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| #105594 (Received by flhurricane at: 11:05 PM 22.Aug.2006) TCDAT4 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 |
