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| #289342 (Received by flhurricane at: 10:43 PM 18.Aug.2009) TCDAT3 HURRICANE BILL DISCUSSION NUMBER 15 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL032009 1100 PM AST TUE AUG 18 2009 REPORTS FROM A NOAA HURRICANE HUNTER AIRCRAFT CONDUCTING A RESEARCH MISSION IN BILL AND INFRARED SATELLITE IMAGERY INDICATE THAT BILL HAS UNDERGONE A PERIOD OF RAPID INTENSIFICATION AND IS NOW A MAJOR HURRICANE. HIGHEST FLIGHT-LEVEL WINDS SO FAR HAVE BEEN 126 KT AT 700 MB...WITH THE LATEST MINIMUM PRESSURE OF 952 MB AT 0202 UTC. THE HIGHEST SFMR-OBSERVED SURFACE WIND SPEED WAS 100 KT. THE LATEST DVORAK T-NUMBERS ARE 6.0 FROM BOTH TAFB AND SAB...WHILE UW CIMSS OBJECTIVE ADVANCED DVORAK VALUES HAVE BEEN AS HIGH AS 7.0. BLENDING THE AIRCRAFT FLIGHT-LEVEL...SFMR...AND DROPSONDE WINDS WITH THE VARIOUS SATELLITE-DERIVED INTENSITY ESTIMATES...THE INITIAL INTENSITY IS SET AT 110 KT. FAVORABLE ENVIRONMENTAL CONDITIONS COULD ALLOW FOR FURTHER STRENGTHENING DURING THE NEXT 24 TO 36 HOURS. HOWEVER...EYEWALL REPLACEMENT CYCLES...WHICH ARE VERY DIFFICULT TO ANTICIPATE...MAY PRODUCE SOME FLUCTUATIONS IN INTENSITY. REGARDLESS...BILL IS EXPECTED TO REMAIN A LARGE AND POWERFUL HURRICANE FOR SEVERAL DAYS AS IT MARCHES INTO THE CENTRAL NORTH ATLANTIC. TOWARD THE END OF THE PERIOD...SEA SURFACE TEMPERATURES WILL BE DECREASING ALONG THE FORECAST TRACK AND SOUTHERLY TO SOUTHWESTERLY SHEAR SHOULD BEGIN TAKING A TOLL. AS A RESULT...THE OFFICIAL INTENSITY FORECAST CALLS FOR WEAKENING AROUND 96 HOURS...WITH A MORE DECIDED RATE OF WEAKENING NEAR THE END OF THE PERIOD. BASED ON AIRCRAFT AND SATELLITE FIXES...THE INITIAL MOTION IS ESTIMATED TO BE 295/13...REPRESENTING A SLIGHTLY MORE NORTHERLY COMPONENT OF MOTION. THE TRACK FORECAST PHILOSOPHY HAS NOT CHANGED. BILL IS FORECAST TO BE STEERED NORTHWESTWARD INTO A SIGNIFICANT BREAK IN THE SUBTROPICAL RIDGE OVER THE NEXT FEW DAYS...WHERE IT WILL COME UNDER THE INFLUENCE OF AN UNUSUALLY DEEP LONGWAVE TROUGH DIGGING INTO THE EASTERN UNITED STATES. THIS STEERING FEATURE SHOULD CAUSE BILL TO TURN NORTHWARD AND THEN NORTH-NORTHEASTWARD...WITH SOME INCREASE IN FORWARD SPEED. THE TRACK GUIDANCE IS IN REASONABLY GOOD AGREEMENT ON THIS SCENARIO...WITH THE OFFICIAL TRACK IN THE MIDDLE OF GUIDANCE ENVELOPE. FORECAST POSITIONS AND MAX WINDS INITIAL 19/0300Z 17.2N 53.4W 110 KT 12HR VT 19/1200Z 18.4N 55.4W 120 KT 24HR VT 20/0000Z 20.0N 58.0W 125 KT 36HR VT 20/1200Z 21.8N 60.5W 125 KT 48HR VT 21/0000Z 23.8N 62.9W 120 KT 72HR VT 22/0000Z 29.0N 67.0W 115 KT 96HR VT 23/0000Z 35.0N 68.0W 100 KT 120HR VT 24/0000Z 42.0N 64.0W 85 KT $$ FORECASTER KIMBERLAIN/PASCH |
