HOME	ACTIVE CYCLONES	FORECASTS	IMAGERY	ABOUT TPC	RECONNAISSANCE

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TROPICAL STORM DENNIS DISCUSSION NUMBER  33
NATIONAL WEATHER SERVICE MIAMI FL
11 PM EDT TUE AUG 31 1999
 
...CORRECTED HURRICANE TO TROPICAL STORM...

DENNIS CURRENTLY AS MUCH RESEMBLES AN EXTRATROPICAL LOW AS A
TROPICAL CYCLONE...WITH LITTLE SIGNIFICANT CONVECTION NEAR THE
CENTER AND A LARGE RADIUS OF MAXIMUM WIND. THE LATEST REPORTS FROM
AN AIR FORCE RESERVE HURRICANE HUNTER INDICATE A 987 MB CENTRAL
PRESSURE AND MAXIMUM FLIGHT LEVEL WINDS OF 71 KT...DOWN 15 KT FROM
EARLIER TODAY. DENNIS IS THEREFORE DOWNGRADED TO A 60 KT TROPICAL
STORM.

THE INITIAL MOTION IS 270/03. THERE IS LITTLE CHANGE IN THE FORECAST
PHILOSOPHY FROM THE PREVIOUS PACKAGE. WATER VAPOR IMAGERY AND THE
LARGE SCALE MODELS INDICATE A DEVELOPING RIDGE OVER THE CENTRAL AND
EASTERN U.S....WHICH WOULD FAVOR DENNIS MOVING ON A WEST TO
SOUTHWEST TRACK. HOWEVER...EXISTING RIDGING OVER THE SOUTHEASTERN
U.S. COULD EITHER SLOW THIS MOTION OR DEFLECT DENNIS TO THE SOUTH.
NHC HURRICANE GUIDANCE IS SCATTERED BETWEEN THE EXTREMES OF
BAMS...OVER KENTUCKY IN 72 HOURS...AND A98E...SHOWING A SOUTHWARD
MOTION THROUGH 72 HOURS. ONE POTENTIAL PROBLEM WITH THE AVN-BASED
GUIDANCE IS THAT THE MODEL DEVELOPS A SPURIOUS LOOKING VORTEX EAST
OF DENNIS OVER THE NEXT 72 HOURS. THIS MAY PRODUCE A MORE SOUTHWARD
MOTION IN THE GUIDANCE THAN WOULD ACTUALLY OCCUR. THE OFFICIAL
FORECAST IS GENERALLY DOWN THE MIDDLE OF THE GUIDANCE...AND A LITTLE
TO THE WEST OF THE PREVIOUS PACKAGE.

THE INTENSITY FORECAST IS EVEN MORE UNCERTAIN. THE AVN AND NOGAPS
MODELS HAVE A POOR HANDLE ON AN EAST-WEST UPPER LEVEL TROUGH OVER
DENNIS...WHICH IS CAUSING DIFLUENCE OVER THE NORTHERN PART OF THE
CIRCULATION AND SUBSIDENCE OVER THE SOUTHERN PART. BOTH MODELS
FORECAST STRONG SHEAR OVER DENNIS...WHICH IS SUSPECT DUE TO THE POOR
INITIALIZATION. HOWEVER...WITH THE CURRENT LACK OF CONVECTION AND A
TROUGH OVER THE SYSTEM INSTEAD OF A RIDGE...A GRADUAL WEAKENING IS
FORECAST THROUGH 36 HOURS. AFTER THAT TIME...WARMER SSTS MAY HELP
HOLD THE INTENSITY UP.

ALTHOUGH THE INTENSITY FORECAST CALLS FOR WEAKENING...ANY SHORT TERM
INCREASE IN THE CONVECTION COULD BRING THE SYSTEM BACK TO HURRICANE
STRENGTH. THEREFORE...THE HURRICANE WATCH WILL REMAIN IN EFFECT
UNTIL A DEFINITIVE WEAKENING TREND IS ESTABLISHED.

BEVEN
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL     01/0300Z 35.2N  73.7W    60 KTS
12HR VT     01/1200Z 35.2N  74.3W    60 KTS
24HR VT     02/0000Z 35.1N  75.1W    55 KTS
36HR VT     02/1200Z 35.0N  75.8W    50 KTS
48HR VT     03/0000Z 34.5N  76.5W    50 KTS
72HR VT     04/0000Z 33.5N  77.5W    50 KTS
 
 
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