[Tropical] Tropical Cyclone Discussion

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WTNT41 KNHC 230858
TCDAT1
TROPICAL STORM FAY DISCUSSION NUMBER  31
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL062008
500 AM EDT SAT AUG 23 2008

RADAR AND SURFACE DATA INDICATE THAT THE CENTER OF FAY MADE LANDFALL
ABOUT 0600 UTC JUST SOUTHWEST OF CARRABELLE FLORIDA.  THE LATEST
IMAGERY FROM THE WSR-88D IN TALLAHASSEE SHOWS A DECREASE IN
CONVECTION NEAR THE CENTER...AND AN INCREASE ON CONVECTION BANDING
AWAY FROM THE CENTER IN THE EASTERN SEMICIRCLE.  THERE ARE NO
RECENT OBSERVATIONS OF SUSTAINED TROPICAL-STORM FORCE WINDS FROM
EITHER LAND OR MARINE STATIONS...SO THE INTENSITY IS A LITTLE
UNCERTAIN.  BASED MAINLY ON DOPPLER WIND VELOCITIES...THE INITIAL
INTENSITY IS DECREASED TO 40 KT.  IT SHOULD BE NOTED THAT DOPPLER
WINDS OF NEAR 65 KT HAVE BEEN OBSERVED OVER LAND TO THE NORTH OF
THE CENTER...BUT SURFACE OBSERVATIONS SUGGEST THESE WINDS ARE NOT
MIXING DOWN TO THE SURFACE AT THIS TIME.

THE INITIAL MOTION IS A SOMEWHAT ERRATIC 275/6...AS THE CENTER
OCCASIONALLY SURGES AHEAD FOLLOWED BY PERIODS OF LITTLE MOVEMENT.
FAY REMAINS SOUTH OF A LOW/MID-LEVEL RIDGE OVER THE EASTERN UNITED
STATES.  THE LARGE-SCALE MODELS SUGGEST THIS RIDGE SHOULD WEAKEN
AFTER 24-48 HR AS A DEEP-LAYER TROUGH MOVES THROUGH THE NORTHERN
UNITED STATES.  AT THE SAME TIME...A LOW/MID-LEVEL RIDGE IS
FORECAST TO DEVELOP NEAR OR OVER THE FLORIDA PENINSULA.  THIS
EVOLUTION SHOULD STEER FAY WESTWARD FOR 48-72 HR...THEN STEER THE
CYCLONE SLOWLY NORTHEASTWARD.  WHILE THE TRACK GUIDANCE GENERALLY
AGREES WITH THIS SCENARIO...AFTER 48 HR THERE IS A CONSIDERABLE
SPREAD IN THE SPEED OF THE NORTHEAST MOVEMENT.  THE GFS AND ECMWF
ARE THE FASTEST WITH THIS MOTION...WHILE THE HWRF...WHICH FORECASTS
FAY TO MAKE A LOOP OVER SOUTHEASTERN LOUISIANA...IS THE SLOWEST.
THE NEW FORECAST TRACK IS AN UPDATE OF THE PREVIOUS TRACK THROUGH
72 HR...THEN CALLS FOR A MOTION SLIGHTLY FASTER AND TO THE RIGHT OF
THE PREVIOUS FORECAST.  THE LATTER PART OF THE FORECAST IS ON THE
LEFT SIDE OF THE GUIDANCE ENVELOPE AND SLOWER THAN THE MODEL
CONSENSUS.

FAY WILL REMAIN IN A GENERALLY FAVORABLE UPPER-LEVEL WIND
ENVIRONMENT FOR THE NEXT 48-72 HR...SO THE INTENSITY WILL BE
CONTROLLED MAINLY BY HOW MUCH LAND THE STORM ENCOUNTERS.  ON THE
FORECAST TRACK...ENOUGH OF THE CIRCULATION WILL BE OVER WATER FOR
THE NEXT 72 HR TO MAINTAIN FAY AS A TROPICAL STORM...AND THIS IS
REFLECTED IN THE INTENSITY FORECAST.  THERE IS A CHANCE THE STORM
COULD BE STRONGER THAN FORECAST IF IT GOES SOUTH OF THE FORECAST
TRACK.  AFTER 72 HR...FAY SHOULD BE FAR ENOUGH INLAND AND IN ENOUGH
VERTICAL WIND SHEAR TO CAUSE IT TO DECAY TO A REMNANT LOW.

REGARDLESS OF ITS EXACT TRACK...FAY WILL BE MOVING RATHER SLOWLY
DURING THE NEXT SEVERAL DAYS...POSING A SIGNIFICANT HEAVY RAINFALL
AND FLOOD HAZARD TO A VERY LARGE AREA.

FORECAST POSITIONS AND MAX WINDS

INITIAL      23/0900Z 29.9N  84.9W    40 KT...INLAND
 12HR VT     23/1800Z 30.0N  86.0W    40 KT...OVER WATER
 24HR VT     24/0600Z 30.3N  87.5W    40 KT...INLAND
 36HR VT     24/1800Z 30.5N  89.1W    40 KT...INLAND
 48HR VT     25/0600Z 30.5N  90.4W    35 KT...INLAND
 72HR VT     26/0600Z 30.5N  91.0W    30 KT...INLAND
 96HR VT     27/0600Z 32.1N  90.5W    25 KT...INLAND
120HR VT     28/0600Z 33.5N  89.5W    20 KT...INLAND REMNANT LOW

$$
FORECASTER BEVEN



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