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Hurricane BILL (Text)

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HURRICANE BILL DISCUSSION NUMBER  21
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL032009
1100 AM AST THU AUG 20 2009
 
CONVENTIONAL SATELLITE...MICROWAVE IMAGES AND NUMEROUS OBSERVATIONS
FROM A NOAA P-3 RESEARCH PLANE INDICATE THAT BILL HAS WEAKENED A
LITTLE BIT DURING THE PAST SEVERAL HOURS.  DVORAK T-NUMBERS HAVE
DECREASED SINCE YESTERDAY...THE EYEWALL HAS BECOME OPEN TO THE
SOUTHWEST AND THE MAXIMUM FLIGHT LEVEL AND SFMR WINDS WERE 121 AND
93 KNOTS...RESPECTIVELY...EARLIER THIS MORNING. IN FACT...SOME ARC
CLOUDS ARE MOVING AWAY FROM THE HURRICANE SUGGESTING THAT BILL IS
NOT STRENGTHENING AT THIS TIME.  BASED ON THESE DATA...THE INITIAL
INTENSITY HAS BEEN REDUCED TO 105 KNOTS...AND THIS IS PROBABLY ON
THE HIGH SIDE.  THE LARGE SCALE ENVIRONMENT IS CONDUCIVE FOR
REINTENSIFICATION SINCE BILL IS ABOUT TO ENCOUNTER THE WARMEST
WATERS ALONG ITS PATH SO FAR...AND THE SHEAR IS FORECAST TO BE
QUITE LIGHT.  HOWEVER...MOST OF THE INTENSITY CHANGE COULD BE
ASSOCIATED WITH EYEWALL REPLACEMENT CYCLES. THE OFFICIAL FORECAST
CALLS FOR RESTRENGTHENING AND BILL IS EXPECTED TO REACH CATEGORY
FOUR AGAIN IN A DAY OR SO.  THEREAFTER...THE HURRICANE SHOULD
GRADUALLY BEGIN TO INTERACT WITH A MID-LATITUDE TROUGH AND BY 96
HOURS IT SHOULD BE IN EXTRATROPICAL TRANSITION AND BE FULLY
EXTRATROPICAL IN FIVE DAYS.
 
BILL HAS CONTINUED TO MOVE ON A STEADY NORTHWEST TRACK OR 305
DEGREES AT 16 KNOTS...EMBEDDED WITHIN THE FLOW SURROUNDING THE
AZORES-BERMUDA HIGH.  IN ABOUT TWO DAYS...THE HURRICANE WILL BECOME
STEERED NORTHWARD AND THEN NORTHEASTWARD BY THE FLOW BETWEEN A
LARGE MID-LATITUDE TROUGH SWINGING EASTWARD ACROSS THE EASTERN
UNITED STATES AND THE SUBTROPICAL HIGH. ONCE THE RECURVATURE
BEGINS...THE HURRICANE SHOULD INCREASE IN FORWARD SPEED. MOST OF
THE TRACK GUIDANCE SHIFTED SLIGHTLY TO THE WEST COMPARED TO THE
PREVIOUS RUN. THIS SHIFT IN GUIDANCE JUSTIFIES A VERY SMALL SHIFT
TO THE WEST OF THE TRACK OFFICIAL FORECAST...WHICH INDEED IS VERY
CLOSE TO THE CONSENSUS.
 
LARGE SWELLS GENERATED BY THIS HURRICANE ARE AFFECTING THE NORTHERN
LEEWARD ISLANDS AND SHOULD BEGIN AFFECTING THE BAHAMAS...BERMUDA...
MOST OF THE EASTERN U.S. COAST...AND THE ATLANTIC MARITIMES OF
CANADA DURING THE NEXT FEW DAYS.  THESE SWELLS WILL LIKELY
CAUSE EXTREMELY DANGEROUS SURF AND LIFE-THREATENING RIP CURRENTS.
PLEASE CONSULT STATEMENTS ISSUED BY YOUR LOCAL WEATHER OFFICE FOR
MORE DETAILS.
 
THIS AFTERNOON NOAA AND THE 53RD HURRICANE HUNTERS WILL BE
CONDUCTING A TWO-AIRCRAFT SYNOPTIC SURVEILLANCE MISSION AROUND
HURRICANE BILL TO IMPROVE THE INITIAL ANALYSIS FOR THE NUMERICAL
MODELS.

 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      20/1500Z 22.6N  61.7W   105 KT
 12HR VT     21/0000Z 24.2N  63.8W   110 KT
 24HR VT     21/1200Z 26.6N  66.0W   115 KT
 36HR VT     22/0000Z 29.5N  67.5W   115 KT
 48HR VT     22/1200Z 32.5N  69.0W   110 KT
 72HR VT     23/1200Z 40.5N  66.5W   100 KT
 96HR VT     24/1200Z 48.0N  53.0W    65 KT...BECOMING EXTRATROPICAL
120HR VT     25/1200Z 55.0N  28.0W    50 KT...EXTRATROPICAL
 
$$
FORECASTER AVILA
 
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