ZCZC MIATCDAT3 ALL TTAA00 KNHC DDHHMM TROPICAL STORM GABRIELLE DISCUSSION NUMBER 10 NATIONAL WEATHER SERVICE MIAMI FL 11 PM EDT THU SEP 13 2001 FIXES FROM THE AIR FORCE RESERVE HURRICANE HUNTER MONITORING GABRIELLE EARLIER THIS EVENING INDICATED AN ERRATIC MOTION... FIRST JUMPING ABOUT 20 NM TO THE WEST AND THEN ABOUT 30 NM TO THE EAST. THE CENTRAL PRESSURE DROPPED TO 996 MB...WITH A SECOND LATER FIX OF 997 MB AND 52 KT FLIGHT LEVEL WINDS. SATELLITE IMAGERY INDICATES THAT THE STORM IS AT LEAST SOMEWHAT SHEARED...WITH BURSTS OF CONVECTION DEVELOPING TO THE EAST OF THE CENTER. THE INITIAL INTENSITY IS 45 KT IN AGREEMENT WITH ALL SATELLITE INTENSITY ESTIMATES AND THE AIRCRAFT WINDS. THE INITIAL MOTION IS VERY UNCERTAIN BUT IS ESTIMATED TO BE 055/4. WATER VAPOR IMAGERY AND DATA FROM THE NOAA G-4 JET SHOW A SHARP MID/UPPER LEVEL TROUGH JUST WEST OF THE CYCLONE...WHILE LOW LEVEL RIDGING SURROUNDS THE SYSTEM. THE RIDGING SUGGESTS THE MOTION SHOULD REMAIN SLOW...AT LEAST INITIALLY. NHC HURRICANE GUIDANCE AGREES ON A SLOW NORTHEASTWARD MOTION FOR THE FIRST 36-48 HR WITH SOME ACCELERATION THEREAFTER. THE TRACK FORECAST FOLLOWS THE GUIDANCE AND IS BASICALLY AN UPDATE OF THE PREVIOUS PACKAGE. SOME ERRATIC MOTION IS LIKELY AS THE CENTER RE-FORMS DUE TO THE CONVECTIVE BURSTS. THE G-4 DATA INDICATES CONSIDERABLE UPPER LEVEL DIFLUENCE OVER GABRIELLE FROM THE UPPER LEVEL TROUGH AND AN UPPER LEVEL RIDGE TO THE SOUTHEAST. WHILE LARGE-SCALE MODELS INDICATE THAT SOME WESTERLY SHEAR SHOULD CONTINUE OVER THE STORM...DIVERGENCE FROM THE TROUGH AND ASSOCIATED UPPER LEVEL WIND MAXIMA WILL LIKELY MAINTAIN STRONG CONVECTION WITH THE SYSTEM AND ALLOW FOR SOME STRENGTHENING. THE INTENSITY FORECAST BRINGS GABRIELLE TO 60 KT AT LANDFALL...AND THERE IS A CHANCE IT COULD BE A HURRICANE AT THAT TIME. AT THIS TIME...IT APPEARS THAT THE MAIN THREAT FROM GABRIELLE IS VERY HEAVY RAINFALL AND POTENTIAL FLOODING. HEAVY RAINBANDS ARE ALREADY SPREADING ONSHORE OVER THE SOUTHERN FLORIDA PENINSULA AND KEYS. FORECASTER BEVEN FORECAST POSITIONS AND MAX WINDS INITIAL 14/0300Z 25.5N 84.0W 45 KTS 12HR VT 14/1200Z 26.0N 83.4W 50 KTS 24HR VT 15/0000Z 27.0N 82.4W 60 KTS 36HR VT 15/1200Z 28.1N 81.4W 50 KTS 48HR VT 16/0000Z 29.0N 80.5W 45 KTS 72HR VT 17/0000Z 31.0N 77.0W 50 KTS NNNN