971
WTNT45 KNHC 260843
TCDAT5
POST-TROPICAL CYCLONE TAMMY DISCUSSION NUMBER 32
NWS NATIONAL HURRICANE CENTER MIAMI FL AL202023
500 AM AST THU OCT 26 2023
TAMMY APPEARS TO HAVE COMPLETED ITS TRANSITION TO A POST-TROPICAL
CYCLONE, MERGING WITH THE NEARBY FRONT. THE CLOUD PATTERN HAS BECOME
MORE COMMA SHAPED, WITH A LONG LINEAR CONVECTIVE BAND, AND IS NO
LONGER PRODUCING DEEP CONVECTION NEAR THE CENTER. THE CYCLONE IS
NOW FRONTAL BUT LIKELY STILL HAS A WARM CORE, INDICATING THAT IT IS
A WARM SECLUSION-TYPE OF EXTRATROPICAL CYCLONE. DESPITE THE
TRANSITION, IT REMAINS A STRONG CYCLONE, AND THE INITIAL INTENSITY
IS 75 KT, BASED ON CURRENT INTENSITY SATELLITE ESTIMATES.
THE CYCLONE HAS SLOWED DOWN AND MADE A NORTHWARD TURN OVERNIGHT, AND
RECENTLY THE SYSTEM IS TURNING MORE NORTH-NORTHWESTWARD. THE
ESTIMATED LONG-TERM MOTION IS 355/10 KT. OVER THE NEXT DAY OR SO,
TAMMY IS FORECAST TO SLOW DOWN AND MOVE GENERALLY NORTHWESTWARD TO
WEST-NORTHWESTWARD. BEYOND 36 H THERE CONTINUES TO BE HIGH
UNCERTAINTY IN THE TRACK FORECAST, WITH NO MORE CLARITY FROM THE
LATEST GLOBAL MODEL RUNS. THE GLOBAL MODELS CONTINUE TO HAVE
ENORMOUS SPREAD, AND ENSEMBLE SOLUTIONS THAT DIVERGE IN OPPOSITE
DIRECTIONS. GIVEN THE UNCERTAINTY, THERE IS LITTLE CHANGE FROM THE
PREVIOUS FORECAST AT THIS TIME RANGE.
ALTHOUGH POST-TROPICAL, TAMMY REMAINS A POWERFUL CYCLONE. IN THE
NEAR TERM, THE INCREASING SHEAR AND DRIER AIR ASSOCIATED WITH A
DEEP-LAYER TROUGH TO THE WEST SHOULD CONTINUE TO CAUSE CONVECTION TO
DISSIPATE, AND THE SYSTEM TO WEAKEN OVER THE NEXT FEW DAYS. GLOBAL
MODEL FIELDS INDICATE TAMMY COULD SHED ITS FRONTAL STRUCTURE BY 36
H. A REDUCTION IN WIND SHEAR IS FORECAST SOON THEREAFTER, AND
CONVECTION COULD REDEVELOP NEAR TAMMY'S CENTER IN ABOUT 2-3 DAYS
WHILE IT MOVES OVER 25-26C SEA SURFACE TEMPERATURES. THOUGH IT IS
NOT EXPLICITLY FORECAST, THERE IS SOME POTENTIAL BASED ON THE GFS
AND ECMWF SIMULATED SATELLITE IMAGERY THAT TAMMY COULD REACQUIRE
TROPICAL CHARACTERISTICS THIS WEEKEND OR EARLY NEXT WEEK. THE
CHANCES OF THE SYSTEM TRANSITIONING BACK TO A TROPICAL CYCLONE WILL
BE EVALUATED IN ROUTINE TROPICAL WEATHER OUTLOOKS.
THIS IS THE LAST NHC ADVISORY. ADDITIONAL INFORMATION ON THIS SYSTEM
CAN BE FOUND IN HIGH SEAS FORECASTS ISSUED BY THE NATIONAL WEATHER
SERVICE, UNDER AWIPS HEADER NFDHSFAT1, WMO HEADER FZNT01 KWBC, AND
ONLINE AT OCEAN.WEATHER.GOV/SHTML/NFDHSFAT1.PHP
FORECAST POSITIONS AND MAX WINDS
INIT 26/0900Z 30.5N 58.4W 75 KT 85 MPH...POST-TROP/EXTRATROP
12H 26/1800Z 31.2N 59.6W 65 KT 75 MPH...POST-TROP/EXTRATROP
24H 27/0600Z 31.5N 61.0W 55 KT 65 MPH...POST-TROP/EXTRATROP
36H 27/1800Z 31.9N 62.2W 55 KT 65 MPH...POST-TROPICAL
48H 28/0600Z 32.3N 62.1W 50 KT 60 MPH...POST-TROPICAL
60H 28/1800Z 32.4N 61.2W 50 KT 60 MPH...POST-TROPICAL
72H 29/0600Z 32.4N 60.4W 45 KT 50 MPH...POST-TROPICAL
96H 30/0600Z 32.3N 59.6W 40 KT 45 MPH...POST-TROPICAL
120H 31/0600Z 32.2N 58.4W 35 KT 40 MPH...POST-TROPICAL
FORECASTER KELLY
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