000 WTNT43 KNHC 240234 TCDAT3 HURRICANE BILL DISCUSSION NUMBER 35 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL032009 1100 PM AST SUN AUG 23 2009 BILL STILL HAS STRUCTURAL CHARACTERISTICS OF A TROPICAL CYCLONE... WITH DEEP CONVECTION NEAR THE CENTER AND A FRAGMENT OF AN EYEWALL VISIBLE IN MICROWAVE IMAGERY FROM A 2304 UTC SSMIS PASS. BASED ON THE INNER-CORE STRUCTURE...AND A DVORAK CI NUMBER OF 4.0 FROM TAFB AT 0000 UTC...BILL IS MAINTAINED AS A 65 KT HURRICANE FOR THIS ADVISORY. BILL HAS ACCELERATED TOWARD THE EAST-NORTHEAST OVER THE PAST SEVERAL HOURS...AND THE INITIAL MOTION ESTIMATE IS 060/35. BILL IS EXPECTED TO REMAIN ON AN EAST-NORTHEASTWARD HEADING UNDER THE INFLUENCE OF THE MID-LATITUDE WESTERLIES FOR THE NEXT COUPLE OF DAYS...AND THE TRACK GUIDANCE REMAINS IN EXCELLENT AGREEMENT ON THIS SCENARIO. AFTER 48 HOURS...BILL WILL SLOW DOWN AND TURN TOWARD THE NORTH AS IT COMES UNDER THE INFLUENCE OF A MUCH LARGER EXTRATROPICAL CYCLONE LOCATED SOUTHWEST OF ICELAND. BILL WILL EVENTUALLY BE ABSORBED INTO THIS LARGER CIRCULATION BY 96 HOURS. THE NEW OFFICIAL FORECAST IS A LITTLE FASTER THAN THE PREVIOUS PACKAGE...AND IS CLOSE TO THE MULTI-MODEL CONSENSUS. BILL IS BEGINNING TO UNDERGO EXTRATROPICAL TRANSITION...WITH THE UPPER-LEVEL CLOUD PATTERN EXPANDING NORTH AND EAST OF THE CENTER IN THE ENTRANCE REGION OF A 140-KT UPPER-LEVEL JET CORE CENTERED ALONG 55N. ALSO...DATA FROM A 2226 UTC QUIKSCAT PASS ALONG WITH NUMEROUS SURFACE OBSERVATIONS SHOW THAT THE WIND FIELD OF BILL HAS BEGUN TO EXPAND...PARTICULARLY IN THE SOUTHEASTERN QUADRANT. MOST OF THE GLOBAL MODEL GUIDANCE INDICATES THAT BILL WILL COMPLETE THE EXTRATROPICAL TRANSITION PROCESS WITHIN 12 TO 24 HOURS. AFTER THAT TIME...UPPER-LEVEL DIVERGENCE ASSOCIATED WITH THE JET WILL HELP MAINTAIN BILL AS AN EXTRATROPICAL CYCLONE...AND THE OFFICIAL INTENSITY FORECAST SHOWS GRADUAL WEAKENING AS BILL MOVES ACROSS THE NORTHERN ATLANTIC. AS BILL BECOMES FULLY EXTRATROPICAL...THE WIND FIELD WILL CONTINUE TO EXPAND...ESPECIALLY IN THE SOUTHERN SEMICIRCLE. LARGE AND DANGEROUS SWELLS ASSOCIATED WITH BILL WILL CONTINUE IMPACTING THE CANADIAN MARITIMES DURING THE NEXT 12 TO 24 HOURS... WHILE SWELLS ALONG THE EAST COAST OF THE UNITED STATES WILL CONTINUE TO SUBSIDE OVERNIGHT. FORECAST POSITIONS AND MAX WINDS INITIAL 24/0300Z 47.1N 55.5W 65 KT 12HR VT 24/1200Z 49.1N 47.9W 55 KT 24HR VT 25/0000Z 50.8N 36.0W 45 KT...EXTRATROPICAL 36HR VT 25/1200Z 52.2N 24.5W 40 KT...EXTRATROPICAL 48HR VT 26/0000Z 53.5N 14.7W 35 KT...EXTRATROPICAL 72HR VT 27/0000Z 61.0N 2.0W 30 KT...EXTRATROPICAL 96HR VT 28/0000Z...DISSIPATED $$ FORECASTER BRENNAN