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| #46642 (Received by flhurricane at: 11:14 PM 17.Sep.2005) TCDAT3 TROPICAL DEPRESSION EIGHTEEN DISCUSSION NUMBER 1 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 11 PM EDT SAT SEP 17 2005 SATELLITE IMAGERY AND NEARBY BUOY AND SHIP OBSERVATIONS INDICATE THE TROPICAL DISTURBANCE LOCATED EAST OF THE TURKS AND CAICOS HAS ACQUIRED ENOUGH CONVECTIVE ORGANIZATION TO BE CLASSIFIED AS A TROPICAL DEPRESSION. THE INITIAL INTENSITY OF 25 KT IS BASED ON A SATELLITE INTENSITY ESTIMATE OF 25 KT FROM TAFB AND EARLIER SHIP REPORTS. BANDING HAS INCREASED IN THE EASTERN SEMICIRCLE AND SEVERAL MODERATE CONVECTIVE CELLS HAVE RECENTLY DEVELOPED AROUND THE SURFACE CENTER. THE INITIAL MOTION ESTIMATE IS 290/09. TD-18 IS EXPECTED TO MOVE WEST-NORTHWESTWARD FOR THE NEXT 48 HOURS TOWARD A WEAKNESS IN THE SUBTROPICAL RIDGE THAT LIES JUST EAST OF FLORIDA. AFTER THAT... MOST OF THE GLOBAL MODELS AGREE THAT THE WEAKNESS WILL GRADUALLY FILL AS THE RIDGE OVER TEXAS AND THE GULF COAST BUILDS EASTWARD. HOWEVER...THE EXACT TIMING OF THE FILLING RDIGE WEAKNESS IS UNCERTAIN AND THAT WILL DETERMINE HOW FAR NORTH THE CYCLONE MOVES BEFORE IT TURNS WESTWARD. THE GLOBAL MODELS AND THE GFDL MODEL KEEP THE SYSTEM OVER OR SOUTH OF THE FLORIDA KEYS. ONLY THE CANADIAN MODEL AND THE TIGHTLY PACKED BAM MODELS BRING THE STORM ACROSS THE SOUTHERN PORTION OF THE FLORIDA PENINSULA IN 60-72 HOURS. SINCE THE DEPRESSION IS STILL IN THE FORMATIVE STAGE...THE CIRCULATION CENTER COULD EASILY DEVELOP ANY WHERE WITHIN THE CONVECTIVE CLOUD MASS... WHICH COULD RESULT IN NORTH-SOUTH SHIFTS IN THE FORECAST TRACK DURING THE NEXT DAY OR SO. ALL INTERESTS IN THE BAHAMAS...SOUTH FLORIDA...THE FLORIDA KEYS...AND CENTRAL AND WESTERN CUBA SHOULD PAY CLOSE ATTENTION TO THIS SYSTEM OVER THE NEXT FEW DAYS. THE INTENSITY FORECAST IS MUCH MORE OF A CHALLENGE THAN THE TRACK FORECAST IS. THE VERTICAL SHEAR IS FORECAST TO DECREASE TO LESS THAN 10 KT IN THE 36-60 HOUR TIME FRAME...WHILE THE CYCLONE IS OVER 30C AND WARMER SSTS. THIS WOULD FAVOR RAPID INTENSIFICATION IF DRY MID-LEVEL AIR DOES NOT GET ENTRAINED INTO THE CENTER. AFTERWARDS... THE GFS-BASED SHIPS INTENSITY MODEL GRADUALLY INCREASES THE WESTERLY SHEAR TO MORE THAN 20 KT AND LEVELS OFF THE INTENSITY AT 73 KT. HOWEVER...THE NOGAPS...UKMET...AND CANADIAN MODELS SHOW A 200 MB ANTICYCLONE WITH AN EAST-WEST ORIENTED RIDGE AXIS EXTENDING ACROSS THE FLORIDA KEYS BY 48 HOURS. EVEN THE GFS DEVELOPS A SIMILAR UPPER-LEVEL PATTERN...ONLY ACROSS THE SOUTHERN FLORIDA PENINSULA. THE CLOSE PROXIMITY TO SUCH A FAVORABLE UPPER-LEVEL OUTFLOW PATTERN SUGGESTS THAT THIS TROPICAL CYCLONE COULD BE MUCH STRONGER BY 72 HOURS THAN WHAT IS CURRENTLY FORECAST BY THE SHIPS MODEL. THE 18Z GFDL MODEL RAPIDLY INTENSIFIES THE SYSTEM INTO A 120-KT HURRICANE IN 72 HOURS. WHILE THAT RATE OF INTENSIFICATION MAY BE A LITTLE EXCESSIVE...THIS SYSTEM REACHING STRONG CATEGORY 2 STATUS WITHIN THE NEXT 72 HOURS IS CERTAINLY A VIABLE SCENARIO. FORECASTER STEWART FORECAST POSITIONS AND MAX WINDS INITIAL 18/0300Z 22.0N 69.7W 25 KT 12HR VT 18/1200Z 22.5N 71.5W 35 KT 24HR VT 19/0000Z 23.1N 73.6W 40 KT 36HR VT 19/1200Z 23.6N 75.5W 50 KT 48HR VT 20/0000Z 24.0N 77.7W 60 KT 72HR VT 21/0000Z 24.5N 82.0W 70 KT 96HR VT 22/0000Z 25.0N 86.0W 75 KT 120HR VT 23/0000Z 25.0N 90.5W 80 KT |
