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TROPICAL STORM GABRIELLE DISCUSSION NUMBER 8
NATIONAL WEATHER SERVICE MIAMI FL
11 AM EDT THU SEP 13 2001
TWO SURFACE OBSERVATIONS...FROM SHIPS WITH CALL SIGNS DCUW AND
WCZ5238...OF 35 AND 40-KNOT WINDS RESPECTIVELY...AS WELL AS DVORAK
CLASSIFICATIONS OF T2.5 FROM TAFB AND SAB...SUPPORT UPGRADING THE
CYCLONE TO TROPICAL STORM GABRIELLE. THERE IS SOME SOUTHWESTERLY
SHEAR OVER THE SYSTEM BEING CAUSED BY AN UPPER-LEVEL TROUGH TO THE
NORTHWEST. IN FACT...RECENT VISIBLE IMAGES SUGGEST THAT THE CENTER
IS PARTIALLY EXPOSED ON THE WESTERN EDGE OF THE MAIN AREA OF
CONVECTION. THE U.K MET AND AVN MODELS SUGGEST THAT THE UPPER LEVEL
WINDS WILL BECOME MORE FAVORABLE OVER THE NEXT COUPLE OF DAYS...AND
THE SHIPS GUIDANCE SHOWS STRENGTHENING TO A HURRICANE. THE OFFICIAL
FORECAST IS SIMILAR.
THE CENTER CONTINUES TO MEANDER AND THE INITIAL MOTION ESTIMATE IS
QUASI-STATIONARY. THE TRACK FORECAST CONTINUES TO BE PROBLEMATIC.
THE MID-TROPOSPHERIC TROUGH CURRENTLY MOVING INTO THE EASTERN U.S.
DOES NOT APPEAR TO BE INFLUENTIAL ENOUGH TO PICK UP GABRIELLE. THE
NCEP GLOBAL...AVN...MODEL SHOWS A RIDGE BUILDING WESTWARD ACROSS THE
GREATER ANTILLES OVER THE FORECAST PERIOD...AND THAT MODEL PUSHES
THE STORM NORTHWARD AS A RESULT OF SOUTHERLY STEERING ON THE WESTERN
SIDE OF THE RIDGE. THE NOGAPS MODEL CONTINUES TO TAKE THE SYSTEM
GENERALLY WESTWARD...AND THE U.K. MET OFFICE MODEL CONTINUES TO SHOW
LITTLE MOVEMENT. THE CURRENT NHC TRACK FORECAST IS A LITTLE TO THE
LEFT OF THE PREVIOUS ONE AND FAIRLY CLOSE TO THE AVN. THE 06Z GFDL
RUN IS FARTHER WEST AND SOUTH OF MY TRACK. OBVIOUSLY...THERE IS A
GREAT DEAL OF UNCERTAINTY IN THE 48- AND 72-HOUR FORECAST POINTS.
FORECASTER PASCH
FORECAST POSITIONS AND MAX WINDS
INITIAL 13/1500Z 25.2N 85.2W 40 KTS
12HR VT 14/0000Z 25.5N 85.5W 45 KTS
24HR VT 14/1200Z 26.0N 85.5W 50 KTS
36HR VT 15/0000Z 27.0N 85.5W 50 KTS
48HR VT 15/1200Z 28.0N 85.0W 65 KTS
72HR VT 16/1200Z 29.5N 83.5W 75 KTS
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