structure was from passage over Central America.

Invest 91L

The overall organization of the system is quite poor at present, however. Visible satellite imagery depicts a broad circulation without any real surface reflection. I place the poorly-defined surface center near 19N 87W, though this is highly speculative, given the broad nature of the system, as well as the fact that deep convection is covering a portion of the alleged center. Interestingly enough, surface pressures are falling across several reporting stations in the area, including some from Belize, and some from the Yucatan Peninsula of Mexico. Given this, one could safely assume that a low pressure area is attempting to form with this area. CIMSS analysis depicts 20 kt of westerly shear blowing across where I estimate the center to be. Every model, save the NOGAPS, predict that this shear will continue. Obviously, this will make regeneration into a tropical cyclone unlikely (though not impossible). The NOGAPS is a notable exception, however, moving an anticyclone near the region in about 36 hours. I would be concerned about this, but none of the other models foresee this, and CIMSS observations contradict this.

As far as timing goes, I feel the GFS has the best handle on the system, with a very slow, less than 5 mph, motion to the NW or NNW for the next 12 hours. Thereafter, the system should gradually begin turning to the N with some acceleration as a shortwave trough approaches the system from the west. Steering currents will then briefly weaken again for about 12 hours or so, then strengthen significantly thereafter. This should bring the system near the west coast of Florida by around 48 hours. The NOGAPS and CMC keep the trough weaker, and further to the north, which would delay the turn to Florida by about a day or so. I'm inclined to agree with the GFS with regards to speed, due to the fast southwesterly flow currently present across the Gulf of Mexico. The system should be very near the western Florida peninsula by this time on June 3.

As far as intensity is concerned, as I mentioned earlier, models maintain the currently westerly shear. Additionally, shear becomes destructively unfavorable across the entire Gulf of Mexico, owing to the typical and persistent subtropical jet. Models do not foresee any real relaxation of this shear in the foreseeable future. Hence, I feel the chances of this system regenerating are rather low. I agree with the NHC, giving the remnants of Agatha a 10% chance of becoming a tropical cyclone in the next 48 hours. It could produce locally heavy rainfall across portions of central and southern Florida, however.



Figure 1. Visible satellite imagery of the Caribbean as of 2:30 PM CDT. 91L is on the far left, near the coast of the Yucatan Peninsula.

Elsewhere

The only other area of note in the basin today is a westward-moving tropical wave, currently evident from Panama northward into the southwest Caribbean. While this area is not currently displaying any significant organization, the NOGAPS has been persistent in developing this area into a tropical cyclone for the last several days. The GFS hints at development, but in the East Pacific. It is uncertain which model will win out, if any, but I prefer the GFS. Upper-level winds are quite favorable in this area, with an anticyclone evident at 250 mb upward, its axis centered just south of eastern Cuba. I will continue to monitor this area carefully over the coming days. This system should move W in the short-term.

Updated: 7:34 PM GMT on June 01, 2010

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About KoritheMan

I'm just a 23 year old with an ardent passion for weather. I first became aware of this interest after Tropical Storm Isidore struck my area in 2002.

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