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Hurricane IGOR


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HURRICANE IGOR DISCUSSION NUMBER  41
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL112010
500 AM AST SAT SEP 18 2010
 
DATA FROM THE HURRICANE HUNTER AIRCRAFT INDICATE THAT WHILE THE
CENTRAL PRESSURE OF IGOR HAD FALLEN TO 939 MB...THE WINDS AT FLIGHT
LEVEL WERE NOT EFFICIENTLY MIXING DOWN TO THE SURFACE.  THE INITIAL
INTENSITY IS HELD AT 95 KT BASED ON A BLEND OF THE 115 KT FLIGHT-
LEVEL WIND MAXIMUM AND A MAXIMUM WIND OF 77 KT FROM THE SFMR. THE
OUTFLOW IS WELL ESTABLISHED...PARTICULARLY TO THE NORTH OF THE
CENTER...AND THE ENVIRONMENTAL CONDITIONS APPEAR FAVORABLE FOR A
LITTLE MORE STRENGTHENING OVER THE NEXT DAY OR SO BEFORE THE SHEAR
INCREASES.  THE OFFICIAL FORECAST SHOWS A PEAK AT 105 KT IN 24
HOURS AND THEN A SLOW WEAKENING THROUGH 48 HOURS. REGARDLESS OF THE
DETAILS OF THE INTENSITY FORECAST...IGOR WILL BE A LARGE AND
DANGEROUS HURRICANE AS IT APPROACHES BERMUDA ON SUNDAY. WEAKENING
IS EXPECTED TO CONTINUE BEYOND 48 HOURS...AS IGOR MOVES OVER COOLER
WATERS AND THE SHEAR INCREASES FURTHER.  ONCE IGOR COMPLETES
EXTRATROPICAL TRANSITION...IT WILL BE A LARGE AND POWERFUL CYCLONE
OVER THE NORTH ATLANTIC.
 
AFTER A SHORT TERM WOBBLE TOWARD THE WEST-NORTHWEST...THE LONG-TERM
INITIAL MOTION ESTIMATE IS 310/11.  IGOR IS SITUATED SOUTH OF A
MID-LEVEL RIDGE EXTENDING ALONG 35N...AND THIS RIDGE IS FORECAST BY
ALL OF THE MODELS TO WEAKEN AS A SHORTWAVE TROUGH PROGRESSES EAST
OFF THE U.S. EAST COAST IN THE NEXT DAY OR SO.  IGOR WILL TURN
NORTHWARD INTO THE WEAKNESS ALONG 65W ON SUNDAY AND PASS VERY NEAR
BERMUDA BEFORE TURNING NORTHEASTWARD ON MONDAY AHEAD OF ANOTHER
SHORTWAVE TROUGH MOVING OFF THE COAST OF NORTH AMERICA.  THE GLOBAL
MODELS SHOW THE RIDGE NORTH OF IGOR REMAINING A LITTLE STRONGER
THAN PREVIOUSLY FORECAST...AND AS A RESULT MOST OF THE GUIDANCE HAS
SHIFTED A LITTLE TO THE LEFT AND SLOWER THROUGH 48 HOURS.  THE
OFFICIAL FORECAST HAS BEEN ADJUSTED IN THIS DIRECTION...BUT REMAINS
TO THE RIGHT OF MOST OF THE GUIDANCE AND A LITTLE FASTER THAN
THE CONSENSUS.  BEYOND 48 HOURS...THE NEW NHC FORECAST IS LARGELY
AN UPDATE OF THE PREVIOUS PACKAGE...AND SHOWS IGOR ACCELERATING
TOWARD THE NORTHEAST AS IT BECOMES EXTRATROPICAL.
 
IGOR HAS A VERY LARGE WIND FIELD...WITH A RADIUS OF MAXIMUM WINDS OF
AROUND 45 NAUTICAL MILES AND HURRICANE FORCE WINDS EXTENDING OUT UP
TO 90 NM FROM THE CENTER.  CONDITIONS WILL BEGIN TO DETERIORATE ON
BERMUDA BY TONIGHT...WELL IN ADVANCE OF THE CENTER.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      18/0900Z 25.1N  62.8W    95 KT
 12HR VT     18/1800Z 26.2N  64.1W   100 KT
 24HR VT     19/0600Z 27.8N  65.1W   105 KT
 36HR VT     19/1800Z 29.9N  65.3W   100 KT
 48HR VT     20/0600Z 32.2N  64.7W    95 KT
 72HR VT     21/0600Z 38.5N  58.5W    80 KT
 96HR VT     22/0600Z 47.5N  46.5W    65 KT...POST-TROP/EXTRATROP
120HR VT     23/0600Z 51.5N  39.5W    55 KT...POST-TROP/EXTRATROP
 
$$
FORECASTER BRENNAN
 
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