ZCZC MIATCDAT1 ALL TTAA00 KNHC DDHHMM TROPICAL STORM FAY DISCUSSION NUMBER 13 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL062008 500 PM EDT MON AUG 18 2008 SATELLITE...RADAR...AND AIRCRAFT DATA INDICATE THAT FAY HAS BECOME BETTER ORGANIZED THIS AFTERNOON. THE CONVECTIVE BANDING HAS INCREASED AROUND THE CENTER...AND THE RADIUS OF MAXIMUM WINDS HAS CONTRACTED TO ABOUT 30 N MI. ADDITIONALLY...THE CENTRAL PRESSURE HAS FALLEN TO 998 MB. HOWEVER...THIS HAS NOT YET CAUSED THE WINDS TO INCREASE...AS AIRCRAFT...RADAR...AND SURFACE DATA SUGGEST THE MAXIMUM WINDS REMAIN ABOUT 50 KT. IT SHOULD BE NOTED THAT A TCU WAS ISSUED NOTING LANDFALL WHEN THE WINDS AT KEY WEST WENT CALM AT 3 PM. LATER DATA SUGGESTS THIS WAS DUE TO A MESOSCALE FEATURE ROTATING AROUND THE LARGER CENTER OF THE STORM...AND THE TRUE CENTER OF FAY IS OVER KEY WEST NOW. THE INITIAL MOTION IS 340/10. FAY IS ENTERING A BREAK IN THE SUBTROPICAL RIDGE OVER THE EASTERN GULF OF MEXICO AND FLORIDA CAUSED BY A MID/UPPER-LEVEL TROUGH MOVING THROUGH THE SOUTHEASTERN UNITED STATES. BEYOND 36-48 HR...THE TROUGH IS FORECAST TO LIFT OUT...WITH A MID/UPPER-LEVEL RIDGE BUILDING OVER THE EASTERN UNITED STATES AHEAD OF A SECOND TROUGH OVER THE WESTERN GULF COAST STATES. THE MODEL GUIDANCE STILL SHOWS CONSIDERABLE SPREAD IN RESPONDING TO THIS PATTERN. THE NOGAPS CONTINUES TO CALL FOR A NORTH- NORTHWESTWARD MOTION TOWARD THE FLORIDA PANHANDLE AND INLAND THEREAFTER. THE UKMET HAS SHIFTED A LITTLE TO THE EAST AND FORECASTS A NORTHWARD MOTION THROUGH THE FLORIDA PENINSULA...WITH A SHARP TURN TO THE WEST AFTER 72 HR. THE CANADIAN MODEL HAS A SIMILAR FORECAST. THE GFS AND ECMWF CALL FOR FAY TO TURN NORTHEASTWARD INTO THE ATLANTIC...FOLLOWED BY A WESTWARD TURN AND MOTION BACK INTO NORTHERN FLORIDA AFTER 72 HR. FINALLY...THE GFDL AND THE HWRF CONTINUE FOR A GENERALLY NORTHWARD MOTION WELL INLAND OVER THE EASTERN UNITED STATES. GIVEN THE INCREASING SIGNAL FROM THE GLOBAL MODELS THAT NEW RIDGE TO THE NORTH WILL BLOCK FAY'S PROGRESS...THE NEW FORECAST TRACK CALLS FOR A SLOWER AND MORE WESTWARD MOTION AFTER 72 HR. THE EARLIER PART OF THE TRACK...WHICH CALLS FOR LANDFALL IN SOUTHWESTERN FLORIDA IN ABOUT 18 HR FOLLOWED BY A TRACK OVER THE FLORIDA PENINSULA...IS SHIFTED A LITTLE TO THE EAST AND LIES NEAR THE MODEL CONSENSUS. WHILE FAY REMAINS IN A MODERATE SOUTHWESTERLY VERTICAL SHEAR ENVIRONMENT AND IS BATTLING DRY AIR ENTRAINMENT...THESE CONDITIONS ARE NOT SEVERE ENOUGH TO PREVENT STRENGTHENING. THUS...THE INTENSITY FORECAST CALLS FOR STRENGTHENING UNTIL LANDFALL. WHILE NOT EXPLICITLY A FORECAST POINT...IT IS LIKELY THAT FAY WILL MAKE LANDFALL AT OR NEAR HURRICANE STRENGTH. AFTER 24 HR...THE INTENSITY WILL DEPEND MAINLY ON WHETHER FAY IS OVER LAND...AS THE UPPER-LEVEL WINDS ARE LIKELY TO BECOME MORE FAVORABLE. THE CURRENT INTENSITY FORECAST IS BASED ON FAY REMAINING OVER LAND AND THUS DISSIPATING. IF FAY REGAINS THE ATLANTIC OR THE GULF OF MEXICO DURING THE FORECAST PERIOD...IT WILL LIKELY REMAIN STRONGER THAN FORECAST. IT SHOULD BE NOTED THAT...SIMILAR TO CHARLEY IN 2004...SMALL DEVIATIONS FROM THE FORECAST TRACK COULD MAKE LARGE DIFFERENCES IN WHEN AND WHERE THE CENTER OF FAY MAKES LANDFALL ON THE FLORIDA COAST. FORECAST POSITIONS AND MAX WINDS INITIAL 18/2100Z 24.6N 81.9W 50 KT 12HR VT 19/0600Z 25.8N 82.0W 60 KT 24HR VT 19/1800Z 27.4N 81.9W 55 KT...INLAND 36HR VT 20/0600Z 28.8N 81.7W 40 KT...INLAND 48HR VT 20/1800Z 30.0N 81.5W 35 KT...INLAND 72HR VT 21/1800Z 31.0N 81.5W 30 KT...INLAND 96HR VT 22/1800Z 32.0N 82.5W 25 KT...INLAND 120HR VT 23/1800Z 33.0N 84.0W 20 KT...INLAND REMNANT LOW $$ FORECASTER BEVEN NNNN
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