Hurricane IGOR

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HURRICANE IGOR DISCUSSION NUMBER  23
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL112010
500 PM AST MON SEP 13 2010
 
THE STRUCTURE OF IGOR HAS CHANGED LITTLE OVER THE PAST FEW HOURS.
THE EYE REMAINS VERY DISTINCT IN IR AND VISIBLE IMAGERY...AND
ALTHOUGH THE TOPS SURROUNDING THE EYE HAVE WARMED A BIT...DVORAK
CLASSIFICATIONS STILL SUPPORT AN INTENSITY OF 130 KT.  IGOR WILL
REMAIN IN A FAVORABLE ENVIRONMENT FOR MAINTAINING ITS CURRENT
INTENSITY FOR THE NEXT COUPLE OF DAYS...AND THE OFFICIAL FORECAST
DOES NOT SHOW ANY WEAKENING UNTIL AFTER 48 HOURS.  WHILE A 1640 UTC
AMSR-E PASS DOES NOT SHOW ANY EVIDENCE OF A SECONDARY EYEWALL
YET...IT IS POSSIBLE THAT AN EYEWALL REPLACEMENT CYCLE WILL OCCUR
IN THE FIRST COUPLE OF DAYS...WHICH COULD RESULT IN SOME INTENSITY
FLUCTUATIONS NOT REPRESENTED IN THE OFFICIAL FORECAST.  BEYOND 36
HOURS...ALL OF THE INTENSITY GUIDANCE SUGGEST THAT SLOW WEAKENING
SHOULD BEGIN...ALTHOUGH THERE ARE NO OVERLY NEGATIVE FACTORS UNTIL
THE VERY END OF THE PERIOD WHEN THE VERTICAL SHEAR MAY INCREASE.
THE OFFICIAL FORECAST SHOWS A GRADUAL WEAKENING AT DAYS 3 THROUGH 5
BUT IS HIGHER THAN MOST OF THE GUIDANCE THROUGH THE PERIOD.
 
THE INITIAL MOTION IS STILL DUE WEST...270 DEGREES...AT 9 KNOTS.
ALL OF THE GUIDANCE...EXCEPT THE UKMET...INSISTS ON A TURN TOWARD
THE WEST-NORTHWEST IN THE NEXT 12 HOURS AS IGOR BEGINS TO MOVE INTO
A LARGE WEAKNESS IN THE SUBTROPICAL RIDGE.  HOWEVER...DUE TO THE
INITIAL POSITION AND MOTION...THE OFFICIAL FORECAST HAS AGAIN BEEN
ADJUSTED A LITTLE TO THE LEFT OF THE PREVIOUS ADVISORY THROUGH 48
HOURS.  BEYOND THAT TIME...THERE IS STILL SOME SPREAD IN THE TRACK
GUIDANCE.  THE ECMWF AND UKMET STILL SHOW A STRONGER RIDGE NORTH OF
IGOR THROUGH MUCH OF THE PERIOD...TAKING THE CYCLONE FARTHER WEST
THAN THE REST OF THE GUIDANCE.  THE GFS AND GFDL CONTINUE TO SHOW
THE LEAST RIDGING AND TURN IGOR NORTH-NORTHWESTWARD AT THE END OF
THE PERIOD AHEAD OF A MID-LATITUDE TROUGH.  WHILE CONFIDENCE IN THE
TRACK FORECAST LATE IN THE PERIOD REMAINS LOW...THE GUIDANCE SHOWS
A LITTLE LESS SPREAD NOW THAN EARLIER TODAY.  THE NEW OFFICIAL
FORECAST SHOWS A NORTHWESTWARD MOTION AT DAYS 3 THROUGH 5...AND IS
SIMILAR TO THE PREVIOUS FORECAST.  THIS ENDS UP BEING VERY CLOSE TO
THE TVCN MULTI-MODEL CONSENSUS AND A BLEND OF THE GFS AND ECMWF
MODELS.

LARGE SWELLS FROM IGOR WILL BEGIN AFFECTING THE LEEWARD ISLANDS
TOMORROW AND REACH PUERTO RICO AND THE VIRGIN ISLANDS BY WEDNESDAY.  
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      13/2100Z 17.7N  50.5W   130 KT
 12HR VT     14/0600Z 18.1N  51.7W   130 KT
 24HR VT     14/1800Z 18.9N  53.2W   130 KT
 36HR VT     15/0600Z 20.0N  54.7W   130 KT
 48HR VT     15/1800Z 21.1N  56.1W   130 KT
 72HR VT     16/1800Z 23.5N  58.5W   120 KT
 96HR VT     17/1800Z 26.5N  61.5W   110 KT
120HR VT     18/1800Z 30.0N  64.0W   105 KT
 
$$
FORECASTER BRENNAN
 
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