Good evening everyone!
The remnant of Dorian was designated INVEST 91L earlier today. I will be using these terms interchangeably in the synopsis.
The current STWO (Special Tropical Weather Outlook) from the NHC indicates the remnant is a sharp surface trof as found by reconnaissance aircraft.
ZCZC MIATWOAT ALL TTAA00 KNHC DDHHMM SPECIAL TROPICAL WEATHER OUTLOOK NWS NATIONAL HURRICANE CENTER MIAMI FL 350 PM EDT SUN JUL 28 2013 FOR THE NORTH ATLANTIC...CARIBBEAN SEA AND THE GULF OF MEXICO... 1. DATA FROM AN AIR FORCE RECONNAISSANCE MISSION IN THE REMNANTS OF DORIAN...LOCATED A COUPLE HUNDRED MILES NORTH OF THE LEEWARD ISLANDS...INDICATE THAT THE DISTURBANCE DOES NOT HAVE A WELL- DEFINED CENTER OF CIRCULATION AND CONSISTS OF A SHARP SURFACE TROUGH. THE SYSTEM IS PRODUCING WINDS TO GALE FORCE WELL NORTH OF THE LEEWARD ISLANDS...HOWEVER THE ASSOCIATED SHOWER AND THUNDERSTORM ACTIVITY HAS WEAKENED DURING THE PAST FEW HOURS. ENVIRONMENTAL WINDS ARE EXPECTED TO BE ONLY MARGINALLY CONDUCIVE FOR REGENERATION DURING THE NEXT COUPLE OF DAYS. THIS SYSTEM HAS A MEDIUM CHANCE...30 PERCENT...OF BECOMING A TROPICAL CYCLONE DURING THE NEXT 48 HOURS AS IT MOVES WESTWARD TO WEST-NORTHWESTWARD AT AROUND 20 MPH...PASSING NORTH OF THE LEEWARD ISLANDS AND PUERTO RICO THROUGH MONDAY...AND MOVING OVER THE TURKS AND CAICOS ISLANDS AND SOUTHERN BAHAMAS ON TUESDAY. ADDITIONAL INFORMATION ON THIS SYSTEM CAN BE FOUND IN HIGH SEAS FORECASTS ISSUED BY THE NATIONAL WEATHER SERVICE...UNDER AWIPS HEADER NFDHSFAT1 AND WMO HEADER FZNT01 KWBC. ELSEWHERE...TROPICAL CYCLONE FORMATION IS NOT EXPECTED DURING THE NEXT 48 HOURS. FORECASTER BERG
Upon my previous forecast, based on the last time I analyzed model data, data at the time did not support any regeneration of Dorian. Upon researching back, I did notice, the steering layers forecast maps had in fact moved the remnants a little too quickly than what they have actually been moving…in fact, the current run of the steering layers forecast maps has 91L further west than what it actually is at this time.
The current wind shear product from CIMSS, does show a developing upper level anticyclone over the disturbance at the moment. Another positive factor is, the TUTT to it’s west continues to move W-WNW in tandem with the system, thereby instead of having a negative effect, is just far enough from the disturbance to allow for ventilation over the ex-Dorian.
The upper level wind diagram does show a fairly robust upper level northern outflow channel, or jet if you will, with modest outflow around the southern periphery of the system.
INVEST 91L seems to have mixed out quite a bit of drier air, and may be able to continue this, as the further west it moves, it will be crossing over some moderate TCHP values, which can help add moisture to the system.
The latest run (12Z) of the GFS Zonal Shear forecast tends to indicate upper level conditions may not remain as hostile as first thought a couple of days ago. The scenario calls for a waxing and waning of the upper level anticyclone over the next 48 hours, however the average indicates the upper level feature to remain over 91L during the next 48 hours. Based on latest model guidance track, INVEST 91L should be withing little, to zero zonal shear thereafter.
Based on this, I believe ex-Dorian, may have a better than average chance at regeneration over the next 48-72 hours.
Analysis of various satellite loop imagery channels, current and forecast steering layers maps, I tend to concur with the 18Z Dynamic Model Guidance, and prefer the TVCC/TVCN guidance track. However, based on the forecast steering layers maps, I believe the model guidance may shift right, as the trof that will create the weakness will be slower to lift out than previously forecast.
As a precaution…not saying that regeneration is definite…residents of the Florida Peninsula should monitor the progress of this system over the next 72 hours.
I should have another update tomorrow afternoon after my meeting with USCG Air Station Clearwater.
Have a blessed evening!
T. F. “STORM” WALSH III
GMCS, USCG (ret)
METEOROLOGIST / HURRICANE SPECIALIST
MEMBER WEST CENTRAL FL AMS
CERTIFIED SKYWARN OFFICIAL STORM SPOTTER (advanced)