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| #289380 (Received by flhurricane at: 4:46 AM 19.Aug.2009) TCDAT3 HURRICANE BILL DISCUSSION NUMBER 16 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL032009 500 AM AST WED AUG 19 2009 BILL HAS A WELL-DEFINED 25-30 N MI WIDE EYE WITH EYEWALL CLOUD TOPS TO NEAR -80C. SATELLITE INTENSITY ESTIMATES FROM TAFB AND SAB WERE 115 KT AT 06Z...AND THE CURRENT SATELLITE SIGNATURE SUGGESTS A SLIGHTLY STRONGER SYSTEM. BASED ON THE SATELLITE ESTIMATES...THE INITIAL INTENSITY IS INCREASED TO 115 KT. A NOAA HURRICANE HUNTER AIRCRAFT IS CURRENTLY ENROUTE TO INVESTIGATE BILL. THE MOTION IS WOBBLING BETWEEN 295-300 DEGREES AT 14 KT. BILL IS ON THE SOUTHWEST SIDE OF THE ATLANTIC SUBTROPICAL RIDGE. WATER VAPOR IMAGERY SHOWS A MID/UPPER-LEVEL LOW NEAR 32N60W AND A MID/UPPER- LEVEL TROUGH N OF 30N BETWEEN 69W-75W. THESE FEATURES ARE CURRENTLY CREATING A WEAKNESS IN THE WESTERN PORTION OF THE SUBTROPICAL RIDGE. THE TRACK GUIDANCE MODELS FORECAST BILL TO GRADUALLY TURN NORTHWESTWARD TOWARDS THIS WEAKNESS DURING THE NEXT 48-72 HR...WITH THE ECMWF SHOWING THE EARLIEST TURN AND THE NOGAPS/UKMET SHOWING THE LATEST TURN. AFTER THAT...A LARGE DEEP-LAYER TROUGH MOVING INTO THE EASTERN UNITED STATES SHOULD CAUSE BILL TO RECURVE NORTHWARD AND NORTHEASTWARD. THERE IS A LARGE MODEL SPREAD IN BOTH DIRECTION AND SPEED AFTER 72 HR...WITH THE NOGAPS ON ONE SIDE BRINGING BILL NEAR NEW ENGLAND AND THE CORRECTED CONSENSUS MODELS ON THE OTHER SIDE CALLING FOR A SHARP TURN OUT TO SEA. OVERALL...THE ENVELOPE OF MODEL GUIDANCE HAS SHIFTED A LITTLE TO THE WEST...SO THE NEW OFFICIAL FORECAST WILL DO LIKEWISE. THE NEW FORECAST TRACK IS NEAR THE MODEL CONSENSUS AND THE MIDDLE OF THE GUIDANCE ENVELOPE. BILL HAS STRENGTHENED IN SPITE OF BEING IN AN ENVIRONMENT OF 10-15 KT OF SOUTHWESTERLY VERTICAL WIND SHEAR. THE LARGE-SCALE MODELS FORECAST THIS SHEAR SHOULD DECREASE AFTER 12 HR...SO ADDITIONAL STRENGTHENING IS FORECAST. BY 48-72 HR...BILL SHOULD INTERACT WITH THE UPPER-LEVEL TROUGH CURRENTLY JUST OFF THE NORTH CAROLINA COAST. THIS IS LIKELY TO CAUSE ANOTHER ROUND OF SHEAR...SO THE INTENSITY FORECAST CALLS FOR SLOW WEAKENING DURING THAT TIME. AFTER 72 HR...BILL SHOULD BECOME EMBEDDED IN THE WESTERLIES AS IT MOVES OVER COLDER SEA SURFACE TEMPERATURES...AND A FASTER WEAKENING IS EXPECTED. IT SHOULD BE NOTED THAT EYEWALL REPLACEMENT CYCLES... WHICH ARE VERY DIFFICULT TO ANTICIPATE...MAY PRODUCE SOME FLUCTUATIONS IN INTENSITY SUPERIMPOSED ON THE GENERAL TREND OF THE INTENSITY FORECAST. FORECAST POSITIONS AND MAX WINDS INITIAL 19/0900Z 18.0N 54.9W 115 KT 12HR VT 19/1800Z 19.0N 56.8W 120 KT 24HR VT 20/0600Z 20.6N 59.4W 125 KT 36HR VT 20/1800Z 22.5N 62.0W 125 KT 48HR VT 21/0600Z 24.4N 64.4W 120 KT 72HR VT 22/0600Z 29.5N 68.0W 115 KT 96HR VT 23/0600Z 36.0N 68.5W 100 KT 120HR VT 24/0600Z 44.0N 62.0W 80 KT $$ FORECASTER BEVEN |
