Blogging About Hurricane Bill #1

000
WTNT33 KNHC 172032
TCPAT3
BULLETIN
HURRICANE BILL ADVISORY NUMBER 10
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL032009
500 PM AST MON AUG 17 2009

...BILL HEADING WEST-NORTHWESTWARD...LITTLE CHANGE IN STRENGTH...

AT 500 PM AST...2100 UTC...THE CENTER OF HURRICANE BILL WAS LOCATED
NEAR LATITUDE 14.6 NORTH...LONGITUDE 46.7 WEST OR ABOUT 975 MILES...
1570 KM...EAST OF THE LESSER ANTILLES.

BILL IS MOVING TOWARD THE WEST-NORTHWEST NEAR 16 MPH...26 KM/HR...
AND THIS MOTION IS EXPECTED TO CONTINUE FOR THE NEXT COUPLE OF DAYS.

MAXIMUM SUSTAINED WINDS ARE NEAR 90 MPH...150 KM/HR...WITH HIGHER
GUSTS. SOME STRENGTHENING IS FORECAST DURING THE NEXT 48
HOURS...AND BILL COULD BECOME A MAJOR HURRICANE BY WEDNESDAY.

HURRICANE FORCE WINDS EXTEND OUTWARD UP TO 30 MILES...45 KM...FROM
THE CENTER...AND TROPICAL STORM FORCE WINDS EXTEND OUTWARD UP TO 145
MILES...230 KM.

THE ESTIMATED MINIMUM CENTRAL PRESSURE BASED ON DATA FROM NOAA BUOY
41041 IS 969 MB...28.61 INCHES.

...SUMMARY OF 500 PM AST INFORMATION...
LOCATION...14.6N 46.7W
MAXIMUM SUSTAINED WINDS...90 MPH
PRESENT MOVEMENT...WEST-NORTHWEST OR 285 DEGREES AT 16 MPH
MINIMUM CENTRAL PRESSURE...969 MB

THE NEXT ADVISORY WILL BE ISSUED BY THE NATIONAL HURRICANE CENTER AT
1100 PM AST.

$$
FORECASTER ROBERTS/BRENNAN

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000
WTNT43 KNHC 172101
TCDAT3
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