HOME	ACTIVE CYCLONES	FORECASTS	IMAGERY	ABOUT TPC	RECONNAISSANCE

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TROPICAL STORM DENNIS DISCUSSION NUMBER  37
NATIONAL WEATHER SERVICE MIAMI FL
11 PM EDT WED SEP 01 1999
 
A CONVECTIVE BAND FLARED UP WEST OF THE CENTER OF DENNIS DURING
THE EVENING AND THEN WRAPPED AROUND THE SOUTH SIDE. THIS PULLED THE
CENTER A LITTLE EASTWARD. THE BAND HAS SINCE WEAKENED...WITH RADAR
AND SATELLITE CURRENTLY INDICATING LITTLE CONVECTION NEAR THE
CENTER. BASED ON THIS...AND PERIPHERAL OBSERVATIONS...THE MAXIMUM
SUSTAINED WINDS REMAIN AT 50 KT.

GIVE THIS EASTWARD WOBBLE...THE INITIAL MOTION FOR THIS PACKAGE IS
STATIONARY. MODEL GUIDANCE HAS SOMEWHAT CLUSTERED INTO TWO
POSSIBILITIES. THE FIRST...SUPPORTED BY THE BAMS...BAMM...AND
NHC98UK...IS FOR A GENERAL WESTWARD MOTION INTO NORTH CAROLINA IN
RESPONSE TO THE LOW LEVEL RIDGE NEAR DENNIS SHIFTING TO THE EAST.
THE SECOND...SUPPORTED BY THE AVN...NOGAPS...AND GFDL...IS FOR A
MORE SOUTHWESTWARD MOTION IN RESPONSE TO A BUILDING MID LEVEL RIDGE
OVER THE CENTRAL AND EASTERN U.S.. EXAMINATION OF SURFACE ANALYSES
AND WATER VAPOR IMAGERY INDICATES BOTH OF THESE RIDGES MAY BE
DEVELOPING AS FORECAST. THUS...THE OFFICIAL FORECAST IS A COMPROMISE
BETWEEN THE TWO EXTREMES AND AN UPDATE OF THE PREVIOUS FORECAST. 

THERE ARE SO MANY FACTORS INVOLVED IN THE INTENSITY FORECAST THAT IT
IS HARD TO KNOW WHERE TO BEGIN. FIRST...AS MENTIONED EARLIER...
DENNIS MAY BE GOING THROUGH A SUBTROPICAL PHASE. THIS WOULD DELAY
STRENGTHENING THROUGH TROPICAL CYCLONE PROCESSES. SECOND...VERTICAL
SHEAR HAS DECREASED SINCE YESTERDAY...WITH SOME INDICATIONS OF
ANTICYCLONIC OUTFLOW. HOWEVER...WESTERLY SHEAR...WELL FORECAST BY
THE MODELS...INCREASES TO THE SOUTHWEST ALONG THE FORECAST TRACK.
THIRD...AN UPPER LEVEL TROUGH...POORLY INITIALIZED IN THE MODELS...
IS SEEN IN WATER VAPOR APPROACHING DENNIS FROM THE WEST. THIS MIGHT
EITHER INCREASE CONVECTION OR INCREASE SHEAR. FOURTH...DENNIS HAS
BEEN ESSENTIALLY STATIONARY FOR 36 TO 48 HOURS...AND HAS LIKELY
COOLED OFF THE OCEAN UNDERNEATH IT. THIS WOULD HAMPER
INTENSIFICATION...ALTHOUGH SOMEWHAT WARMER SSTS ARE PRESENT TO THE
SOUTHWEST ALONG THE FORECAST TRACK...ESPECIALLY OVER THE GULF
STREAM. GIVEN ALL THESE UNCERTAINTIES...THE INTENSITY FORECAST HOLDS
DENNIS AT ITS CURRENT STRENGTH THROUGH 72 HOURS.

BEVEN
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL     02/0300Z 35.3N  73.6W    50 KTS
12HR VT     02/1200Z 35.3N  74.1W    50 KTS
24HR VT     03/0000Z 35.1N  75.0W    50 KTS
36HR VT     03/1200Z 34.9N  75.7W    50 KTS
48HR VT     04/0000Z 34.5N  76.5W    50 KTS
72HR VT     05/0000Z 33.5N  78.0W    50 KTS
 
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