Hurricane BILL

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HURRICANE BILL DISCUSSION NUMBER  35
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL032009
1100 PM AST SUN AUG 23 2009
 
BILL STILL HAS STRUCTURAL CHARACTERISTICS OF A TROPICAL CYCLONE...
WITH DEEP CONVECTION NEAR THE CENTER AND A FRAGMENT OF AN EYEWALL
VISIBLE IN MICROWAVE IMAGERY FROM A 2304 UTC SSMIS PASS. BASED ON
THE INNER-CORE STRUCTURE...AND A DVORAK CI NUMBER OF 4.0 FROM TAFB
AT 0000 UTC...BILL IS MAINTAINED AS A 65 KT HURRICANE FOR THIS
ADVISORY.
 
BILL HAS ACCELERATED TOWARD THE EAST-NORTHEAST OVER THE PAST SEVERAL
HOURS...AND THE INITIAL MOTION ESTIMATE IS 060/35. BILL IS EXPECTED
TO REMAIN ON AN EAST-NORTHEASTWARD HEADING UNDER THE INFLUENCE OF
THE MID-LATITUDE WESTERLIES FOR THE NEXT COUPLE OF DAYS...AND THE
TRACK GUIDANCE REMAINS IN EXCELLENT AGREEMENT ON THIS SCENARIO.
AFTER 48 HOURS...BILL WILL SLOW DOWN AND TURN TOWARD THE NORTH AS
IT COMES UNDER THE INFLUENCE OF A MUCH LARGER EXTRATROPICAL CYCLONE
LOCATED SOUTHWEST OF ICELAND. BILL WILL EVENTUALLY BE ABSORBED INTO
THIS LARGER CIRCULATION BY 96 HOURS. THE NEW OFFICIAL FORECAST IS A
LITTLE FASTER THAN THE PREVIOUS PACKAGE...AND IS CLOSE TO THE
MULTI-MODEL CONSENSUS.

BILL IS BEGINNING TO UNDERGO EXTRATROPICAL TRANSITION...WITH THE
UPPER-LEVEL CLOUD PATTERN EXPANDING NORTH AND EAST OF THE CENTER IN
THE ENTRANCE REGION OF A 140-KT UPPER-LEVEL JET CORE CENTERED ALONG
55N. ALSO...DATA FROM A 2226 UTC QUIKSCAT PASS ALONG WITH NUMEROUS
SURFACE OBSERVATIONS SHOW THAT THE WIND FIELD OF BILL HAS BEGUN TO
EXPAND...PARTICULARLY IN THE SOUTHEASTERN QUADRANT. MOST OF THE
GLOBAL MODEL GUIDANCE INDICATES THAT BILL WILL COMPLETE THE
EXTRATROPICAL TRANSITION PROCESS WITHIN 12 TO 24 HOURS. AFTER THAT
TIME...UPPER-LEVEL DIVERGENCE ASSOCIATED WITH THE JET WILL HELP
MAINTAIN BILL AS AN EXTRATROPICAL CYCLONE...AND THE OFFICIAL
INTENSITY FORECAST SHOWS GRADUAL WEAKENING AS BILL MOVES ACROSS THE
NORTHERN ATLANTIC. AS BILL BECOMES FULLY EXTRATROPICAL...THE WIND
FIELD WILL CONTINUE TO EXPAND...ESPECIALLY IN THE SOUTHERN
SEMICIRCLE.
 
LARGE AND DANGEROUS SWELLS ASSOCIATED WITH BILL WILL CONTINUE
IMPACTING THE CANADIAN MARITIMES DURING THE NEXT 12 TO 24 HOURS...
WHILE SWELLS ALONG THE EAST COAST OF THE UNITED STATES WILL CONTINUE
TO SUBSIDE OVERNIGHT.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      24/0300Z 47.1N  55.5W    65 KT
 12HR VT     24/1200Z 49.1N  47.9W    55 KT
 24HR VT     25/0000Z 50.8N  36.0W    45 KT...EXTRATROPICAL
 36HR VT     25/1200Z 52.2N  24.5W    40 KT...EXTRATROPICAL
 48HR VT     26/0000Z 53.5N  14.7W    35 KT...EXTRATROPICAL
 72HR VT     27/0000Z 61.0N   2.0W    30 KT...EXTRATROPICAL
 96HR VT     28/0000Z...DISSIPATED
 
$$
FORECASTER BRENNAN
 
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