000
WTNT43 KNHC 191445
TCDAT3
HURRICANE BILL DISCUSSION NUMBER  17
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL032009
1100 AM AST WED AUG 19 2009
 
A NOAA P-3 PLANE ON A RESEARCH MISSION HAS BEEN PROVIDING EXCELLENT
DATA FROM BILL DURING THE PAST SEVERAL HOURS. THERE WAS A PEAK
FLIGHT-LEVEL WIND OF 132 KNOTS TWO HOURS AGO AND THE SFMR REPORTED
PEAK WINDS AROUND 105 KNOTS. DATA FROM THE PLANE ALSO SHOW THAT
BILL HAS A LARGE WIND FIELD AND A 30 NMI WIDE EYE. THE LATEST
EXTRAPOLATED MINIMUM CENTRAL PRESSURE WAS 950 MB. ALTHOUGH THE RING
OF DEEP CONVECTION SURROUNDING THE EYE OBSERVED ON SATELLITE HAS
WEAKENED DURING THE PAST COUPLE OF HOURS...THE T-NUMBERS REMAIN
AROUND 6.0 ON THE DVORAK SCALE. INITIAL INTENSITY IS KEPT AT 115 KT
IN THIS ADVISORY. THE LARGE SCALE ENVIRONMENT IS FAVORABLE FOR
ADDITIONAL INTENSIFICATION SINCE BILL IS HEADING FOR A WARMER OCEAN
AND THE SHEAR IS EXPECTED TO BE LOW FOR THE NEXT TWO TO THREE DAYS.
HOWEVER...MOST LIKELY THERE WILL BE FLUCTUATIONS IN INTENSITY IN
THIS PERIOD CONTROLLED BY EYEWALL REPLACEMENT CYCLES. BEYOND 72
HOURS...THE OCEAN IS COOLER AND A GRADUAL WEAKENING SHOULD BEGIN...
BUT BILL IS FORECAST TO REMAIN A HURRICANE THROUGH FIVE DAYS.     

THERE HAS BEEN NO CHANGE IN THE STEERING CURRENTS AND BILL CONTINUES
TO MOVE TOWARD THE WEST-NORTHWEST OR 300 DEGREES AT 16 KNOTS AROUND
THE AZORES-BERMUDA HIGH. THIS GENERAL MOTION SHOULD CONTINUE FOR A
COUPLE OF DAYS. THEREAFTER...A LARGE MID-LATITUDE TROUGH IS
EXPECTED TO SWING EASTWARD OVER THE EASTERN UNITED STATES...FORCING
BILL TO TURN NORTHWARD A GOOD DISTANCE AWAY FROM THE U.S. EAST
COAST. THIS IS IN AGREEMENT WITH THE SOLUTION PROVIDED BY MOST OF
THE DYNAMICAL MODELS...WHICH IN FACT HAVE BEEN QUITE CONSISTENT IN
TURNING BILL NORTHWARD FOR THE PAST SEVERAL RUNS. THE OFFICIAL
FORECAST IS VERY SIMILAR TO THE PREVIOUS ONE AND IS VERY CLOSE TO
THE MODEL CONSENSUS.

BECAUSE BILL IS A LARGE AND STRONG HURRICANE...SWELLS TRIGGERED BY
THE HURRICANE SHOULD AFFECT THE NORTHERN LEEWARD ISLANDS...BERMUDA
AND PORTIONS OF THE EASTERN UNITED STATES DURING THE NEXT FEW DAYS.  
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      19/1500Z 18.7N  56.3W   115 KT
 12HR VT     20/0000Z 19.9N  58.3W   120 KT
 24HR VT     20/1200Z 21.7N  61.0W   125 KT
 36HR VT     21/0000Z 23.5N  63.5W   125 KT
 48HR VT     21/1200Z 26.0N  65.5W   120 KT
 72HR VT     22/1200Z 32.0N  68.5W   115 KT
 96HR VT     23/1200Z 38.5N  67.0W   100 KT
120HR VT     24/1200Z 47.0N  58.0W    75 KT
 
$$
FORECASTER AVILA