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TROPICAL DEPRESSION FOUR DISCUSSION NUMBER   4
NATIONAL WEATHER SERVICE MIAMI FL
5 AM AST THU AUG 16 2001

CONVECTION ASSOCIATED WITH TROPICAL DEPRESSION FOUR HAS INCREASED IN
BOTH COVERAGE AND INTENSITY OVER THE PAST FEW HOURS.  SATELLITE
INTENSITY ESTIMATES FROM TAFB...SAB...AND AFWA ARE 35 KT...30 KT...
AND 25 KT RESPECTIVELY.  BASED ON THIS AND THE RAPID WESTWARD
MOTION...THE SYSTEM MAY WELL BE A TROPICAL STORM NOW.  HOWEVER...
GIVEN THE USUAL NIGHTTIME UNCERTAINTIES ABOUT WHERE THE CENTER IS
IN RELATION TO THE CONVECTION...THE SYSTEM WILL REMAIN A 
DEPRESSION ON THIS PACKAGE.

THE RAPID WESTWARD TRACK CONTINUES AT 270/24.  THERE IS LITTLE
CHANGE IN THE SYNOPTIC REASONING FROM THE PREVIOUS ADVISORY...AS
A LARGE AND STRONG DEEP-LAYER RIDGE CONTINUES NORTH OF THE CYCLONE.
LARGE-SCALE MODELS SHOW ONLY SLIGHT WEAKENING OF THE RIDGE DURING 
THE FORECAST PERIOD...WHICH FAVORS A WEST TO WEST-NORTHWEST MOTION
AT A QUICK FORWARD SPEED.  ALL NHC HURRICANE GUIDANCE FOLLOWS THIS
SCENARIO...ALTHOUGH THERE IS SOME SPREAD AS TO HOW FAR NORTH THE
CYCLONE MAY MOVE.  THE OFFICIAL FORECAST IS SIMILAR TO BUT FASTER
THAN THE PREVIOUS PACKAGE.  IT IS NOTABLE THAT THE MODELS WITH THE
BEST INITIALIZATION OF THE CYCLONE...THE NOGAPS...GFDN...AND GFDL...
ARE ALL FASTER THAN THE OFFICIAL FORECAST.
 
THE DEPRESSION SHOULD REACH TROPICAL STORM STRENGTH SHORTLY IF IT
HAS NOT DONE SO ALREADY.  IT IS SHOWING GOOD ANTICYCLONIC OUTFLOW...
AND LARGE-SCALE MODELS FORECAST A CONTINUED LIGHT SHEAR ENVIRONMENT
FOR THE NEXT THREE DAYS.  THIS FAVORS STRENGTHENING...AND ALL
INTENSITY FORECAST GUIDANCE REFLECTS THIS.  THE ONLY NEGATIVE
FACTORS ARE CLIMATOLOGICAL.  FIRST...MOST ATLANTIC TROPICAL CYCLONES
MOVING THIS QUICKLY HAVE SOME TROUBLE DEVELOPING.  SECOND...THE
SOUTHEASTERN CARIBBEAN IS GENERALLY NOT A FAVORABLE REGION FOR
TROPICAL CYCLONE DEVELOPMENT.  THE INTENSITY FORECAST IS GOING TO
GO AGAINST CLIMATOLOGY AND CALL FOR THE SYSTEM TO REACH HURRICANE
STRENGTH IN 48 HR IN AGREEMENT WITH THE SHIPS MODEL.
 
A TROPICAL STORM WARNING IS NOW IN EFFECT FOR BARBADOS...ST.
LUCIA...AND ST. VINCENT.  TROPICAL STORM WATCHES ARE EITHER NOW IN
EFFECT OR RECOMMENDED ELSEWHERE FROM THE GRENADINES TO DOMINICA.
 
FORECASTER BEVEN
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL     16/0900Z 12.7N  52.6W    30 KTS
12HR VT     16/1800Z 13.0N  56.1W    40 KTS
24HR VT     17/0600Z 13.6N  60.0W    50 KTS
36HR VT     17/1800Z 14.3N  63.0W    60 KTS
48HR VT     18/0600Z 15.0N  66.0W    70 KTS
72HR VT     19/0600Z 16.5N  71.0W    80 KTS
 
 
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