Hurricane BILL

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HURRICANE BILL DISCUSSION NUMBER  10...CORRECTED
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL032009
500 PM AST MON AUG 17 2009

CORRECTED BUOY ID TO 41041
 
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 41041 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
 
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