HOME	ACTIVE CYCLONES	FORECASTS	IMAGERY	ABOUT TPC	RECONNAISSANCE

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TROPICAL STORM DENNIS DISCUSSION NUMBER  43
NATIONAL WEATHER SERVICE MIAMI FL
11 AM EDT FRI SEP 03 1999
 
DENNIS LOOKS BETTER ORGANIZED THIS MORNING. ALTHOUGH CONVECTIVE TOPS
ARE RELATIVELY LOW...BANDING HAS INCREASED AROUND THE CENTER IN
BOTH SATELLITE IMAGERY AND WSR-88D DATA FROM MOREHEAD CITY.
SATELLITE INTENSITY ESTIMATES FROM TAFB AND SAB ARE 45 KT AND 35 KT
RESPECTIVELY. THE MAXIMUM SUSTAINED WINDS WILL REMAIN AT 50 KT FOR
THIS ADVISORY. AN AIR FORCE RESERVE HURRICANE HUNTER WILL ARRIVE IN
DENNIS AROUND 18Z TO UPDATE THE CURRENT INTENSITY AND WIND RADII.

DENNIS HAS MOVED 180/05 FOR THE PAST 12 HOURS. HOWEVER...RECENT
SATELLITE AND RADAR IMAGERY SUGGESTS A SLOWER MOTION...SO 180/03
WILL BE USED IN THIS PACKAGE. WATER VAPOR IMAGERY INDICATES THE
STORM IS EMBEDDED IN A LARGE SCALE CYCLONIC CIRCULATION...WITH
MID/UPPER LEVEL RIDGING WEST OF THE STORM OVER THE EASTERN U.S..
LARGE SCALE MODELS AGREE THAT THE RIDGE WILL WEAKEN AFTER 24 HOURS
AS A LARGE TROUGH OVER THE WESTERN U.S. MOVES EASTWARD. THE GUIDANCE
RESPONDS TO THESE CHANGES IN THE FLOW BY TURNING DENNIS TO EITHER A
NORTHWEST OR NORTHERLY TRACK DURING THE FORECAST PERIOD. THE
NORTHWEST OPTION IS SUPPORTED BY THE GFDL...NOGAPS...UKMET...
ECMWF...AND ETA MODELS...WHILE THE NORTH OPTION IS SUPPORTED BY THE
AVN...NHC98UK...AND THE BAM MODELS. THE OFFICIAL FORECAST TRACK GOES
WITH THE NORTHWEST OPTION...ALTHOUGH IT IS SHIFTED SOUTH OF THE
PREVIOUS PACKAGE EARLY IN THE FORECAST AND NORTH OF IT LATER. THE
CURRENT FORECAST CALLS FOR LANDFALL IN 48 TO 60 HOURS.
 
WHILE THE OVERALL UPPER LEVEL ENVIRONMENT AROUND DENNIS IS
CYCLONIC...AN SMALL ANTICYCLONE IS FORMING OVER THE CENTER. LARGE
SCALE MODEL GUIDANCE INDICATES THAT STRONG WESTERLIES JUST SOUTHWEST
OF THE CYCLONE SHOULD GRADUALLY DIMINISH DURING THE FORECAST PERIOD
AS A SHORTWAVE TROUGH PRECEDING THE LARGE WESTERN U.S. TROUGH
APPROACHES. THIS COULD CREATE A MORE FAVORABLE ENVIRONMENT FOR
INTENSIFICATION. A LIMITING FACTOR...HOWEVER...IS SSTS. SHIP AND
BUOY DATA INDICATE THAT TEMPERATURES ALONG THE FORECAST TRACK ARE
26C OUTSIDE THE GULF STREAM..COMPARED TO 28C-29C A FEW DAYS AGO.
THIS MAY SLOW INTENSIFICATION. THE INTENSITY FORECAST CALLS FOR
LITTLE CHANGE IN STRENGTH UNTIL 48 HOURS...WHEN DENNIS WILL BE
PASSING OVER THE GULF STREAM.
 
BEVEN
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL     03/1500Z 33.0N  74.0W    50 KTS
12HR VT     04/0000Z 32.9N  74.0W    50 KTS
24HR VT     04/1200Z 32.9N  74.8W    50 KTS
36HR VT     05/0000Z 33.2N  75.6W    50 KTS
48HR VT     05/1200Z 34.0N  76.5W    55 KTS
72HR VT     06/1200Z 36.0N  78.0W    35 KTS...INLAND

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