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Hurricane BILL


ZCZC MIATCDAT3 ALL
TTAA00 KNHC DDHHMM
HURRICANE BILL DISCUSSION NUMBER  28
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL032009
500 AM AST SAT AUG 22 2009

REPORTS FROM AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT INDICATE
THAT BILL HAS JUST ABOUT FINISHED ITS EYEWALL REPLACEMENT CYCLE...
AND NOW HAS A 48 N MI WIDE EYE.  THE AIRCRAFT ENCOUNTERED 120 KT
FLIGHT-LEVEL WINDS AT 700 MB IN THE NORTHEASTERN EYEWALL...AND A
DROPSONDE IN THE AREA SUGGESTS SURFACE WINDS OF 90 KT.  THE MINIMUM
CENTRAL PRESSURE WAS 960 MB.  BASED ON THIS DATA...THE INITIAL
INTENSITY REMAINS 90 KT.  THE CIRRUS OUTFLOW IS GOOD IN THE
NORTHWESTERN SEMICIRCLE AND POOR ELSEWHERE.

BILL HAS MOVED A LITTLE TO THE LEFT OF THE PREVIOUS FORECAST...WITH
AN INITIAL MOTION OF 345/19.  OTHER THAN THAT...THERE IS LITTLE
CHANGE IN THE FORECAST PHILOSOPHY OR THE TRACK FORECAST GUIDANCE. 
BILL IS EXPECTED TO RECURVE INTO THE WESTERLIES DURING THE NEXT
24-48 HR BETWEEN A LARGE DEEP-LAYER TROUGH OVER THE EASTERN UNITED
STATES AND A RIDGE OVER THE CENTRAL ATLANTIC.  AFTER 48 HR...THE
SYSTEM SHOULD MOVE QUICKLY EASTWARD IN THE WESTERLIES.  THE NEW
FORECAST TRACK IS SLIGHTLY NORTH AND WEST OF THE PREVIOUS TRACK FOR
THE FIRST 48 HR DUE TO THE INITIAL POSITION AND MOTION.  AFTER THAT
TIME...THE TRACK IS SHIFTED SOUTHWARD FROM THE PREVIOUS TRACK.  THE
NEW FORECAST IS DOWN THE MIDDLE OF THE DYNAMICAL GUIDANCE ENVELOPE.

BILL SHOULD REMAIN IN LIGHT VERTICAL WIND SHEAR AND OVER WARM SEA
SURFACE TEMPERATURES FOR THE NEXT 12-24 HOURS...AND THUS THE
INTENSITY FORECAST CALLS FOR SOME STRENGTHENING DURING THIS TIME. 
AFTER 24 HR...COLDER SSTS AND INCREASING SHEAR SHOULD CAUSE BILL TO
WEAKEN.  EXTRATROPICAL TRANSITION IS EXPECTED TO BEGIN AT ABOUT
THE 48 HR PERIOD AND BE COMPLETE BY 72 HR...AND THE EXTRATROPICAL
REMNANTS OF BILL ARE FORECAST TO GRADUALLY WEAKEN AS THEY CROSS THE
ATLANTIC.

LARGE SWELLS GENERATED BY BILL ARE BEGINNING TO ARRIVE ALONG THE
EAST COAST OF THE UNITED STATES. THESE SWELLS WILL SPREAD NORTHWARD
OVER THE WEEKEND...CAUSING EXTREMELY DANGEROUS SURF AND
LIFE-THREATENING RIP CURRENTS. PLEASE CONSULT STATEMENTS ISSUED BY
YOUR LOCAL WEATHER OFFICE AND METEOROLOGICAL SERVICES FOR MORE
DETAILS.

THE WESTWARD SHIFT IN THE FORECAST TRACK REQUIRES A TROPICAL STORM
WARNING FOR PORTIONS OF THE MASSACHUSETTS COAST...AND THE WIND
SPEED PROBABILITY PRODUCT NOW SHOWS A 40 PERCENT CHANCE OF
TROPICAL-STORM-FORCE WINDS IN THAT AREA.  ANY ADDITIONAL TRACK
DEVIATIONS TO THE WEST WOULD REQUIRE ADDITIONAL WARNINGS ALONG THE
NEW ENGLAND COAST.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      22/0900Z 33.0N  68.5W    90 KT
 12HR VT     22/1800Z 36.1N  68.7W    95 KT
 24HR VT     23/0600Z 40.1N  67.2W    90 KT
 36HR VT     23/1800Z 44.1N  63.1W    75 KT
 48HR VT     24/0600Z 48.0N  55.6W    60 KT...INLAND
 72HR VT     25/0600Z 51.0N  31.5W    40 KT...EXTRATROPICAL
 96HR VT     26/0600Z 54.0N  14.0W    30 KT...EXTRATROPICAL
120HR VT     27/0600Z 58.0N   4.0W    20 KT...EXTRATROPICAL
 
$$
FORECASTER BEVEN
 
NNNN


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Page last modified: Thursday, 31-Dec-2009 12:09:05 UTC