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TROPICAL DEPRESSION TEN DISCUSSION NUMBER   3
NATIONAL WEATHER SERVICE MIAMI FL
5 AM EDT SUN SEP 15 2002
 
RECENT SATELLITE IMAGES AFTER COMING OUT OF THE SATELLITE ECLIPSE 
MODE INDICATE FAIRLY WELL-ORGANIZED LOW-LEVEL AND MID-LEVEL CLOUD 
FIELDS. ALSO...A SMALL OF BURST OF DEEP CONVECTION HAS DEVELOPED 
JUST NORTH OF THE ALLEGED CENTER. THE EXACT LOCATION OF THE 
LOW-LEVEL CENTER IS DIFFICULT TO ASCERTAIN...BUT I HAVE BASICALLY 
USED EXTRAPOLATION FROM THE PREVIOUS FORECAST AND TRIED TO MAINTAIN 
CONTINUITY WITH A CONSERVATIVE SATELLITE FEATURE THAT CORRELATED 
WITH THE LAST TWO RECON POSITIONS. THE INTENSITY OF 25 KT IS ALSO 
MAINTAINED FROM THE PREVIOUS ADVISORY. AIR FORCE RECON WILL 
INVESTIGATE THE SYSTEM LATER THIS MORNING AND PROVIDE BETTER 
INTENSITY INFORMATION...AND THIS SYSTEM COULD REACH MINIMAL TROPICAL 
STORM STRENGTH AS IT PASSES OVER OR NEAR THE NETHERLANDS ANTILLES 
LATER THIS AFTERNOON.
 
THE INITIAL MOTION ESTIMATE IS 285/18. THE LAST FEW SATELLITE IMAGES 
SUGGEST THAT THE DEPRESSION HAS MOVED BACK OVER WATER AND HAS ALSO 
TURNED MORE TOWARD THE WEST-NORTHWEST. THE BIGGEST CHANGE SINCE THE 
LAST ADVISORY HAS BEEN THE WESTWARD SHIFT BY ALL OF THE NHC MODEL 
GUIDANCE. IN FACT...THE PREVIOUS FORECAST TRACK NOW LIES WELL 
OUTSIDE THE EASTERNMOST EDGE OF THE MODEL ENVELOPE. AS SUCH...THE 
OFFICIAL TRACK FOR THIS ADVISORY WAS SHIFTED WESTWARD AND NOW TAKES 
THE CYCLONE ALONG THE WEST COAST...INSTEAD OF THE EAST COAST...OF 
JAMAICA IN 48 TO 72 HOURS. EXCLUDING THE CLIMATOLOGICAL MODELS... 
THERE IS MUCH BETTER CONVERGENCE OF THE DYNAMICAL MODELS AS FAR AS 
DIRECTION IS CONCERNED. THE UKMET MODEL KEEPS THE DEPRESSION WEAK OR 
NON-EXISTENT FOR ABOUT 36 HOURS...WHICH RESULTS IN A MORE NORTHWARD 
TRACK TO THE EAST OF JAMAICA. HOWEVER...NOGAPS...AVN...THE AVN 
ENSEMBLE...AND GFDL MODELS ARE VERY SIMILAR WITH THE DIRECTION 
THROUGH 72 HOURS. THE GFDL APPEARS TO BE TOO FAST BY VIRTUE OF ITS 
ROBUST DEEPENING...WHEREAS THE NOGAPS AND AVN MODELS ARE VERY 
SIMILAR. THE OFFICIAL TRACK IS CLOSE TO THE GFDL...NOGAPS...AND AVN 
CONSENSUS FOR TRACK DIRECTION...BUT THE SPEED OF THE AVN AND AVN 
ENSEMBLE MODELS WAS USED.

THE INTENSITY FORECAST IS A LITTLE UNNERVING GIVEN THE TIME OF YEAR
AND THE PRIME OCEAN AND ENVIRONMENTAL CONDITIONS THAT LIE AHEAD.
THE SHIPS INTENSITY MDOEL ONLY BRINGS THE CYCLONE UP TO 66 KT IN 72
HOURS DUE TO NORTHERLY SHEAR INCREASING TO MORE THAN 20 KT.
HOWEVER... THAT FORECAST IS BASED ON THE PREVIOUS TRACK BEING EAST
OF JAMAICA WHICH WOULD PUT IT CLOSER TO THE STRONG DIGGING JET
FORECAST TO DEVELOP ON THE WEST SIDE OF A TROUGH THAT WILL BE
ACROSS THE NORTHEAST LESSER ANTILLES AFTER 48 HOURS.  WITH THE TRACK
SHIFTED FARTHER WEST...THE UPPER-LEVEL SHEAR SHOULD BE LESS AND...IN
FACT...THE STRONG DIGGING JET TO THE EAST WOULD ACTUALLY ENHANCE THE
OUTFLOW AND POSSIBLY ALLOW FOR SOME RAPID INTENSIFICATION TO OCCUR.
THEREFORE...THE OFFICIAL INTENSITY FORECAST WAS INCREASED ABOVE
SHIPS...AND IT COULD EVEN END UP BEING ON THE LOW SIDE WHEN ITS ALL 
SAID AND DONE.  IT SHOULD BE NOTED THAT THE GFDL MODEL DOES TEND TO 
PERFORM WELL IN WEAK OR LOW SHEAR CONDITIONS LIKE WHAT THE AVN IS
FORECASTING AFTER 36 HOURS...AND THE GFDL BRINGS THIS SYSTEM TO 955
MB AND 112 KT IN 72 HOURS.

FORECASTER STEWART
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL     15/0900Z 10.7N  65.1W    25 KTS
12HR VT     15/1800Z 11.8N  67.9W    30 KTS
24HR VT     16/0600Z 13.4N  71.5W    40 KTS
36HR VT     16/1800Z 15.2N  74.6W    50 KTS
48HR VT     17/0600Z 16.9N  77.1W    60 KTS
72HR VT     18/0600Z 19.5N  80.0W    75 KTS
 
 
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