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Hurricane IGOR


ZCZC MIATCDAT1 ALL
TTAA00 KNHC DDHHMM
HURRICANE IGOR DISCUSSION NUMBER  43
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL112010
500 PM AST SAT SEP 18 2010

IGOR CONTINUES WORKING ITS WAY THROUGH AN EYEWALL REPLACEMENT CYCLE. 
AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT INVESTIGATING IGOR
FOUND A FRAGMENT OF THE INNER EYEWALL REMAINING INSIDE AN 85 N MI
WIDE OUTER EYEWALL.  THE CENTRAL PRESSURE WAS 945 MB.  THE MAXIMUM
700-MB FLIGHT-LEVEL WINDS WERE 113 KT...WHILE THE MAXIMUM ESTIMATED
SURFACE WINDS FROM THE SFMR WERE 73 KT.  SURFACE WIND ESTIMATES
FROM TWO EYEWALL DROPSONDES WERE NEAR 70 KT AND CONSISTENT WITH THE
COINCIDENT SFMR READINGS.  BASED ON THESE DATA...THE INITIAL
INTENSITY IS REDUCED TO 85 KT...AND IT IS POSSIBLE THAT THIS IS A
LITTLE GENEROUS.
 
THE INITIAL MOTION IS 320/12.  THERE IS NO CHANGE TO THE FORECAST
PHILOSOPHY...AND ONLY MINOR TWEAKS TO THE FORECAST TRACK FROM THE
PREVIOUS ADVISORY.  DURING THE NEXT 36-72 HR...IGOR WILL ROUND THE
WESTERN END OF A DEEP-LAYER RIDGE OVER THE CENTRAL AND EASTERN
ATLANTIC AND ENTER THE WESTERLIES TO THE EAST OF A SHORTWAVE TROUGH
MOVING OFF THE COAST OF EASTERN NORTH AMERICA.  THE TRACK GUIDANCE
REMAINS IN GOOD AGREEMENT WITH THIS SCENARIO...WITH THE CENTER OF
IGOR PASSING NEAR OR OVER BERMUDA IN ABOUT 36 HR.  AFTER 72 HR...
THERE REMAINS SPREAD IN THE GUIDANCE AS IGOR UNDERGOES
EXTRATROPICAL TRANSITION.  THIS PART OF THE TRACK IS SHIFTED A
LITTLE TO THE EAST OF THE PREVIOUS FORECAST BASED ON A BLEND OF THE
DYNAMICAL MODELS...AND IT NOW LIES NEAR THE MIDDLE OF THE GUIDANCE
ENVELOPE.

IT APPEARS UNLIKELY THAT IGOR WILL COMPLETE THE EYEWALL REPLACEMENT
CYCLE IN TIME TO SIGNIFICANTLY STRENGTHEN GIVEN THE CURRENT
INTERNAL TRENDS AND THE EXPECTATION OF INCREASED VERTICAL WIND
SHEAR AFTER 24 HR.  NONE OF THE GUIDANCE SHOWS SIGNIFICANT
STRENGTHENING...AND THE NEW INTENSITY FORECAST NOW CALLS FOR LITTLE
CHANGE IN STRENGTH DURING THE NEXT 36 HR.  AFTER THAT...IGOR SHOULD
WEAKEN DUE TO INCREASING SHEAR.  EXTRATROPICAL TRANSITION SHOULD BE
UNDERWAY BY 72 HR AND BE COMPLETE BY 96 HR.  IGOR IS EXPECTED TO
REMAIN A LARGE AND POWERFUL CYCLONE AFTER EXTRATROPICAL
TRANSITION...AND THIS IS REFLECTED IN THE 96-120 HR INTENSITY
FORECAST.
 
IGOR CONTINUES TO HAVE A VERY LARGE WIND FIELD...AND CONDITIONS WILL
BEGIN TO DETERIORATE ON BERMUDA TONIGHT WELL IN ADVANCE OF THE
CENTER.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      18/2100Z 27.1N  64.3W    85 KT
 12HR VT     19/0600Z 28.4N  65.0W    85 KT
 24HR VT     19/1800Z 30.5N  65.4W    85 KT
 36HR VT     20/0600Z 33.1N  64.9W    85 KT
 48HR VT     20/1800Z 36.1N  62.6W    80 KT
 72HR VT     21/1800Z 42.5N  52.5W    75 KT
 96HR VT     22/1800Z 48.0N  42.0W    75 KT...POST-TROP/EXTRATROP
120HR VT     23/1800Z 50.0N  35.0W    60 KT...POST-TROP/EXTRATROP
 
$$
FORECASTER BEVEN
 
NNNN


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Page last modified: Friday, 15-Apr-2011 12:09:14 UTC