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| #289154 (Received by flhurricane at: 4:40 AM 18.Aug.2009) TCDAT3 HURRICANE BILL DISCUSSION NUMBER 12 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL032009 500 AM AST TUE AUG 18 2009 TRMM DATA FROM 0223 UTC AND RECENT INFRARED IMAGERY SUGGEST THAT BILL IS UNDERGOING AN EYEWALL REPLACEMENT CYCLE...WITH THE COLDEST CLOUD TOPS CURRENTLY IN THE OUTER CONVECTIVE RING. SATELLITE INTENSITY ESTIMATES REMAIN 90 KT FROM SAB AND 77 KT FROM TAFB. THE INITIAL INTENSITY IS 85 KT...AND THIS COULD BE GENEROUS DUE TO THE EYEWALL REPLACEMENT. THE INITIAL MOTION IS 285/15. BILL IS ON THE SOUTH SIDE OF A LOW/MID-LEVEL RIDGE...WHICH SHOULD STEER THE HURRICANE GENERALLY WEST-NORTHWESTWARD FOR THE NEXT COUPLE OF DAYS. AFTER THAT...THE LARGE-SCALE MODELS FORECAST THE RIDGE TO WEAKEN AS A SERIES OF TROUGHS MOVE THROUGH THE WESTERN ATLANTIC AND THE EASTERN UNITED STATES. ONE MID/UPPER-LEVEL TROUGH IS CURRENTLY NORTHEAST OF BERMUDA...MOVING SOUTHWARD. A SECOND MID/UPPER-LEVEL TROUGH IS ALONG THE EAST COAST OF THE UNITED STATES...FORECAST TO MOVE EASTWARD AND THEN SOUTHWARD. FINALLY...A STRONG DEEP-LAYER TROUGH IS FORECAST TO DEVELOP OVER THE EASTERN UNITED STATES BETWEEN 72-120 HR. ALL TRACK GUIDANCE INDICATES THAT BILL SHOULD TURN NORTHWARD IN RESPONSE TO THE TROUGHS...BUT THERE IS SOME NOTABLE SPREAD IN WHERE AND WHEN. THE ECMWF...GFS...GFS ENSEMBLE MEAN... AND THE BAM MODELS TURN BILL NORTHWARD BETWEEN 62W-65W IN RESPONSE TO THE FIRST TWO TROUGHS. THE REMAINDER OF THE TRACK GUIDANCE CALLS FOR THE NORTHWARD TURN BETWEEN 65W-70W...DUE TO LESS RESPONSE TO THE FIRST TWO TROUGHS AND THE EVENTUAL EFFECT OF THE THIRD TROUGH. THE PREVIOUS FORECAST TRACK WAS IN THE WESTERN CLUSTER... AND THERE IS NO OBVIOUS REASON TO JUMP THE FORECAST TO THE EASTERN CLUSTER. THEREFORE...THE NEW TRACK IS DOWN THE MIDDLE OF THE WESTERN GUIDANCE CLUSTER AND SIMILAR TO THE PREVIOUS FORECAST. BILL IS IN A LIGHT VERTICAL WIND SHEAR ENVIRONMENT...AND THE SEA SURFACE TEMPERATURES INCREASE ALONG THE FORECAST TRACK. THE HURRICANE SHOULD INTENSIFY AFTER THE EYEWALL REPLACEMENT CYCLE IS OVER...WITH ALL GUIDANCE FORECASTING IT TO BECOME A MAJOR HURRICANE. THE INTENSITY FORECAST CALLS FOR A PEAK INTENSITY OF 110 KT IN 48 HR. AFTER 48 HR...THE LARGE-SCALE MODELS FORECAST BILL TO ENCOUNTER MODERATE SOUTHERLY OR SOUTHWESTERLY VERTICAL WIND SHEAR...AND THE INTENSITY FORECAST THUS CALLS FOR GRADUAL WEAKENING DURING THAT TIME. FORECAST POSITIONS AND MAX WINDS INITIAL 18/0900Z 15.5N 49.7W 85 KT 12HR VT 18/1800Z 16.2N 51.7W 90 KT 24HR VT 19/0600Z 17.4N 54.2W 100 KT 36HR VT 19/1800Z 18.9N 56.7W 105 KT 48HR VT 20/0600Z 20.5N 59.0W 110 KT 72HR VT 21/0600Z 24.0N 63.5W 110 KT 96HR VT 22/0600Z 29.5N 67.5W 105 KT 120HR VT 23/0600Z 35.5N 68.0W 100 KT $$ FORECASTER BEVEN |
