[Tropical] Tropical Cyclone Discussion

[EMWIN Server]

WTNT41 KNHC 182104
TCDAT1
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



This weather bulletin was brought to you by:
www.nashvilleweather.net