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Hurricane BILL


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HURRICANE BILL DISCUSSION NUMBER  18
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL032009
500 PM AST WED AUG 19 2009
 
VISIBLE SATELLITE IMAGES SHOW THAT BILL IS AN IMPRESSIVE HURRICANE
WITH MESOCYCLONES NOTED IN THE EYE...CURVED BANDING FEATURES IN ALL
QUADRANTS AND A WELL-ESTABLISHED OUTFLOW PATTERN.  AN FORCE RESERVE
HURRICANE HUNTER RECENTLY MEASURED 135 KT AT 700 MB...ALONG WITH
SFMR WINDS OF 103 KT AND A MINIMUM PRESSURE OF 947 MB. IN
ADDITION...THERE WAS AN SFMR MEASUREMENT OF 106 KT FROM THE NOAA
MISSION THIS MORNING.  SATELLITE CLASSIFICATION ARE 127 KT FROM
TAFB/SAB AND THE INITIAL INTENSITY IS KEPT AT 115 KT AS A
COMPROMISE OF ALL THESE DATA.

VERY WARM WATERS ARE ALONG THE PATH OF THE HURRICANE FOR THE NEXT
FEW DAYS.  THE BIGGEST QUESTION IS WHETHER THE UPPER ENVIRONMENT
WILL REMAIN FAVORABLE FOR STRENGTHENING.   A PAIR OF UPPER-LEVEL
TROUGHS HAVE THE POTENTIAL TO INDUCE SOME SHEAR ON BILL...ONE ALONG
60W AND OTHER AT ABOUT 70W.  WHILE THE MODELS DISAGREE ON WHETHER
THE FIRST TROUGH WILL AFFECT THE HURRICANE MUCH...MOST MODELS SHOW
SOUTHWESTERLY SHEAR INCREASING IN A COUPLE DAYS AS A RESULT OF THE
SECOND FEATURE.  IN ADDITION...AN EYEWALL REPLACEMENT CYCLE COULD
OCCUR AT ANY TIME WITH A SECONDARY WIND MAXIMUM NOTED AT ABOUT 75 N
MI FROM THE CENTER IN AIRCRAFT DATA.  REGARDLESS...ALL OF THE
RELIABLE MODELS KEEP THE HURRICANE QUITE STRONG FOR THE NEXT
SEVERAL DAYS...AND THE OFFICIAL INTENSITY FORECAST REFLECTS THAT
LIKELIHOOD.  
 
THE ESTIMATED MOTION IS A LITTLE MORE TO THE RIGHT AND FASTER...NOW
305/17.  STRONG SUBTROPICAL RIDGING SHOULD KEEP BILL ON THIS
GENERAL TRACK FOR THE NEXT COUPLE OF DAYS WITH A GRADUAL BEND TOWARD
THE NORTH-NORTHWEST BY THE WEEKEND AS THE HURRICANE MOVES INTO A
BREAK IN THE RIDGE.  SOME OF THE MODELS...SUCH AS THE GFS...NOW
SHOW A SLIGHTLY STRONGER RIDGE OVER THE WESTERN ATLANTIC AND A
SLOWER MID-LATITUDE TROUGH MOVING ACROSS THE EASTERN UNITED STATES. 
IF THIS SOLUTION IS CORRECT...BILL WOULD BE ABLE TO MOVE A LITTLE
FARTHER TO THE WEST BEFORE TURNING TO THE NORTH AND NORTHEAST. 
THERE HAS BEEN A SMALL WESTWARD SHIFT IN MOST OF THE AFTERNOON
MODEL GUIDANCE...AND THE OFFICIAL FORECAST IS SHIFTED IN THAT
DIRECTION.  THIS IS A GOOD TIME TO POINT OUT THAT THERE IS A LOT OF
UNCERTAINTY IN THE LONG-RANGE TROPICAL CYCLONE FORECAST AND ONE
SHOULD NOT FOCUS ON THE EXACT TRACK AT THOSE TIME PERIODS.  

BECAUSE BILL IS A LARGE AND STRONG HURRICANE...SWELLS TRIGGERED BY
THE HURRICANE SHOULD AFFECT THE NORTHERN LEEWARD ISLANDS...THE
BAHAMAS...BERMUDA AND MOST OF THE EASTERN UNITED STATES 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.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      19/2100Z 19.8N  57.6W   115 KT
 12HR VT     20/0600Z 21.1N  59.7W   120 KT
 24HR VT     20/1800Z 23.0N  62.4W   125 KT
 36HR VT     21/0600Z 25.2N  64.6W   120 KT
 48HR VT     21/1800Z 27.9N  66.6W   120 KT
 72HR VT     22/1800Z 34.0N  69.0W   110 KT
 96HR VT     23/1800Z 42.0N  65.5W    95 KT
120HR VT     24/1800Z 51.5N  50.5W    55 KT...EXTRATROPICAL
 
$$
FORECASTER BLAKE
 
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