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| #289122 (Received by flhurricane at: 10:37 PM 17.Aug.2009) TCDAT3 HURRICANE BILL DISCUSSION NUMBER 11 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL032009 1100 PM AST MON AUG 17 2009 BILL CONTINUES TO SLOWLY STRENGTHEN OVER THE TROPICAL ATLANTIC. THE HURRICANE IS GENERATING VERY DEEP...COLD-TOPPED CONVECTION...THOUGH THERE ARE SOME EVIDENT ASYMMETRIES. SATELLITE PICTURES ALSO REVEAL AN EXPANSIVE CIRRUS CANOPY...SUGGESTIVE OF A WELL-ESTABLISHED UPPER-LEVEL OUTFLOW. EARLIER MICROWAVE PASSES INDICATED AN ABSENCE OF INNER CORE FEATURES...BUT A 2229 SSMIS PASS SUGGESTS THAT BILL MAY BE FINALLY FORMING AN INNER CORE. DVORAK T-NUMBERS ARE 4.5 AND 5.0 FROM TAFB AND SAB...RESPECTIVELY. BASED UPON THESE ESTIMATES... THE INITIAL INTENSITY IS RAISED TO 85 KT. THERE ARE NO OBVIOUS REASONS TO PREVENT BILL FROM INTENSIFYING FURTHER DURING THE SEVERAL DAYS...AS THE INTENSITY GUIDANCE AGREES ON AN ENVIRONMENT CHARACTERIZED BY LOW SHEAR AND WARM SEA SURFACE TEMPERATURES. PERHAPS THE ONLY LIMITING FACTOR WILL BE FLUCTUATIONS WITHIN THE INNER CORE FOR WHICH THERE IS VIRTUALLY NO FORECAST SKILL. THE GUIDANCE IS IN GENERAL AGREEMENT THAT BILL SHOULD REACH A PEAK IN INTENSITY IN ABOUT 72 HOURS. TOWARD THE END OF THE PERIOD...GLOBAL MODELS HAVE BEEN PREDICTING A GRADUAL INCREASE IN SOUTHWESTERLY SHEAR AS BILL BEGINS TO BECOME MORE DISPLACED TO THE NORTH OF AN UPPER-LEVEL ANTICYCLONE. CONSEQUENTLY...THE OFFICIAL FORECAST SHOWS A WEAKENING TREND AFTER 72 HOURS. RECENT CENTER FIXES YIELD AN INITIAL MOTION ESTIMATE OF 285/15. THE FORECAST RATIONALE REMAINS UNCHANGED. A WEAKNESS ALONG 50-55W IS FORECAST TO ERODE A LARGE PORTION OF THE SUBTROPICAL RIDGE OVER THE CENTRAL ATLANTIC BEGINNING AS SOON AS 24 HOURS FROM NOW. AS A RESULT...THE GENERAL WEST-NORTHWESTWARD TRACK THAT BILL HAS MAINTAINED FOR SEVERAL DAYS SHOULD BEGIN TO BEND MORE TOWARD THE NORTHWEST BY 48-72 HOURS. BEYOND 72 HOURS...BILL SHOULD BE STEERED ON A NORTH-NORTHWESTERLY TO NORTHERLY TRACK WHERE IT SHOULD BEGIN ENCOUNTERING THE EFFECTS OF A DIGGING LONGWAVE TROUGH OVER THE EASTERN UNITED STATES. THE OFFICIAL FORECAST IS NOT ALL THAT DIFFERENT FROM THE PREVIOUS ADVISORY PACKAGE...WITH ONLY COSMETIC CHANGES MADE TO THE FORECAST TRACK. THE WIND RADII WERE ADJUSTED SLIGHTLY BASED ON THE MOST RECENT QUIKSCAT OVERPASS. BILL IS FORECAST TO GROW A LITTLE MORE IN SIZE DURING THE FORECAST PERIOD...ALTHOUGH SOME GUIDANCE SUCH AS THE GFS SUGGESTS THAT IT MAY BECOME EVEN LARGER THAN INDICATED IN THE NHC FORECAST. FORECAST POSITIONS AND MAX WINDS INITIAL 18/0300Z 15.0N 48.3W 85 KT 12HR VT 18/1200Z 15.7N 50.3W 95 KT 24HR VT 19/0000Z 16.9N 52.8W 100 KT 36HR VT 19/1200Z 18.1N 55.3W 105 KT 48HR VT 20/0000Z 19.7N 57.8W 110 KT 72HR VT 21/0000Z 23.5N 62.5W 110 KT 96HR VT 22/0000Z 28.5N 66.0W 105 KT 120HR VT 23/0000Z 34.5N 68.5W 100 KT $$ FORECASTER KIMBERLAIN/PASCH |
