TROPICAL CYCLONE FORMATION: INVEST 99L (40%) / T.S. GASTON / 91L (30%)
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(T. F. “Storm” Walsh III)
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CURRENT 2016 ATLANTIC TROPICAL CYCLONE TOTALS:
TOTAL STORMS: 7
INTENSE HURRICANES: 0
StormW’s Seasonal Hurricane Forecast:
TOTAL STORMS: 13-15
INTENSE HURRICANES: 3-4
Good evening everyone!
Tropical disturbance INVEST 99L continues to move slowly through the southern Bahamas..Based on the ATCF BTK information, the disturbance may be moving slightly north of due west. However the bulk of the system may be moving to the WNW. As of the 18Z ATCF BTK update, the following was available on INVEST 99L:
2:00 PM AST Sat Aug 27
Location: 23.4°N 78.7°W
Moving: WNW 10mph
Min pressure: 1009 mb / 29.80 in
Max sustained: 30 mph
Recent satellite loop imagery indicates a still disorganized system. Although the last few frames indicated the mid level circulation may be consolidating. I have spent a good amount of time following the IR2 floater channel, which acts as night time visible. I did notice the surface center earlier at around 1400Z in the loop imagery, however it has since become discernible. It is unknown whether it is now obscured by cloud cover, or if the mid level rotation may be becoming the more dominant center, which may be almost caught up to the lower level circulation. In any case, there appears to be some slight fanning out of the cloud cover, and the upper level wind pattern has improved slightly over the past 6 hours.
Wind shear has fluctuated today, and is currently stronger than earlier today. This is due to an upper level low to the north of the INVEST, which was fairly strong earlier. The combination of the flow around this upper low, and the ridge over the Yucatan peninsula tip, is providing 20-25 knots of NW shear over a small portion of INVEST 99L. However, going back in time in the images, the upper low has weakened substantially. This could lead to wind shear relaxing once again.
In fact, this is what the most recent wind shear forecast indicates. IF the shear forecast is correct, 6 global models from the NOAA RUC HFIP diagnostic site, ALL relax shear to favorable levels within the next 24- hours. Analysis of the GFS and ECMWF deep layer shear forecast indicates this as well, with both the GFS and ECMWF in almost remarkable agreement of re-establishing an upper level anticyclone over 99L, after it passes through the FL. Straits. Both models are in agreement of the upper level anticyclone developing just south of the FL. keys, to just WSW of the Keys, in approximately 24-36 hours, and pretty much maintaining this feature in the path projected, whether you’re looking at the GFS track, or ECMWF track.
Based on this, I do believe we should still begin to see better development of this system, once it enters the GOMEX south or WSW of the Florida Keys. Depending exactly on upper level conditions, and exact track, 99L may have the potential to attain hurricane strength in approximately 4 – 5 days. IF the favorable conditions do pan out…I cannot rule this out at the moment.
INVEST 99L continues W to WNW, and I expect this motion to continue during the next 48 hours, with a possible northward turn shortly thereafter. Based on the updated forecast steering layers maps, this seems plausible, and may be inline with the 18Z Dynamic model guidance. However, I must reiterate, track guidance is still not to be considered to reliable at the moment, until IF and WHEN 99L becomes better organized with a solid closed low level circulation to track. I believe the guidance at the moment may be working off the overall system. Forecast steering indicates that a portion of the ridge over the NE United States may begin to weaken, and retrograde toward the west closer to the central portion of the U.S. In addition, it appears as if INVEST 91L currently near Bermuda, may impart a weakness just to the NE of the Florida peninsula by 48-72 hours. Models vary on strength and track with this, with the ECMWF being a little more centered in the GOMEX, then curving it toward the FL. Panhandle as a 90-95 kt hurricane, with other models remaining closer to FL with a weaker system. The CMC GGEM indicates a CAT 1 in the eastern FL. panhandle near 82-83W, and GFS further east toward the Big Bend area with a Tropical Depression. Latest ECMWF EPS members are in between these scenarios, from the extreme western tip of the FL. Panhandle, to the Big Bend area.
At the moment, I know EVERYONE will want to ask where is it going to go, and should I prepare. I am not going to lie or hype this, and the BEST thing I can tell you right now is, I CANNOT tell you for sure, exactly where this is going over the next 24-48 hours. Again, steering on this should be considered preliminary until IF and WHEN it becomes developed. As we have seen in the past 3-4 days, the modeling has shifted pretty much from TX, to FL, to LA, to FL., to MS, to FL. (get my drift). So, I caution you, everybody and their brother is going to try their hand at telling you they know where it will go and it’s going to be speculation at best. It is recommended that residents from AL. to the Tampa Bay area closely monitor this system, until I can get a better handle on it if and when development takes place. For right now, I have to side with the 18Z Dynamic guidance consensus models TVCC / TVCN, however a blend of these and the ECMWF solution may be in order.
Regardless, residents of the Bahamas and the Florida Peninsula, especially areas of S. Florida and central Florida should be prepared for some heavy rainfall over the next few days, which could cause flooding on lower areas, and some Urban flooding. From the NHC in Miami:
Gusty winds and locally heavy rainfall are likely over portions of the Bahamas, and will spread into parts of southern Florida and the Florida Keys by Sunday. Interests elsewhere in Florida and the eastern Gulf of Mexico should continue to monitor the progress of this disturbance.
I don’t have time this evening to spend on 91L, but will try and touch on it tomorrow. Another wave is expected to exit Africa around Tues, and definitely may bear watching.
I do intend on having an update probably closer to early evening tomorrow.
Have a blessed evening!
T. F. “STORM” WALSH III
GMCS, USCG (ret)
METEOROLOGIST / HURRICANE SPECIALIST /SEVERE WEATHER SPECIALIST
MEMBER WEST CENTRAL FLORIDA AMS