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| #289640 (Received by flhurricane at: 10:49 AM 20.Aug.2009) TCDAT3 HURRICANE BILL DISCUSSION NUMBER 21 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL032009 1100 AM AST THU AUG 20 2009 CONVENTIONAL SATELLITE...MICROWAVE IMAGES AND NUMEROUS OBSERVATIONS FROM A NOAA P-3 RESEARCH PLANE INDICATE THAT BILL HAS WEAKENED A LITTLE BIT DURING THE PAST SEVERAL HOURS. DVORAK T-NUMBERS HAVE DECREASED SINCE YESTERDAY...THE EYEWALL HAS BECOME OPEN TO THE SOUTHWEST AND THE MAXIMUM FLIGHT LEVEL AND SFMR WINDS WERE 121 AND 93 KNOTS...RESPECTIVELY...EARLIER THIS MORNING. IN FACT...SOME ARC CLOUDS ARE MOVING AWAY FROM THE HURRICANE SUGGESTING THAT BILL IS NOT STRENGTHENING AT THIS TIME. BASED ON THESE DATA...THE INITIAL INTENSITY HAS BEEN REDUCED TO 105 KNOTS...AND THIS IS PROBABLY ON THE HIGH SIDE. THE LARGE SCALE ENVIRONMENT IS CONDUCIVE FOR REINTENSIFICATION SINCE BILL IS ABOUT TO ENCOUNTER THE WARMEST WATERS ALONG ITS PATH SO FAR...AND THE SHEAR IS FORECAST TO BE QUITE LIGHT. HOWEVER...MOST OF THE INTENSITY CHANGE COULD BE ASSOCIATED WITH EYEWALL REPLACEMENT CYCLES. THE OFFICIAL FORECAST CALLS FOR RESTRENGTHENING AND BILL IS EXPECTED TO REACH CATEGORY FOUR AGAIN IN A DAY OR SO. THEREAFTER...THE HURRICANE SHOULD GRADUALLY BEGIN TO INTERACT WITH A MID-LATITUDE TROUGH AND BY 96 HOURS IT SHOULD BE IN EXTRATROPICAL TRANSITION AND BE FULLY EXTRATROPICAL IN FIVE DAYS. BILL HAS CONTINUED TO MOVE ON A STEADY NORTHWEST TRACK OR 305 DEGREES AT 16 KNOTS...EMBEDDED WITHIN THE FLOW SURROUNDING THE AZORES-BERMUDA HIGH. IN ABOUT TWO DAYS...THE HURRICANE WILL BECOME STEERED NORTHWARD AND THEN NORTHEASTWARD BY THE FLOW BETWEEN A LARGE MID-LATITUDE TROUGH SWINGING EASTWARD ACROSS THE EASTERN UNITED STATES AND THE SUBTROPICAL HIGH. ONCE THE RECURVATURE BEGINS...THE HURRICANE SHOULD INCREASE IN FORWARD SPEED. MOST OF THE TRACK GUIDANCE SHIFTED SLIGHTLY TO THE WEST COMPARED TO THE PREVIOUS RUN. THIS SHIFT IN GUIDANCE JUSTIFIES A VERY SMALL SHIFT TO THE WEST OF THE TRACK OFFICIAL FORECAST...WHICH INDEED IS VERY CLOSE TO THE CONSENSUS. LARGE SWELLS GENERATED BY THIS HURRICANE ARE AFFECTING THE NORTHERN LEEWARD ISLANDS AND SHOULD BEGIN AFFECTING THE BAHAMAS...BERMUDA... MOST OF THE EASTERN U.S. COAST...AND THE ATLANTIC MARITIMES OF CANADA DURING THE NEXT FEW DAYS. THESE SWELLS WILL LIKELY CAUSE EXTREMELY DANGEROUS SURF AND LIFE-THREATENING RIP CURRENTS. PLEASE CONSULT STATEMENTS ISSUED BY YOUR LOCAL WEATHER OFFICE FOR MORE DETAILS. THIS AFTERNOON NOAA AND THE 53RD HURRICANE HUNTERS WILL BE CONDUCTING A TWO-AIRCRAFT SYNOPTIC SURVEILLANCE MISSION AROUND HURRICANE BILL TO IMPROVE THE INITIAL ANALYSIS FOR THE NUMERICAL MODELS. FORECAST POSITIONS AND MAX WINDS INITIAL 20/1500Z 22.6N 61.7W 105 KT 12HR VT 21/0000Z 24.2N 63.8W 110 KT 24HR VT 21/1200Z 26.6N 66.0W 115 KT 36HR VT 22/0000Z 29.5N 67.5W 115 KT 48HR VT 22/1200Z 32.5N 69.0W 110 KT 72HR VT 23/1200Z 40.5N 66.5W 100 KT 96HR VT 24/1200Z 48.0N 53.0W 65 KT...BECOMING EXTRATROPICAL 120HR VT 25/1200Z 55.0N 28.0W 50 KT...EXTRATROPICAL $$ FORECASTER AVILA |
