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| #289049 (Received by flhurricane at: 4:34 PM 17.Aug.2009) TCDAT3 HURRICANE BILL DISCUSSION NUMBER 10 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL032009 500 PM AST MON AUG 17 2009 BILL IS BEGINNING TO SHOW SIGNS OF DEVELOPING INNER CORE FEATURES... WITH HINTS OF AN EYE FORMING IN RECENT SATELLITE IMAGERY AND EXPANDING COLD CLOUD TOPS AROUND THE CENTER. DVORAK T-NUMBERS WERE 4.5 FROM SAB AND TAFB AT 1800 UTC...AND THE INITIAL INTENSITY IS HELD AT 80 KT FOR THIS PACKAGE. BILL PASSED JUST TO THE NORTH OF NOAA BUOY 40141 THIS AFTERNOON...WHICH REPORTED A MINIMUM PRESSURE OF 972 MB AT 1800 UTC WITH A PEAK 1-MINUTE WIND OF 51 KT. BASED ON THESE DATA...THE CENTRAL PRESSURE ESTIMATE IS REDUCED TO 969 MB. THE INTENSITY FORECAST IS UNCHANGED FROM THE PREVIOUS PACKAGE. THE ENVIRONMENT AROUND THE CYCLONE APPEARS FAVORABLE FOR INTENSIFICATION. OCEAN TEMPERATURES INCREASE ALONG THE TRACK...AND THE GFS AND ECMWF BOTH SHOW AN UPPER-LEVEL ANTICYCLONE DEVELOPING OVER THE SYSTEM. AS WAS THE CASE EARLIER...THE SHIPS AND LGEM SHOW A BROAD PEAK IN INTENSITY IN 2 OR 3 DAYS...WHILE THE HWRF AND GFDL SHOW ARE STRONGER LATER IN THE PERIOD. THE OFFICIAL FORECAST REMAINS UNCHANGED FROM THE PREVIOUS ADVISORY...PEAKING A LITTLE HIGHER THAN THE SHIPS AND LGEM BEFORE SHOWING SOME WEAKENING AT DAY 5. THE INITIAL MOTION ESTIMATE IS 285/14. THE TRACK MODEL GUIDANCE IS IN EXCELLENT AGREEMENT THROUGH 48 HOURS...AND THROUGH THAT TIME THE OFFICIAL FORECAST IS SIMPLY AN EXTENSION OF THE PREVIOUS PACKAGE. BEYOND THAT TIME ALMOST ALL OF THE TRACK GUIDANCE HAS SHIFTED TO THE LEFT....WITH THE EXCEPTION OF THE UKMET...WHICH HAS FINALLY TRENDED TOWARD A RECURVATURE SCENARIO. ALL OF THE GLOBAL MODELS NOW SHOW BILL INTERACTING WITH A LARGE MID TO UPPER-LEVEL TROUGH CENTERED OVER THE EASTERN UNITED STATES BY THE END OF THE PERIOD...HOWEVER THERE ARE DIFFERENCES IN THE AMPLITUDE AND SPEED OF THE TROUGH THAT WILL BE CRUCIAL TO WHEN AND WHERE BILL RECURVES. INTERESTINGLY...THE GFS AND ECMWF ARE IN EXCELLENT AGREEMENT AT 5 DAYS...BUT NOW LIE ON THE EASTERN EDGE OF THE GUIDANCE ENVELOPE... WITH THE GFS ENSEMBLE MEAN EVEN FARTHER EAST. GIVEN THE SPREAD IN THE GUIDANCE...THE OFFICIAL FORECAST IS SHIFTED ONLY SLIGHTLY TO THE LEFT OF THE PREVIOUS PACKAGE AT DAYS 3 THROUGH 5...AND LIES BETWEEN THE TVCN MULTI-MODEL CONSENSUS AND THE ECMWF/GFS BLEND. THIS IS A GOOD TIME TO EMPHASIZE THE UNCERTAINTY THAT EXISTS IN TRACK FORECASTING IN THE 3 TO 5 DAY PERIOD...WHERE AVERAGE NHC TRACK ERRORS ARE TYPICALLY SEVERAL HUNDRED MILES. FORECAST POSITIONS AND MAX WINDS INITIAL 17/2100Z 14.6N 46.7W 80 KT 12HR VT 18/0600Z 15.2N 48.7W 90 KT 24HR VT 18/1800Z 16.2N 51.3W 95 KT 36HR VT 19/0600Z 17.4N 53.8W 100 KT 48HR VT 19/1800Z 18.8N 56.4W 105 KT 72HR VT 20/1800Z 22.5N 61.0W 110 KT 96HR VT 21/1800Z 27.0N 65.0W 110 KT 120HR VT 22/1800Z 33.1N 67.5W 105 KT $$ FORECASTER BRENNAN/ROBERTS |
