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TROPICAL STORM DENNIS DISCUSSION NUMBER  40
NATIONAL WEATHER SERVICE MIAMI FL
5 PM EDT THU SEP 02 1999
 
AN OBSERVATION FROM A VESSEL WITH CALL SIGN ELFV3 SHOWED WEST-
NORTHWEST WINDS OF 45 KNOTS ABOUT 50 MILES SOUTHWEST OF THE CENTER.
SINCE IT IS UNLIKELY THAT THIS IS THE HIGHEST WIND SPEED IN
THE CIRCULATION...THE ESTIMATE OF 50 KNOTS FOR THE CURRENT INTENSITY
LOOKS REASONABLE.
 
THE STORM CONTINUES TO APPEAR WELL ORGANIZED ON VISIBLE SATELLITE
IMAGES...BUT OVERALL THE CONVECTION REMAINS QUITE SHALLOW.  WSR-88D
OBSERVATIONS SHOWED THE CENTER BECOMING A LITTLE BETTER-DEFINED THIS
AFTERNOON.  THE SHIPS MODEL FORECASTS 65 KNOTS BY 48 HOURS...BUT
THIS IS A STATISTICAL MODEL BASED MAINLY ON DATA FROM TYPICAL
TROPICAL CYCLONES.  DENNIS...AT THIS STAGE...IS FAIRLY ATYPICAL WITH
SOME SUBTROPICAL-TYPE CHARACTERISTICS.  MOREOVER THE SHIPS OUTPUT
INDICATES DECREASING VERTICAL SHEAR OVER THE SYSTEM...AND THIS MAY
NOT VERIFY.  GIVEN THE UNCERTAINTIES...NO CHANGE IN STRENGTH IS
FORECAST.
 
THE CENTER HAS MOVED GENERALLY SOUTHWESTWARD OVER THE PAST FEW
HOURS.  WHETHER THIS IS ANOTHER IN A SERIES OF MEANDERS/WOBBLES...
OR A DEFINITIVE MOTION THAT WILL PERSIST...ONLY TIME WILL TELL. THE
STEERING ENVIRONMENT DURING THE FORECAST PERIOD IS CHARACTERIZED BY
MID-TROPOSPHERIC RIDGES TO THE NORTH-NORTHEAST AND SOUTHWEST OF
DENNIS...AND THE TROPICAL CYCLONE ITSELF APPEARS TO BE EMBEDDED
WITHIN A LARGER-SCALE CYCLONIC CIRCULATION.  THIS IS A COMPLEX
STEERING PATTERN AND THE OBJECTIVE TRACKS...ALTHOUGH FAIRLY
DIVERSE...ROUGHLY SHOW A SOUTHWEST...THEN WEST...AND THEN NORTHWEST
TRACK DURING THE PERIOD.  THE CURRENT OFFICIAL TRACK FORECAST MOVES
DENNIS IN A SIMILAR FASHION...BUT VERY SLOWLY.

BEAR IN MIND THAT THE 48 TO 72 HOURS FORECAST POINTS
ARE...HISTORICALLY... SUBJECT TO LARGE ERRORS.  
 
PASCH
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL     02/2100Z 34.7N  74.0W    50 KTS
12HR VT     03/0600Z 34.6N  74.3W    50 KTS
24HR VT     03/1800Z 34.4N  74.6W    50 KTS
36HR VT     04/0600Z 34.2N  75.1W    50 KTS
48HR VT     04/1800Z 34.0N  76.0W    50 KTS
72HR VT     05/1800Z 34.5N  78.0W    50 KTS
 
 
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