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| #290297 (Received by flhurricane at: 5:05 AM 22.Aug.2009) TCDAT3 HURRICANE BILL DISCUSSION NUMBER 28 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL032009 500 AM AST SAT AUG 22 2009 REPORTS FROM AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT INDICATE THAT BILL HAS JUST ABOUT FINISHED ITS EYEWALL REPLACEMENT CYCLE... AND NOW HAS A 48 N MI WIDE EYE. THE AIRCRAFT ENCOUNTERED 120 KT FLIGHT-LEVEL WINDS AT 700 MB IN THE NORTHEASTERN EYEWALL...AND A DROPSONDE IN THE AREA SUGGESTS SURFACE WINDS OF 90 KT. THE MINIMUM CENTRAL PRESSURE WAS 960 MB. BASED ON THIS DATA...THE INITIAL INTENSITY REMAINS 90 KT. THE CIRRUS OUTFLOW IS GOOD IN THE NORTHWESTERN SEMICIRCLE AND POOR ELSEWHERE. BILL HAS MOVED A LITTLE TO THE LEFT OF THE PREVIOUS FORECAST...WITH AN INITIAL MOTION OF 345/19. OTHER THAN THAT...THERE IS LITTLE CHANGE IN THE FORECAST PHILOSOPHY OR THE TRACK FORECAST GUIDANCE. BILL IS EXPECTED TO RECURVE INTO THE WESTERLIES DURING THE NEXT 24-48 HR BETWEEN A LARGE DEEP-LAYER TROUGH OVER THE EASTERN UNITED STATES AND A RIDGE OVER THE CENTRAL ATLANTIC. AFTER 48 HR...THE SYSTEM SHOULD MOVE QUICKLY EASTWARD IN THE WESTERLIES. THE NEW FORECAST TRACK IS SLIGHTLY NORTH AND WEST OF THE PREVIOUS TRACK FOR THE FIRST 48 HR DUE TO THE INITIAL POSITION AND MOTION. AFTER THAT TIME...THE TRACK IS SHIFTED SOUTHWARD FROM THE PREVIOUS TRACK. THE NEW FORECAST IS DOWN THE MIDDLE OF THE DYNAMICAL GUIDANCE ENVELOPE. BILL SHOULD REMAIN IN LIGHT VERTICAL WIND SHEAR AND OVER WARM SEA SURFACE TEMPERATURES FOR THE NEXT 12-24 HOURS...AND THUS THE INTENSITY FORECAST CALLS FOR SOME STRENGTHENING DURING THIS TIME. AFTER 24 HR...COLDER SSTS AND INCREASING SHEAR SHOULD CAUSE BILL TO WEAKEN. EXTRATROPICAL TRANSITION IS EXPECTED TO BEGIN AT ABOUT THE 48 HR PERIOD AND BE COMPLETE BY 72 HR...AND THE EXTRATROPICAL REMNANTS OF BILL ARE FORECAST TO GRADUALLY WEAKEN AS THEY CROSS THE ATLANTIC. LARGE SWELLS GENERATED BY BILL ARE BEGINNING TO ARRIVE ALONG THE EAST COAST OF THE UNITED STATES. THESE SWELLS WILL SPREAD NORTHWARD OVER THE WEEKEND...CAUSING EXTREMELY DANGEROUS SURF AND LIFE-THREATENING RIP CURRENTS. PLEASE CONSULT STATEMENTS ISSUED BY YOUR LOCAL WEATHER OFFICE AND METEOROLOGICAL SERVICES FOR MORE DETAILS. THE WESTWARD SHIFT IN THE FORECAST TRACK REQUIRES A TROPICAL STORM WARNING FOR PORTIONS OF THE MASSACHUSETTS COAST...AND THE WIND SPEED PROBABILITY PRODUCT NOW SHOWS A 40 PERCENT CHANCE OF TROPICAL-STORM-FORCE WINDS IN THAT AREA. ANY ADDITIONAL TRACK DEVIATIONS TO THE WEST WOULD REQUIRE ADDITIONAL WARNINGS ALONG THE NEW ENGLAND COAST. FORECAST POSITIONS AND MAX WINDS INITIAL 22/0900Z 33.0N 68.5W 90 KT 12HR VT 22/1800Z 36.1N 68.7W 95 KT 24HR VT 23/0600Z 40.1N 67.2W 90 KT 36HR VT 23/1800Z 44.1N 63.1W 75 KT 48HR VT 24/0600Z 48.0N 55.6W 60 KT...INLAND 72HR VT 25/0600Z 51.0N 31.5W 40 KT...EXTRATROPICAL 96HR VT 26/0600Z 54.0N 14.0W 30 KT...EXTRATROPICAL 120HR VT 27/0600Z 58.0N 4.0W 20 KT...EXTRATROPICAL $$ FORECASTER BEVEN |
