[Tropical] Tropical Cyclone Discussion

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WTNT41 KNHC 181504
TCDAT1
TROPICAL STORM FAY DISCUSSION NUMBER  12
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL062008
1100 AM EDT MON AUG 18 2008

THE CENTER OF FAY HAS MOVED INTO THE FLORIDA STRAITS.  SATELLITE
IMAGERY AND RADAR DATA SHOW STRONG CONVECTIVE BANDING OVER THE
EASTERN SIDE OF THE STORM...BUT LITTLE ACTIVITY IN THE WESTERN
SEMICIRCLE.  THIS ASYMMETRY IS LIKELY DUE TO WESTERLY VERTICAL
SHEAR AND DRY AIR ENTRAINMENT.  AN AIR FORCE RESERVE HURRICANE
HUNTER AIRCRAFT MEASURED 850 MB FLIGHT-LEVEL WINDS OF 61 KT...WITH
RELIABLE-LOOKING SFMR WINDS OF 45-50 KT.    BASED ON THIS AND
SIMILAR DOPPLER RADAR WINDS...THE INITIAL INTENSITY IS INCREASED TO
50 KT.  THE LATEST MINIMUM PRESSURE REPORTED BY THE HURRICANE
HUNTER IS 1003 MB.

FAY HAS BEEN MOVING IN FITS AND STARTS FOR THE PAST COUPLE OF
DAYS...WITH THE CENTER MOVING FASTER TOWARD THE NORTH-NORTHWEST
DURING THE PAST 6 HR.  THE INITIAL MOTION IS 335/11.  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.  MOST OF THE TRACK GUIDANCE
RESPONDS TO THIS EVOLUTION BY FORECASTING FAY TO MOVE GENERALLY
NORTHWARD NEAR OR OVER THE FLORIDA PENINSULA AND INTO THE EASTERN
UNITED STATES.  HOWEVER...THE GFS AND ECMWF BOTH FORECAST FAY TO
TURN NORTHEASTWARD INTO THE ATLANTIC AND STALL BY 120 HR...WHILE
THE NOGAPS CONTINUES TO CALL FOR A MORE WESTERLY MOTION TOWARD THE
FLORIDA PANHANDLE.  THE HYDROMETEOROLOGICAL PREDICTION CENTER NOTED
THAT THE GFS AND ECMWF ENSEMBLES ARE NOT IN GOOD AGREEMENT WITH THE
OPERATIONAL RUNS...SO THESE OUTLIERS ARE IGNORED FOR THE MOMENT.
THE NEW FORECAST TRACK WILL FOLLOW THE NORTHWARD SCENARIO...LYING
JUST A LITTLE TO THE EAST OF THE CONSENSUS MODELS AND THE CENTER OF
THE GUIDANCE ENVELOPE.  THE TRACK BRINGS THE CENTER OVER THE
SOUTHWESTERN COAST OF FLORIDA IN A LITTLE OVER 24 HR.

FAY IS IN A MODERATE SOUTHWESTERLY VERTICAL SHEAR ENVIRONMENT...AND
THE UPPER-LEVEL WINDS WILL LIKELY REMAIN LESS THAN IDEAL FOR THE
NEXT 24-48 HR.  THIS...COMBINED WITH THE DRY AIR AND THE CURRENT
STRUCTURE...WILL LIKELY PREVENT RAPID INTENSIFICATION.  HOWEVER...
THE GUIDANCE SHOWS GRADUAL STRENGTHENING...WITH THE GFDL AND HWRF
MODELS MAKING FAY A HURRICANE BEFORE LANDFALL.  THUS...THE
INTENSITY FORECAST WILL FOLLOW SUIT.  AFTER LANDFALL...FAY SHOULD
SLOWLY WEAKEN AND BECOME A REMNANT LOW BY 120 HR.  THIS INTENSITY
FORECAST IS LOW CONFIDENCE...AND THERE IS A DISTINCT CHANCE FAY
MIGHT NOT REACH HURRICANE STRENGTH BEFORE LANDFALL...ESPECIALLY IF
IT MOVES TO THE RIGHT OF THE FORECAST TRACK.

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.

FORECAST POSITIONS AND MAX WINDS

INITIAL      18/1500Z 23.6N  81.5W    50 KT
 12HR VT     19/0000Z 24.6N  81.8W    55 KT
 24HR VT     19/1200Z 26.2N  82.1W    65 KT
 36HR VT     20/0000Z 27.8N  82.0W    50 KT...INLAND
 48HR VT     20/1200Z 29.3N  81.8W    40 KT...INLAND
 72HR VT     21/1200Z 31.5N  81.5W    35 KT...INLAND
 96HR VT     22/1200Z 33.6N  81.5W    25 KT...INLAND
120HR VT     23/1200Z 35.5N  82.5W    20 KT...INLAND REMNANT LOW

$$
FORECASTER BEVEN



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