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TROPICAL STORM DEBBY DISCUSSION NUMBER   9
NATIONAL WEATHER SERVICE MIAMI FL
5 PM EDT MON AUG 21 2000
 
DEBBY REMAINS A SHEARED SYSTEM...MAINLY DUE TO THE LOW-LEVEL
CIRCULATION MOVING FASTER THAN THE MID- AND UPPER-LEVEL
CIRCULATIONS.  AIR FORCE RESERVE RECON FOUND LITTLE CHANGE IN THE
1500 FT WINDS THIS AFTERNOON...SO THE INITIAL INTENSITY IS HELD AT
60 KT.  OUTFLOW IS GOOD IN THE NORTH SEMICIRCLE AND RESTRICTED
ELSEWHERE.
 
THE INITIAL MOTION IS ESTIMATED TO BE 280/19.  THE LOW-LEVEL CENTER
CONTINUES TO REDEVELOP NEAR EACH CONVECTIVE BURST IN THE NORTHEAST
QUADRANT AND THEN MOVES OUT TO THE WEST...SO WE BASICALLY WENT WITH
MIDDLE OF THE CIRCULATION ENVELOPE AND JUST NORTH OF THE RECON
FIXES.  THE SUBTROPICAL RIDGE TO THE NORTH REMAINS INTACT AND SHOULD
HELP TO KEEP DEBBY ON A GENERAL WEST OR SLIGHTLY WEST-NORTHWEST
TRACK THROUGH THE PERIOD.  THE GLOBAL MODELS MAINTAIN A WEAKNESS IN
THE RIDGE OVER THE SOUTHEAST U.S. AND THE BAHAMAS...WHICH SHOULD
SLOW DOWN DEBBY AND ALLOW A GRADUAL TURN MORE TOWARD THE WEST-
NORTHWEST.  THE UKMET MODEL TAKES DEBBY MORE POLEWARD THROUGH THE
BAHAMAS AFTER 48 HOURS...BUT THIS IS THE ONLY MODEL THAT DOES THAT.
THE GFDL MODEL HAS BEEN FLIP-FLOPPING BACK AND FORTH EITHER SIDE OF
OUR PREVIOUS FORECAST TRACKS...SO THE OFFICIAL TRACK IS CLOSE TO THE
PREVIOUS FORECASTS AND JUST SOUTH OF THE GFDL AND A LITTLE NORTH OF
THE AVIATION/AVN MODEL.
 
SLOW AND STEADY INTENSIFICATION IS FORECAST THROUGH THE PERIOD.
HOWEVER...IF DEBBY SLOWS JUST A FEW KNOTS...THEN THE LOW-LEVEL
AND MID-LEVEL CIRCULATIONS WOULD BECOME VERTICALLY STACKED...MAKING
DEBBY MUCH STRONGER THAN THE OFFICIAL FORECAST IS INDICATING. THE
INITIAL WIND RADII WERE INCREASED BASED ON RECON AND 18Z WIND
REPORTS...WHILE THE 12 FT SEAS RADII WERE UNCHANGED.
 
FORECASTER STEWART
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL     21/2100Z 16.3N  59.4W    60 KTS
12HR VT     22/0600Z 16.7N  62.1W    70 KTS
24HR VT     22/1800Z 17.8N  65.7W    75 KTS
36HR VT     23/0600Z 18.8N  68.8W    70 KTS
48HR VT     23/1800Z 20.0N  71.5W    65 KTS
72HR VT     24/1800Z 22.5N  76.5W    85 KTS
 
 
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