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TROPICAL DEPRESSION FOUR DISCUSSION NUMBER   3
NATIONAL WEATHER SERVICE MIAMI FL
11 PM EDT WED AUG 15 2001

DVORAK SATELLITE INTENSITY ESTIMATES INDICATE THAT THE CYCLONE IS 
VERY NEAR TROPICAL STORM STRENGTH.  A BANDING FEATURE HAS BEEN 
TRYING TO DEVELOP OVER THE NORTHWEST QUADRANT...BUT OVERALL THE 
CONVECTION IS RATHER RAGGED-LOOKING AT THIS TIME.  THE SYSTEM HAS 
BEEN UNDER THE INFLUENCE OF EASTERLY SHEAR...THUS INHIBITING 
UPPER-LEVEL OUTFLOW OVER THE EASTERN SEMICIRCLE.  IT IS ASSUMED THAT 
THE HIGH LEVEL EASTERLIES OVER THE SYSTEM WILL GRADUALLY DECREASE AS 
THE CYCLONE MOVES FARTHER WEST...AND ALLOW FOR GRADUAL 
STRENGTHENING.  THE OFFICIAL INTENSITY FORECAST IS THE SAME AS THE 
PREVIOUS ONE...SIMILAR TO THE LATEST GFDL MODEL RUN BUT NOT AS 
AGRESSIVE AS THE STATISTICAL/DYNAMICAL GUIDANCE MODEL...SHIPS. 

THE RAPID WESTWARD MOVEMENT...270/23...CONTINUES.  THERE IS A VERY 
LARGE AND STRONG DEEP-LAYER ANTICYCLONE SITUATED TO THE NORTH OF THE 
DEPRESSION...FORCING THE SWIFT WESTWARD MOTION.  GLOBAL MODEL 
GUIDANCE INDICATE A CONTINUATION OF THIS STEERING REGIME FOR THE 
NEXT COUPLE OF DAYS...WITH SOME WEAKENING OF THE ANTICYLONE IN THE 
LATTER PART OF THE PERIOD.  HENCE THE OFFICIAL FORECAST SHOWS A 
WESTWARD TO WEST-NORTHWARD MOTION WITH A GRADUAL SLOWING OF THE 
FORWARD SPEED DURING THE NEXT COUPLE OF DAYS.  THIS IS ALSO SIMILAR 
TO THE PREVIOUS OFFICIAL TRACK FORECAST AND IN FAIR AGREEMENT WITH 
THE LATEST GFDL RUN.  THE NCEP GLOBAL MODEL IS A LITTLE TO THE RIGHT 
OF THIS TRACK.  HOWEVER THE LATEST...18Z...RUN OF THAT MODEL SHOWED 
SOME DEFICIENCIES IN THE INITIALIZATION...WITH AN ADDITIONAL 
LOW-LEVEL VORTICITY MAXIMUM TO THE EAST OF THE ACTUAL CENTER.  THE 
FSU SUPERENSEMBLE SHOWS A TRACK SLIGHTLY TO THE SOUTH AND A TAD 
FASTER THAN THE OFFICIAL FORECAST.

A TROPICAL STORM WATCH IS ISSUED FOR SOME OF THE WINDWARD ISLANDS.

FORECASTER PASCH
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL     16/0300Z 12.6N  50.2W    30 KTS
12HR VT     16/1200Z 13.0N  53.0W    40 KTS
24HR VT     17/0000Z 13.5N  57.0W    50 KTS
36HR VT     17/1200Z 14.0N  60.5W    60 KTS
48HR VT     18/0000Z 14.5N  63.0W    70 KTS
72HR VT     19/0000Z 16.0N  67.5W    75 KTS
 
 
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