11:00pm Forecast Discussion 8/18/08

FAY'S ORGANIZATION HAS WAXED AND WANED THIS EVENING. THE STORM
BECAME QUITE DISORGANIZED IN APPEARANCE ON WSR-88D RADAR
OBSERVATIONS FROM KEY WEST AND MIAMI EARLIER THIS EVENING...AND THEN
SHOWED INCREASED SPIRAL BANDING BUT NO CLOSED EYEWALL STRUCTURE.
AIR FORCE HURRICANE HUNTER OBSERVATIONS SHOWED A FALL IN CENTRAL
PRESSURE BUT NO INCREASE IN FLIGHT-LEVEL WINDS YET. THE TROPICAL
CYCLONE IS EMBEDDED IN A DIFFLUENT UPPER-LEVEL FLOW ENVIRONMENT ON
THE EAST SIDE OF A SHORT WAVE TROUGH OR CYCLONIC SHEAR AXIS AND
THIS ENVIRONMENT IS ALSO IMPARTING MODEST SOUTHWESTERLY SHEAR OVER
FAY. NONETHELESS...THERE IS STILL A CHANCE FOR FAY TO STRENGTHEN
INTO A HURRICANE PRIOR TO CROSSING THE COAST TUESDAY MORNING. OUR
FORECAST FOR FAY'S WEAKENING OVER THE PENINSULA MORE OR LESS
FOLLOWS THE DECAY SHIPS MODEL.

AIRCRAFT AND RADAR FIXES YIELD AN INITIAL MOTION NEAR 360/8. FAY IS
MOVING BETWEEN A MID-LEVEL ANTICYCLONE TO ITS EAST AND A MID- TO
UPPER-LEVEL TROUGH TO ITS WEST AND NORTHWEST. SOME OF THE
DYNAMICAL TRACK GUIDANCE...SUCH AS THE GFDL...HWRF...AND U.K. MET
OFFICE MODELS...HAVE SHIFTED A LITTLE TO THE EAST FOR FAY'S TREK
ACROSS THE FLORIDA PENINSULA...SO THE OFFICIAL FORECAST WAS ALSO
ADJUSTED SLIGHTLY TO THE RIGHT. AFTER 1-2 DAYS...GLOBAL MODELS
INDICATE THAT THE STEERING PATTERN WILL BREAK DOWN AS A
MID-TROPOSPHERIC RIDGE BUILDS OVER THE EASTERN U.S. AND BLOCKS THE
FORWARD PROGRESS OF THE TROPICAL CYCLONE. THERE IS GREAT DIVERSITY
IN THE OBJECTIVE TRACK FORECASTS FOR THE LATTER HALF OF THE
PERIOD...AND THEREFORE LARGER THAN USUAL UNCERTAINTY AS TO WHERE
FAY WILL EVENTUALLY GO. THE OFFICIAL TRACK FORECAST IS ROUGHLY IN
THE MIDDLE OF THE HIGHLY SPREAD MODEL TRACKS. THE FORECAST OF
FAY'S INTENSITY IN THE 72-120 HOUR TIME FRAME IS OF COURSE HIGHLY
DEPENDENT ON HOW MUCH THE SYSTEM MOVES OVER WATER. SHOULD FAY
REMAIN VERY NEAR OR OVER LAND...IT WOULD PROBABLY WEAKEN TO
DISSIPATION SOONER THAN SHOWN HERE.