000 WTNT43 KNHC 220245 TCDAT3 HURRICANE BILL DISCUSSION NUMBER 27 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL032009 1100 PM AST FRI AUG 21 2009 THE STRUCTURE OF BILL HAS CONTINUED TO EVOLVE THIS EVENING...WITH MICROWAVE IMAGERY SHOWING THE REMNANT OF AN INNER EYEWALL AND THE FORMATION OF AN OUTER EYEWALL. ALSO...THERE HAVE ALSO BEEN SIGNS OF A LARGER EYE TRYING TO FORM IN GEOSTATIONARY INFRARED IMAGERY IN THE PAST COUPLE OF HOURS. OVERALL...THE CLOUD PATTERN LOOKS LESS IMPRESSIVE...AS COLD CLOUD TOPS HAVE DIMINISHED OVER THE WESTERN SEMICIRCLE. ALL THAT BEING SAID...THE INITIAL INTENSITY IS HELD AT 90 KT BASED ON 0000 UTC DVORAK T-NUMBERS OF 5.0 FROM TAFB AND SAB...BUT THIS COULD BE GENEROUS. AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT IS CURRENTLY IN ROUTE TO INVESTIGATE BILL AND WILL PROVIDE MORE INFORMATION ON THE INTENSITY AND STRUCTURE OF THE CYCLONE IN THE NEXT FEW HOURS. IF BILL IS ABLE TO COMPLETE THE EYEWALL REPLACEMENT CYCLE...THERE IS SOME OPPORTUNITY FOR RESTRENGTHENING IN THE NEXT 24 HOURS BEFORE THE HURRICANE CROSSES THE NORTHERN WALL OF THE GULF STREAM...AND SOME STRENGTHENING IS SHOWN IN THE OFFICIAL FORECAST. THERE IS THE POSSIBILITY THAT BILL COULD INTENSIFY A LITTLE MORE THAN SHOWN HERE...AS THE INTENSITY PROBABILITY TABLE SHOWS ABOUT A 30 TO 35 PERCENT CHANCE THAT BILL WILL BE A CATEGORY 3 HURRICANE IN 12 TO 24 HOURS. BEYOND 24 HOURS...STEADY WEAKENING IS FORECAST AS THE CYCLONE ENCOUNTERS MUCH LOWER SEA SURFACE TEMPERATURES AND INCREASING WIND SHEAR. EXTRATROPICAL TRANSITION IS EXPECTED TO OCCUR IN TWO OR THREE DAYS...AND THE WIND RADII AND INTENSITY FORECASTS ATTEMPT TO ACCOUNT FOR THESE STRUCTURAL CHANGES. THE INITIAL MOTION ESTIMATE IS 345/17. THE TRACK GUIDANCE REMAINS IN VERY GOOD AGREEMENT...ACCELERATING BILL TOWARD THE NORTH AND NORTHEAST AHEAD OF A LARGE MID-LATITUDE TROUGH MOVING INTO THE NORTHEASTERN UNITED STATES. AS A RESULT...ONLY MINOR CHANGES HAVE BEEN MADE TO THE PREVIOUS PACKAGE. 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. WHILE TROPICAL-STORM-FORCE WINDS ARE NOT CURRENTLY FORECAST TO REACH NEW ENGLAND...A SHIFT IN THE FORECAST TRACK TO THE LEFT COULD REQUIRE THE ISSUANCE OF A TROPICAL STORM WATCH OR WARNING ON SATURDAY. THE WIND SPEED PROBABILITY PRODUCT INDICATES A 15 TO 20 PERCENT CHANCE OF TROPICAL-STORM-FORCE WINDS REACHING EXTREME SOUTHEASTERN NEW ENGLAND. THE INITIAL WIND RADII WERE ADJUSTED BASED ON DATA FROM A 2322 UTC QUIKSCAT PASS...DATA FROM NOAA BUOY 41048 AND OBSERVATIONS FROM BERMUDA. FORECAST POSITIONS AND MAX WINDS INITIAL 22/0300Z 31.0N 67.5W 90 KT 12HR VT 22/1200Z 33.5N 68.1W 95 KT 24HR VT 23/0000Z 37.3N 67.8W 95 KT 36HR VT 23/1200Z 41.3N 65.4W 80 KT 48HR VT 24/0000Z 45.1N 59.9W 70 KT 72HR VT 25/0000Z 50.5N 40.0W 45 KT...EXTRATROPICAL 96HR VT 26/0000Z 55.0N 19.0W 40 KT...EXTRATROPICAL 120HR VT 27/0000Z 60.5N 6.0W 35 KT...EXTRATROPICAL $$ FORECASTER BRENNAN