000 WTNT43 KNHC 192031 TCDAT3 HURRICANE BILL DISCUSSION NUMBER 18 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL032009 500 PM AST WED AUG 19 2009 VISIBLE SATELLITE IMAGES SHOW THAT BILL IS AN IMPRESSIVE HURRICANE WITH MESOCYCLONES NOTED IN THE EYE...CURVED BANDING FEATURES IN ALL QUADRANTS AND A WELL-ESTABLISHED OUTFLOW PATTERN. AN FORCE RESERVE HURRICANE HUNTER RECENTLY MEASURED 135 KT AT 700 MB...ALONG WITH SFMR WINDS OF 103 KT AND A MINIMUM PRESSURE OF 947 MB. IN ADDITION...THERE WAS AN SFMR MEASUREMENT OF 106 KT FROM THE NOAA MISSION THIS MORNING. SATELLITE CLASSIFICATION ARE 127 KT FROM TAFB/SAB AND THE INITIAL INTENSITY IS KEPT AT 115 KT AS A COMPROMISE OF ALL THESE DATA. VERY WARM WATERS ARE ALONG THE PATH OF THE HURRICANE FOR THE NEXT FEW DAYS. THE BIGGEST QUESTION IS WHETHER THE UPPER ENVIRONMENT WILL REMAIN FAVORABLE FOR STRENGTHENING. A PAIR OF UPPER-LEVEL TROUGHS HAVE THE POTENTIAL TO INDUCE SOME SHEAR ON BILL...ONE ALONG 60W AND OTHER AT ABOUT 70W. WHILE THE MODELS DISAGREE ON WHETHER THE FIRST TROUGH WILL AFFECT THE HURRICANE MUCH...MOST MODELS SHOW SOUTHWESTERLY SHEAR INCREASING IN A COUPLE DAYS AS A RESULT OF THE SECOND FEATURE. IN ADDITION...AN EYEWALL REPLACEMENT CYCLE COULD OCCUR AT ANY TIME WITH A SECONDARY WIND MAXIMUM NOTED AT ABOUT 75 N MI FROM THE CENTER IN AIRCRAFT DATA. REGARDLESS...ALL OF THE RELIABLE MODELS KEEP THE HURRICANE QUITE STRONG FOR THE NEXT SEVERAL DAYS...AND THE OFFICIAL INTENSITY FORECAST REFLECTS THAT LIKELIHOOD. THE ESTIMATED MOTION IS A LITTLE MORE TO THE RIGHT AND FASTER...NOW 305/17. STRONG SUBTROPICAL RIDGING SHOULD KEEP BILL ON THIS GENERAL TRACK FOR THE NEXT COUPLE OF DAYS WITH A GRADUAL BEND TOWARD THE NORTH-NORTHWEST BY THE WEEKEND AS THE HURRICANE MOVES INTO A BREAK IN THE RIDGE. SOME OF THE MODELS...SUCH AS THE GFS...NOW SHOW A SLIGHTLY STRONGER RIDGE OVER THE WESTERN ATLANTIC AND A SLOWER MID-LATITUDE TROUGH MOVING ACROSS THE EASTERN UNITED STATES. IF THIS SOLUTION IS CORRECT...BILL WOULD BE ABLE TO MOVE A LITTLE FARTHER TO THE WEST BEFORE TURNING TO THE NORTH AND NORTHEAST. THERE HAS BEEN A SMALL WESTWARD SHIFT IN MOST OF THE AFTERNOON MODEL GUIDANCE...AND THE OFFICIAL FORECAST IS SHIFTED IN THAT DIRECTION. THIS IS A GOOD TIME TO POINT OUT THAT THERE IS A LOT OF UNCERTAINTY IN THE LONG-RANGE TROPICAL CYCLONE FORECAST AND ONE SHOULD NOT FOCUS ON THE EXACT TRACK AT THOSE TIME PERIODS. BECAUSE BILL IS A LARGE AND STRONG HURRICANE...SWELLS TRIGGERED BY THE HURRICANE SHOULD AFFECT THE NORTHERN LEEWARD ISLANDS...THE BAHAMAS...BERMUDA AND MOST OF THE EASTERN UNITED STATES 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. FORECAST POSITIONS AND MAX WINDS INITIAL 19/2100Z 19.8N 57.6W 115 KT 12HR VT 20/0600Z 21.1N 59.7W 120 KT 24HR VT 20/1800Z 23.0N 62.4W 125 KT 36HR VT 21/0600Z 25.2N 64.6W 120 KT 48HR VT 21/1800Z 27.9N 66.6W 120 KT 72HR VT 22/1800Z 34.0N 69.0W 110 KT 96HR VT 23/1800Z 42.0N 65.5W 95 KT 120HR VT 24/1800Z 51.5N 50.5W 55 KT...EXTRATROPICAL $$ FORECASTER BLAKE