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HURRICANE DEBBY DISCUSSION NUMBER  11
NATIONAL WEATHER SERVICE MIAMI FL
5 AM EDT TUE AUG 22 2000
 
DEBBY HAS STRENGTHENED INTO A 65 KT HURRICANE DURING THE NIGHT BASED
ON DROPSONDE MEASUREMENTS OF HURRICANE FORCE SURFACE WINDS.  AN
EARLIER SHARP DROP IN CENTRAL PRESSURE WAS LIKELY CAUSED BY A
SUPERCELL-TYPE THUNDERSTORM DEVELOPING NEAR THE CENTER.  THIS
TIGHTLY-WOUND FEATURE QUICKLY DISSIPATED AND THE CENTRAL PRESSURE
ROSE FROM 991 MB TO 994 MB.  SINCE THEN...THE GUADELOUPE RADAR HAS
SHOWN THE FORMATION OF A MORE CLASSIC BANDING PATTERN.

AIRCRAFT AND RADAR DATA SUGGEST A SLIGHT TURN TO THE RIGHT AND THE
INITIAL MOTION IS NOW 290/18.  THE REASON FOR THIS MIGHT BE THE
SOUTHERLY UPPER LEVEL FLOW BLOWING ACROSS THE NOW DEEPER VORTEX.
THERE IS NO CHANGE IN THE SYNOPTIC REASONING...AS LOW/MID LEVEL
RIDGING SHOULD KEEP DEBBY ON A GENERAL WEST-NORTHWESTERLY TRACK
THROUGH THE FORECAST PERIOD.  DESPITE THIS...SOME DIFFERENCES HAVE
DEVELOPED IN THE MODELS.  THE NOGAPS AND AVN TAKE DEBBY ON A MORE
WESTERLY COURSE OVER HISPANIOLA AND CUBA INTO THE GULF OF MEXICO.
THEY ARE SUPPORTED BY THE BAMS AND THE NHC90.  THE UKMET CALLS FOR A
MORE NORTHERLY MOTION...TAKING DEBBY THROUGH THE CENTRAL AND EASTERN
BAHAMAS.  IT IS SUPPORTED BY LBAR AND VICBAR.  THE GFDL AND GFDN ARE
DOWN THE MIDDLE OF THE GUIDANCE SUITE...AND THE OFFICIAL FORECAST
AGREES BEST WITH THE GFDN.  THERE IS A POSSIBILITY OF A STAIR-STEP
TRACK...A MORE NORTHWARD MOTION NOW FOLLOWED BY A MORE WESTWARD
MOTION LATER.  THIS IS SUPPORTED BY WATER VAPOR IMAGERY...WHICH
INDICATES A SHORTWAVE TROUGH BETWEEN THE SOUTHEASTERN U.S. AND
BERMUDA...AND LARGE-SCALE MODEL FORECAST OF HEIGHT RISES OVER THE
WESTERN ATLANTIC AFTER 24-36 HR.

THE CONTINUED RAPID MOTION IS KEEPING ABOUT 10 KT OF SHEAR OVER
DEBBY...WHICH IS SLOWING INTENSIFICATION.  THIS IS LIKELY TO
CONTINUE FOR THE NEXT 24-36 HR...SO EARLY IN THE PERIOD FURTHER
STRENGTHENING IS LIKELY TO BE SLOW AND UNSTEADY.  AS THE STORM
SLOWS...CONDITIONS MAY BE MORE FAVORABLE FOR DEVELOPMENT IF DEBBY IS
NOT OVER HISPANIOLA OR IS NOT UNDER THE 200 MB NORTHWEST FLOW
FORECAST OVER PORTIONS OF THE WESTERN ATLANTIC BY 72 HR.  IF THESE
EXTREMES DO NOT OCCUR...DEBBY MAY BE STRONGER THAN CURRENTLY
FORECAST BY 72 HR.
 
FORECASTER BEVEN
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL     22/0900Z 17.7N  62.6W    65 KTS
12HR VT     22/1800Z 18.5N  65.3W    70 KTS
24HR VT     23/0600Z 19.4N  68.7W    75 KTS
36HR VT     23/1800Z 20.4N  71.9W    75 KTS
48HR VT     24/0600Z 21.5N  74.5W    80 KTS
72HR VT     25/0600Z 23.5N  78.5W    85 KTS
 
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