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(T. F. “Storm” Walsh III)
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Good evening everyone!
The NHC has designated the tropical wave in the Atlantic INVEST 92L, and the area of low pressure which has developed over the Gulf of Honduras, INVEST 93L. NHC has designated a HIGH (80%) probability of cyclone formation IRT INVEST 93L, and a MEDIUM (60%) probability of cyclone formation IRT INVEST 92L, during the next 5 days.
We’ll begin closer to home first.
INVEST 93L is an area of low pressure located or centered over the extreme Western portion of the Gulf of Honduras. This is the area where models have been showing, and I’ve been speaking, of lowering pressure heights for over a week now.
As of the 18Z ATCF BTK report, the following was available on INVEST 93L:
MAX SUSTAINED WIND: 30 mph
PRESSURE: 1007 mb / 29.74″
MOVEMENT: NW 6 mph
Analysis of satellite loop imagery indicates convection has increased over the past few hours, mainly east of the center.
Analysis of the current wind shear map indicates 93L is still under approximately 20 kts of wind shear at the moment. However, you’ll notice the upper level anticyclone (clockwise turning of the streamlines) to the south of the center, and an outflow jet becoming established north and NE of the system as seen in the upper level winds map. Based on the recent wind shear forecast from the GFS, 12Z run, upper level wind shear forecast to improve over the next 24 hours, and this upper level anticyclone should become positioned over the center, or very close to the center. This feature is forecast to move in tandem with 93L over the next 72 hours. Based on this analysis, and analysis of the current TPW map, indicating a high TPW content, INVEST 93L should begin to become better organized, especially once it enters into the GOMEX, however there could be a chance of some drier air influencing the system later on, as noted in analysis of water vapor loop imagery. Further organization should be slow to occur. Based on the same wind shear forecast, provide no major changes occur, I don’t anticipate 93L becoming very strong, based on the fact the upper level anticyclone may not be optimal, but more of an elliptical feature. There would be some outflow aloft, however it could not be sufficient enough to allow for any appreciable strengthening. Based on the initial intensity model guidance, models at the moment, only bring 93L to minimal T.S. at best, while the majority show only a T.D. Of course, this will change, as the initialization has just taken place and modeling should come more into consensus once we have an organized low.
WIND SHEAR AND UPPER LEVEL WINDS FROM CIMSS
GFS WIND SHEAR FORECAST
93L ATCF 18Z INTENSITY FORECAST (INITIAL)
Based on analysis of statistical and dynamic model guidance, which are sparse at this time (18Z), modeling is pretty much in different directions as far as future motion of this system. The GFS and what statistical models were available at the time, indicate this system coming due north, and affecting anywhere from LA to the FL. Panhandle, while the only 2 dynamic models indicate this heads toward TX. The ECMWF suggests more of a west motion inline with the dynamic guidance TVCX, coming into Mexico, then affecting extreme southern TX. Now, I know everyone is anxious to know where this may be heading, however, everything I just pointed out is INITIAL…In other words, ACCURACY is VERY LOW at the moment. In order to achieve good track guidance, and you’ve heard me repeat this millions of times, WE HAVE TO HAVE A WELL ORGANIZED, CLOSED, LLC (Low Level Circulation). From experience, it will probably take another 3-4 runs of the models, until we even see a half good consensus. I wouldn’t look for really accurate track guidance, until this clears away from the Yucatan, and enters the GOMEX. I know you’d like more, but professionally, that’s all I can give you right now. Analysis of MSLP anomaly maps turned out to be fairly inconclusive upon tonight’s analysis. However, we still have time with this.
93L 18Z INITIAL TRACK GUIDANCE
Elsewhere, the tropical wave in the CATL had been designated as INVEST 92L earlier, by the NHC. As of the 18Z ATCF BTK report, the following was available on INVEST 92L:
MAX SUSTAINED WIND: 30 mph
PRESSURE: 1009 mb / 29.80″
MOVEMENT: W 18 mph
Analysis of satellite loop imagery this evening indicates INVEST 92L appears a little less organized than it did yesterday. It still displays notable circulation, however the structure is not as “tight” as it was yesterday, and convection is more limited this evening.
Based on analysis of the current shear map, wind shear levels are only around 5-10 kts. However, the upper level anticyclone that was providing outflow aloft, has collapsed, and there doesn’t appear to be any outflow channel noted in the upper level winds map.
WIND SHEAR MAP FROM CIMSS
UPPER LEVEL WINDS
In addition to this, 92L is encountering some other negative factors at the moment. The area of TPW is not as extensive, and TPW values are not as high as they were earlier. TPW is still sufficient, however limited to a very small area. There are two other tropical waves behind 92L. These waves are a little stronger than 92L appears at this time, and these may be taking energy away from 92L at the moment. This is why I always mention, that for a wave, or depression to really get going, it needs to cross out of the ITCZ. And last, the forward speed of this wave s not allowing for good surface convergence to occur.
However, upper level winds are forecast to improve over the next 24 hours, and a small upper level anticyclone could become established. Once 92L enters into the Caribbean though, upper level winds collapse once more, and then wind shear is forecast to increase.
GFS WIND SHEAR FORECAST 72 HOURS
Current intensity models indicate 92L to become a minimal T.S. in about 36-48 hours, and I cannot rule this out, if conditions improve.
INVEST 92L 18Z INTENSITY FORECAST
Based on analysis of dynamic model guidance, 92L should continue toward a W to WNW motion, and should enter the extreme southern Caribbean Sea after crossing the Windward Islands in about 4 – 5 days. Based on the uncertainty at this time regarding strength, I prefer the TVCA / TVCX consensus guidance, which is close to the ECMWF EPS track
INVEST 92L TRACK GUIDANCE
I will be monitoring both areas closely, and should have another update late Sunday afternoon. I only have 3 forecast days this week…Sunday included, as I work WED – SAT. However, IF any significant changes occur, I will be working late to provide an update.
Elsewhere, I am monitoring 2 tropical waves in the far eastern Atlantic, which are behind INVEST 92L. Based on the current wind shear forecast, upper level winds could remain marginally to slightly conducive over the next 72-96 hours for some further, slow organization.
Elsewhere, Tropical Storm formation is not expected during the next 7-10 days.
Have a blessed day!
T. F. “STORM” WALSH III
GMCS, USCG (ret)
METEOROLOGIST / HURRICANE SPECIALIST /SEVERE WEATHER SPECIALIST
MEMBER WEST CENTRAL FLORIDA AMS