[Tropical] Tropical Cyclone Discussion

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WTNT41 KNHC 172105
TCDAT1
TROPICAL STORM FAY DISCUSSION NUMBER   9
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL062008
500 PM EDT SUN AUG 17 2008

FAY HAS BECOME A LITTLE BETTER ORGANZIED IN SATELLITE AND RADAR
IMAGERY THIS AFTERNOON...WITH INCREASED CURVED BANDS OF CONVECTION
NEAR THE CENTER IN THE NORTHEASTERN SEMICIRCLE.  HOWEVER...THERE
ARE SINGS OF SOUTHWESTERLY VERTICAL WIND SHEAR AND DRY AIR
ENTRAINMENT IN THE WESTERN SEMICIRCLE...WHERE THERE IS LITTLE IN
THE WAY OF ORGANIZED CONVECTION OR STRONG WINDS.  AN AIR FORCE
RESERVE HURRICANE HUNTER AIRCRAFT RECENTLY REPORTED A CENTRAL
PRESSURE OF 1003 MB...ALTHOUGH THE PLANE HAS NOT YET SAMPLED THE
WINDS IN THE NORTHEASTERN QUADRANT.  THE INITIAL INTENSITY REMAINS
45 KT BASED ON CONTINUITY AND A 45 KT SATELLITE INTENSITY ESTIMATE
FROM TAFB.

THE CENTER OF FAY SURGED TOWARD THE WEST-NORTHWEST DURING THE
DAY...AT ONE TIME MOVING BETWEEN 18-20 KT.  THAT MOTION APPEARS TO
HAVE ENDED...AND THE INITIAL MOTION FOR THIS ADVISORY IS A SOMEWHAT
UNCERTAIN 300/13.  FAY IS APPROACHING A DEVELOPING WEAKNESS IN A
LOW/MID LEVEL RIDGE OVER THE GULF OF MEXICO...WHICH IS DEVELOPING
DUE TO A MID/UPPER-LEVEL TROUGH OVER THE SOUTHERN UNITED STATES.
THIS PATTERN SHOULD ALLOW FAY TO TURN MORE NORTHWARD AFTER 24 HR...
BUT THERE REMAINS SIGNIFICANT DISAGREEMENT BETWEEN THE MODELS ON
HOW MUCH OF A TURN WILL OCCUR.  THE ECMWF AND CANADIAN MODELS
CONTINUE TO FORECAST A SHARPER TURN WITH LANDFALL IN SOUTHWESTERN
FLORIDA...WITH THE ECMWF SHOWING FAY CROSSING TO THE ATLANTIC THEN
MOVING WESTWARD TO HIT FLORIDA AGAIN.  THE GFS AND GFDL HAVE
SHIFTED WEST SINCE THEIR PREVIOUS RUNS...WHILE THE UKMET HAS
SHIFTED A LITTLE TO THE EAST.  THESE MODELS HAVE JOINED THE HWRF IN
CALLING FOR A TRACK NEAR OR JUST OVER THE WEST COAST OF THE FLORIDA
PENINSULA.  THE NOGAPS CONTINUES TO FORECAST A NORTH-NORTHWESTWARD
MOTION TOWARD THE FLORIDA PANHANDLE.  OVERALL...THE GUIDANCE
ENVELOPE HAS SHIFTED TO THE WEST SINCE THE PREVIOUS PACKAGE...
POSSIBLY DUE TO THE CHANGE IN THE INITIAL POSITION CAUSED BY THE
MOTION SURGE.  THE FORECAST TRACK IS SHIFTED ABOUT 60 N MI TO THE
WEST OF THE PREVIOUS PACKAGE...BUT LIES TO THE EAST OF THE CENTER
OF THE GUIDANCE ENVELOPE AND THE CONSENSUS MODELS.  THE NEW TRACK
IS IN BEST AGREEMENT WITH THE HWRF.

THE INTENSITY FORECAST REMAINS PROBLEMATIC.  THE SHIPS MODEL NOW
FORECASTS PERSISTENT WIND SHEAR DURING THE FORECAST PERIOD...WITH
PERHAPS A PERIOD OF LIGHTER SHEAR FROM 18-48 HR.  THE LARGE-SCALE
MODELS HAVE A VARIETY OF SOLUTIONS FOR THE CURRENT UPPER-LEVEL
TROUGH WEST OF FAY OVER THE GULF OF MEXICO AND THE CARIBBEAN...WITH
NO CLEAR EVIDENCE AT THIS TIME OF WHICH IS CORRECT.  IT APPEARS THE
SHEAR WILL BE LIGHT ENOUGH TO ALLOW FAY TO GRADUALLY STRENGTHEN AS
SHOWN IN THE GFDL MODEL...AND THE NEW INTENSITY FORECAST THUS CALLS
FOR INTENSIFICATION ALONG THOSE LINES.  IT SHOULD BE NOTED THAT THE
HWRF CALLS FOR FAY TO BECOME A CATEGORY 2 HURRICANE OVER THE
EASTERN GULF OF MEXICO...WHILE THE SHIPS MODEL FORECAST A PEAK JUST
BELOW HURRICANE STRENGTH.

THE FORECAST TRACK SITUATION IS SIMILAR TO THAT OF HURRICANE CHARELY
FROM AUGUST 2004...IN THAT A SMALL CHANGE IN THE TRACK OF THE STORM
COULD MAKE A BIG DIFFERENCE IN THE EVETUAL LANDFALL LOCATION.  THE
NHC WIND SPEED PROBABILITIES PRODUCT SHOWS ABOUT AN EQUAL CHANCE OF
HURRICANE-FORCE WINDS FOR THE ENTIRE WEST COAST OF THE FLORIDA
PENINSULA.

FORECAST POSITIONS AND MAX WINDS

INITIAL      17/2100Z 21.0N  80.2W    45 KT
 12HR VT     18/0600Z 22.3N  81.7W    50 KT...INLAND
 24HR VT     18/1800Z 23.8N  82.8W    55 KT...OVER WATER
 36HR VT     19/0600Z 25.3N  83.1W    65 KT
 48HR VT     19/1800Z 27.0N  83.2W    75 KT
 72HR VT     20/1800Z 30.0N  83.0W    65 KT...INLAND
 96HR VT     21/1800Z 33.5N  82.0W    30 KT...INLAND
120HR VT     22/1800Z 37.0N  82.0W    20 KT...INLAND REMNANT LOW

$$
FORECASTER BEVEN



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