Tropical Storm DEBBY

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TROPICAL STORM DEBBY DISCUSSION NUMBER   6
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL042006
1100 PM EDT TUE AUG 22 2006
 
ALTHOUGH CONVECTIVE TOPS HAVE WARMED OVER THE PAST FEW HOURS...
ENOUGH CONVECTION HAS PERSISTED NEAR THE CENTER TO SUPPORT A
CONSENSUS SATELLITE INTENSITY ESTIMATE OF T2.5/35 KT FROM ALL THREE
AGENCIES. ALSO...THE PAST 5 AMSU INTENSITY ESTIMATES FROM UW-CIMSS
AND CIRA HAVE RANGED FROM 1003-1000 MB AND 38-43 KT. ALSO...A
22/2027Z QUIKSCAT OVERPASS SHOWED SEVERAL 30-35 KT UNCONTAMINATED
WIND VECTORS AROUND THE CIRCULATION CENTER. BASED ON THIS
INFORMATION...TD-4 HAS BEEN UPGRADED TO TROPICAL STORM DEBBY...THE
FOURTH NAMED STORM OF THE 2006 SEASON.

THE INITIAL MOTION ESTIMATE IS 295/16. ALTHOUGH THE GLOBAL MODELS
ARE IN REASONABLE AGREEMENT AND TIGHTLY CLUSTERED THROUGH 48-72H...
THE MODEL CONSENSUS HAS SHIFTED WELL TO THE WEST OR LEFT OF THE
PREVIOUS TRACK...DUE IN PART TO THE CONTINUED WESTWARD SHIFT OF
THE GFS...GFS ENSEMBLE...AND GFDL MODELS. THE BAM MODELS HAVE BEEN
ATROCIOUS AT BEST WITH A LARGE RIGHT-OF-TRACK BIAS OVER THE PAST 36
HOURS...SO THEY WERE NOT EVEN CONSIDERED IN THE FORECAST PROCESS.
THE GFS AND GFDL MODELS APPEAR TO HAVE BEEN OVERDEVELOPING A WEAK
MID- TO UPPER-LEVEL LOW LOCATED ABOUT 550 NMI NORTHWEST OF DEBBY.
THIS FEATURE IS SO INDISTINCT AND MUCH SMALLER THAN THE CIRCULATION
ENVELOPE OF DEBBY THAT IT IS HARD TO LOCATE IN WATER VAPOR IMAGERY.
IN CONTRAST...THE NOGAPS AND UKMET MODELS HAVE BEEN DOWNPLAYING THE
UPPER-LOW AND DISSIPATE IT COMPLETELY BY 48 HOURS. GIVEN THAT THE
UPPER-LOW AT BEST IS MOVING WESTWARD AT THE SAME SPEED AS DEBBY...
ANY NORTHWARD INFLUENCE BY THIS SYSTEM ON DEBBY SHOULD BE LESS THAN
DEPICTED BY THE GFS AND GFDL MODELS. THE OFFICIAL FORECAST TRACK
WAS SHIFTED WESTWARD...BUT NOT AS FAR WEST AS THE GUNA...GUNS...AND
CONU CONSENSUS MODELS. AS MENTIONED IN LAST NIGHT'S DISCUSSION...
IF DEBBY DOESN'T REACH 20-25N LATITUDE IN 72-96 HOURS...THEN A
SHORTWAVE TROUGH AND FORECAST WEAKNESS IN THE SUBTROPICAL RIDGE
WILL BYPASS THE CYCLONE...AS ALLUDED TO BY THE 18Z UKMET MODEL RUN.
 
DRIER MID-LEVEL AIR...COOLER SSTS...AND A SLIGHTLY MORE STABLE
AIRMASS AHEAD OF DEBBY SUGGEST THAT ANY STRENGTHENING SHOULD BE
SLOW THROUGHOUT THE FORECAST PERIOD. THE INTENSIFICATION TREND WAS
LEVELED OFF BETWEEN 24-48 HOURS AS DEBBY IS EXPECTED TO MOVE OVER
26C SSTS. AFTER THAT...THE CYCLONE IS FORECAST TO PASS OVER 28C AND
WARMER SSTS...BUT ONLY GRADUAL INTENSIFICATION IS EXPECTED DUE TO
SLOWLY INCREASING SOUTHERLY VERTICAL WIND SHEAR.

FORECAST POSITIONS AND MAX WINDS
 
INITIAL      23/0300Z 15.2N  28.9W    35 KT
 12HR VT     23/1200Z 16.2N  31.1W    40 KT
 24HR VT     24/0000Z 17.6N  33.8W    45 KT
 36HR VT     24/1200Z 18.9N  36.6W    45 KT
 48HR VT     25/0000Z 20.2N  39.5W    50 KT
 72HR VT     26/0000Z 22.8N  44.9W    55 KT
 96HR VT     27/0000Z 26.0N  50.0W    60 KT
120HR VT     28/0000Z 29.1N  54.0W    65 KT
 
$$
FORECASTER STEWART
 
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