Tropical Storm DEBBY

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TROPICAL STORM DEBBY DISCUSSION NUMBER  10
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL042006
1100 PM EDT WED AUG 23 2006
 
AFTER THE BRIEF WEAKENING PHASE DEBBY WENT THROUGH EARLIER AS
MENTIONED IN THE PREVIOUS DISCUSSION...THE CYCLONE HAS STARTED TO
MAKE A COMEBACK. DEEP CONVECTION HAS REDEVELOPED IN THE WESTERN
SEMICIRCLE...AND MICROWAVE SATELLITE DATA INDICATE GOOD BANDING
FEATURES AND THAT THE LOW-LEVEL CENTER IS UNDERNEATH THE NORTHEAST
PORTION OF THE CONVECTIVE CLOUD CANOPY. THE INTENSITY IS BEING
MAINTAINED AT 40 KT AS IN THE PREVIOUS ADVISORY DESPITE SATELLITE
INTENSITY ESTIMATES OF ONLY 30 KT FROM ALL THREE AGENCIES.
 
THE INITIAL MOTION ESTIMATE IS 300/16. CONVENTIONAL AND MICROWAVE
SATELLITE POSITION ESTIMATES INDICATE DEBBY IS BASICALLY ON TRACK.
A GRADUAL MOTION CLOSE TO 290 DEGREES IS EXPECTED TO OCCUR WITHIN
THE NEXT 24 HOURS DUE TO MID- TO UPPER-LEVEL SOUTHEASTERLY FLOW
FORCING THE CYCLONE ON A SLIGHTLY MORE WESTWARD TRACK NOW THAT DEEP
CONVECTION HAS REDEVELOPED ON THE WEST SIDE OF DEBBY. OTHERWISE
DEBBY IS FORECAST FOR THE NEXT 4 DAYS TO TO BE STEERED
WEST-NORTHWESTWARD AND THEN NORTHWESTWARD AROUND THE SOUTHWESTERN
PERIPHERY OF A DEEP-LAYER SUBTROPICAL RIDGE LOCATED TO THE NORTH.
BY THE DAY 4-5 TIME PERIOD...ALL THE MODELS AGREE THAT A WEAKNESS
WILL DEVELOP IN THE SUBTROPICAL RIDGE BETWEEN 50W-55W LONGITUDE...
ALLOWING DEBBY TO MOVE NORTHWARD INTO THAT WEAKNESS. THE UKMET AND
GFDL MODELS INDICATE RECURVATURE TO THE NORTHEAST BY DAY 5...
WHEREAS THE REST OF THE MODELS MERELY SLOW DOWN THE CYCLONE AND
MOVE IT NORTHWARD INTO THE WEAKNESS. THE GFS IS NOW SUGGESTING THAT
THE SHORTWAVE TROUGH EXPECTED TO CAUSE THE BREAK IN THE SUBTROPICAL
RIDGE MAY RUN OFF AND LEAVE DEBBY CAUGHT IN THE RIDGE AXIS. THE
OFFICIAL FORECAST TRACK IS SIMILAR TO THE PREVIOUS TRACK AND THE
GUNA...GUNS...AND CONU CONSENSUS MODELS.
 
DEBBY IS CURRENTLY OVER 26C SSTS...THE COOLEST WATER IT WILL
ENCOUNTER DURING THE NEXT 5 DAYS. VERTICAL SHEAR IS FORECAST TO
DECREASE TO LESS THAN 10 KT DURING THE NEXT 12-24 HOURS...SO SOME
GRADUAL STRENGTHENING IS POSSIBLE AS THE CYCLONE MOVES OVER WARMER
SSTS. BY 72 HOURS... THE VERTICAL SHEAR IS EXPECTED TO INCREASE TO
AT LEAST 20 KT...WHICH WILL INHIBIT INTENSIFICATION DESPITE DEBBY
MOVING OVER 28C AND WARMER SSTS. HOWEVER...GIVEN THAT THE VERTICAL
SHEAR VECTOR WILL BE ALIGNED NEARLY ALONG THE FORECAST TRACK...
DEBBY COULD STILL BECOME A CATEGORY 1 HURRICANE...ESPECIALLY BY DAY
5 WHEN THE CYCLONE WILL BE SITUATED IN THE WEAKNESS IN THE
SUBTROPICAL RIDGE AND...THUS...IN A LOWER SHEAR ENVIRONMENT.

FORECAST POSITIONS AND MAX WINDS
 
INITIAL      24/0300Z 18.8N  34.7W    40 KT
 12HR VT     24/1200Z 19.8N  36.8W    40 KT
 24HR VT     25/0000Z 21.1N  39.7W    45 KT
 36HR VT     25/1200Z 22.3N  42.5W    50 KT
 48HR VT     26/0000Z 23.6N  45.0W    55 KT
 72HR VT     27/0000Z 26.4N  49.2W    60 KT
 96HR VT     28/0000Z 29.5N  51.5W    65 KT
120HR VT     29/0000Z 33.0N  51.5W    65 KT
 
$$
FORECASTER STEWART
 
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