Hurricane BILL

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HURRICANE BILL DISCUSSION NUMBER  13
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL032009
1100 AM AST TUE AUG 18 2009
 
VISIBLE SATELLITE IMAGES REVEAL A VERY SYMMETRIC HURRICANE WITH
OUTFLOW WELL ESTABLISHED IN ALL QUADRANTS.  THE EYE OF BILL IS
QUITE LARGE...MEASURING ABOUT 35-40 NM IN DIAMETER.  SUBJECTIVE
DVORAK INTENSITY ESTIMATES ARE NOW T5.0 FROM BOTH TAFB AND SAB...
AND THE INITIAL INTENSITY IS INCREASED TO 90 KT.  A HURRICANE
HUNTER AIRCRAFT THAT WAS ORIGINALLY SCHEDULED TO INVESTIGATE THE
REMNANTS OF ANA HAS BEEN TASKED TO FLY INTO BILL THIS AFTERNOON.
DATA FROM THE AIRCRAFT WILL PROVIDE A BETTER ASSESSMENT OF THE
INTENSITY AND SIZE OF THE HURRICANE.
 
THE INITIAL MOTION IS 285/14.  BILL IS CURRENTLY BEING STEERED
WEST-NORTHWESTWARD BY THE SUBTROPICAL RIDGE TO THE NORTH OF THE
HURRICANE.  A COUPLE OF TROUGHS SEEN IN WATER VAPOR IMAGERY TO THE
NORTH AND NORTHWEST OF THE HURRICANE ARE FORECAST TO WEAKEN THE
RIDGE DURING THE NEXT COUPLE OF DAYS.  THIS SHOULD ALLOW BILL TO
TURN NORTHWESTWARD AND THE MODELS ARE IN GOOD AGREEMENT ON THIS
SCENARIO DURING THROUGH 48 HOURS.  AFTER THAT...A LARGE MID-LATITUDE
TROUGH IS FORECAST BY THE GLOBAL MODELS TO
MOVE INTO THE EASTERN UNITED STATES ON DAY 4 AND 5.  THE MODELS
RESPOND BY TURNING THE HURRICANE NORTHWARD AT THAT TIME...HOWEVER
THERE REMAINS SOME SPREAD AS TO WHEN AND WHERE THAT WILL OCCUR.
AS BEFORE...THE GFS AND ECMWF REMAIN ON THE RIGHT SIDE OF THE
MODEL ENVELOPE...WHILE THE UKMET AND HWRF ARE ON THE LEFT.  THE
OFFICIAL FORECAST IS VERY SIMILAR TO THE PREVIOUS NHC TRACK AND
NEAR THE MIDDLE OF THE GUIDANCE ENVELOPE THROUGH 72 HOURS.
THEREAFTER...THE NEW TRACK HAS BEEN SHIFTED EASTWARD...BUT REMAINS
TO THE WEST OF THE MODEL CONSENSUS.
 
BILL IS IN A CONDUCIVE ATMOSPHERIC ENVIRONMENT FOR STRENGTHENING
AND SSTS ALONG THE FORECAST TRACK WILL BE INCREASING DURING THE
NEXT COUPLE OF DAYS.  THE INTENSITY FORECAST SHOWS GRADUAL
STRENGTHENING AND TOPS OUT AT 110 KT...WHICH IS CLOSE TO THE
CONSENSUS OF THE INTENSITY GUIDANCE.  LATER IN THE FORECAST
PERIOD...MODERATE SOUTH TO SOUTHWESTERLY WIND SHEAR IS EXPECTED TO
INCREASE...AND THE OFFICIAL FORECAST PREDICTS GRADUAL WEAKENING AT
THAT TIME.
 
THE WIND RADII WERE EXPENDED OUTWARD BASED ON AN EARLIER QUIKSCAT
PASS.
  
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      18/1500Z 15.9N  51.2W    90 KT
 12HR VT     19/0000Z 16.8N  53.0W    95 KT
 24HR VT     19/1200Z 18.0N  55.3W   105 KT
 36HR VT     20/0000Z 19.6N  57.7W   110 KT
 48HR VT     20/1200Z 21.5N  60.3W   110 KT
 72HR VT     21/1200Z 25.9N  64.7W   110 KT
 96HR VT     22/1200Z 31.5N  67.5W   105 KT
120HR VT     23/1200Z 38.0N  66.5W    95 KT
 
$$
FORECASTER BROWN/CANGIALOSI
 
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