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TROPICAL DEPRESSION TWELVE DISCUSSION NUMBER  10
NATIONAL WEATHER SERVICE MIAMI FL
5 AM EDT FRI OCT 08 1999
 
THE CONVECTIVE ACTIVITY ASSOCIATED WITH TROPICAL DEPRESSION TWELVE
REMAINS SPARSE...POORLY ORGANIZED AND WELL-REMOVED FROM THE CENTER.
THE INITIAL INTENSITY WILL BE HELD AT 30 KT.
 
THE MULTICHANNEL GOES-8 IMAGERY SUGGESTS THAT THE CENTER OF THE
DEPRESSION IS NOT VERY WELL-DEFINED. THE INITIAL MOTION ESTIMATE
IS 300/3.  THE SYSTEM IS DRIFTING WEST-NORTHWEST AROUND THE WESTERN
PERIPHERY OF THE LOW-LEVEL SUBTROPICAL RIDGE.  THE OFFICIAL FORECAST
CONTINUES THIS GENERAL MOTION THROUGH 72 HRS WITH A GRADUAL INCREASE
IN FORWARD SPEED AFTER 36 HRS.  THIS FORECAST IS IN GOOD AGREEMENT
WITH BAMS...ALTHOUGH SLIGHTLY SLOWER...AND IS VERY SIMILAR TO THE
PREVIOUS ADVISORY.
 
THE SYSTEM CONTINUES TO FEEL THE NEGATIVE INFLUENCE OF WESTERLY/
SOUTHWESTERLY VERTICAL WIND SHEAR ASSOCIATED WITH THE STRONG 
UPPER-LEVEL TROUGH/LOW SEEN IN WATER VAPOR IMAGERY NORTH OF THE
DEPRESSION.  THE SHEAR HAS BEEN PERSISTENT CONTRARY TO THE FORECASTS
BY THE GLOBAL MODELS. IN FACT...THE TROUGH HAS SHIFTED SOUTHWARD
OVER THE LAST 24 HRS.  BOTH THE AVN AND NOGAPS MODELS CONTINUE TO
INDICATE THAT THE TROUGH WILL WEAKEN AND SHIFT EASTWARD WITHIN 
24 HRS OR SO THEREBY LESSENING THE SHEAR. CURRENT SATELLITE TRENDS
SUGGEST THAT THIS MAY NOT OCCUR AS QUICKLY AS FORECAST. FURTHERMORE
...THE OUTFLOW ASSOCIATED WITH THE APPROACHING TROPICAL WAVE NEAR
33W/34W WILL LIKELY INCREASE THE SHEAR OVER THE CYCLONE. SO... UNTIL
THERE ARE SIGNS OF THE SHEAR ABATING...THE SYSTEM WILL BE MAINTAINED
AS A DEPRESSION THROUGH 72 HRS.
 
DESPITE THE LARGE NATURE OF THE CIRCULATION THE HOSTILE ENVIRONMENT
MAY PERSIST LONG ENOUGH THAT THE SYSTEM MAY NOT RECOVER AND COULD
WEAKEN OR DISSIPATE BEFORE THE END OF THE FORECAST PERIOD...PERHAPS
WITHIN 24 HRS OR SO.
 
GUINEY
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL     08/0900Z 16.6N  47.8W    30 KTS
12HR VT     08/1800Z 16.8N  48.3W    30 KTS
24HR VT     09/0600Z 17.2N  48.9W    30 KTS
36HR VT     09/1800Z 17.5N  49.5W    30 KTS
48HR VT     10/0600Z 18.0N  50.5W    30 KTS
72HR VT     11/0600Z 19.5N  53.0W    30 KTS
 
 
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