000
WTNT43 KNHC 200246
TCDAT3
HURRICANE BILL DISCUSSION NUMBER  19
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL032009
1100 PM AST WED AUG 19 2009
 
DATA FROM A NOAA AIRCRAFT FLYING A RESEARCH MISSION INTO BILL
INDICATE THAT IT IS MAINTAINING ITS INTENSITY.  THE AIRCRAFT
REPORTED PEAK 700 MB FLIGHT-LEVEL WINDS OF 140 KT...AND
A DROPSONDE RELEASED IN THE NORTHEASTERN EYEWALL MEASURED A MEAN
WIND OF 134 KT OVER THE THE LOWEST 150 METERS OF SOUNDING.  THE
SFMR MEASURED A PEAK SURFACE WINDS OF 108 KT.  USING A BLEND OF
THESE DATA SUPPORT A 115 KT INTENSITY FOR THIS ADVISORY.
 
BILL IS MOVING NORTHWESTWARD OR 305/15.  THE SUBTROPICAL RIDGE TO
THE NORTH OF THE HURRICANE IS EXPECTED TO KEEP IT ON THIS GENERAL
COURSE DURING THE NEXT DAY OR SO.  THEREAFTER...A BREAK IN THE
RIDGE IS FORECAST TO DEVELOP OVER THE WESTERN ATLANTIC...AND BILL
SHOULD BEGIN TO TURN NORTHWARD AHEAD OF A STRONG MID-LATITUDE
TROUGH THAT IS FORECAST TO MOVE INTO THE EASTERN UNITED STATES
BY THE WEEKEND.  OVERALL...THE TRACK MODELS HAVE SHOWN GOOD
CONSISTENCY DURING THE LAST DAY OR TWO...AND SO HAS THE OFFICIAL
FORECAST WHICH REMAINS NEAR THE CENTER OF THE TIGHTLY CLUSTERED
GUIDANCE.  THE NEW NHC TRACK FORECAST IS VERY SIMILAR TO THE
PREVIOUS ADVISORY THROUGH 72 HOURS...AND ONLY A SLIGHT WESTWARD
ADJUSTMENT WAS REQUIRED THEREAFTER.  IT IS IMPORTANT TO REMEMBER
THAT FORECAST UNCERTAINTY EXISTS IN THE LONGER RANGES...SO ONE
SHOULD NOT FOCUS ON THE EXACT FORECAST TRACK.
 
BILL IS PREDICTED TO REMAIN OVER WARM WATER FOR THE NEXT COUPLE OF
DAYS.  AN UPPER-LEVEL TROUGH SEEN IN WATER VAPOR IMAGERY ALONG 70W
MAY CAUSE IN INCREASE IN SOUTHWESTERLY UPPER-LEVEL WINDS OVER THE
HURRICANE IN A COUPLE OF DAYS.  HOWEVER...THE SHIPS MODEL SHOWS
THAT THE SHEAR WILL GENERALLY REMAIN LIGHT AND THE INTENSITY
GUIDANCE KEEPS THE HURRICANE STRONG DURING THE NEXT FEW DAYS.
AFTER 72 HOURS...INCREASING SOUTHWESTERLY UPPER-LEVEL FLOW AHEAD OF
THE STRONG TROUGH AND COOLING SSTS SHOULD IMPART A MORE RAPID RATE
OF WEAKENING.  THE GLOBAL MODELS SHOW BILL BEGINNING TO INTERACT
WITH A BAROCLINIC ZONE BY 96 HOURS...SO THE CYCLONE COULD BECOME
EXTRATROPICAL A LITTLE SOONER THAN INDICATED HERE.
 
LARGE SWELLS GENERATED BY THIS HURRICANE WILL AFFECT THE NORTHERN
LEEWARD ISLANDS...THE BAHAMAS...BERMUDA AND MOST OF THE EASTERN
U.S. COAST 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      20/0300Z 20.7N  58.9W   115 KT
 12HR VT     20/1200Z 22.1N  60.9W   120 KT
 24HR VT     21/0000Z 24.1N  63.4W   125 KT
 36HR VT     21/1200Z 26.6N  65.6W   120 KT
 48HR VT     22/0000Z 29.4N  67.5W   120 KT
 72HR VT     23/0000Z 36.0N  69.0W   105 KT
 96HR VT     24/0000Z 45.0N  62.5W    75 KT...INLAND
120HR VT     25/0000Z 53.0N  44.5W    55 KT...EXTRATROPICAL
 
$$
FORECASTER BROWN/PASCH