Hurricane IGOR

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HURRICANE IGOR DISCUSSION NUMBER  20
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL112010
1100 PM AST SUN SEP 12 2010
 
IGOR HAS CONTINUED TO INTENSIFY WITH VERY COLD CLOUD TOPS...LOWER
THAN -70C...WRAPPING AROUND THE SLOWLY-SHRINKING EYE DURING THE
PAST SEVERAL HOURS.  ALTHOUGH THE TOPS HAVE RECENTLY WARMED A
LITTLE OVER THE SOUTHWEST QUADRANT...SUBJECTIVE DVORAK ESTIMATES
FROM TAFB AND SAB ARE T6.5/127 KT AND OBJECTIVE ESTIMATES FROM THE
ADT AND HIE ALGORITHMS ARE T6.6/130 KT AND T6.9/137 KT...
RESPECTIVELY.  AS A COMPROMISE...THE INITIAL INTENSITY IS SET AT
130 KT.  AN EXPERIMENTAL PRODUCT FROM UW-CIMSS RUN AT NHC INDICATES
THAT THERE IS A 42 PERCENT CHANCE OF SECONDARY EYEWALL FORMATION
WITHIN THE NEXT 12 HOURS...AND A 90 PERCENT CHANCE WITHIN 24 HOURS.
THE PERIOD OF RAPID INTENSIFICATION IS LIKELY TO END SOON...BUT THE
OFFICIAL FORECAST FOLLOWS THE SHIPS/LGEM MODELS BY SHOWING IGOR
REACHING THE THRESHOLD OF CATEGORY 5 STRENGTH BEFORE THAT HAPPENS.
SOME WEAKENING IS THEN INDICATED AFTER EYEWALL REPLACEMENT
OCCURS...BUT IGOR IS EXPECTED TO REMAIN A POWERFUL HURRICANE FOR
SEVERAL DAYS.  AS IS ALWAYS THE CASE WITH STRONG HURRICANES LIKE
IGOR...FLUCTUATIONS IN INTENSITY ARE LIKELY BUT ARE ALSO DIFFICULT
TO FORECAST.
 
THE MEAN MOTION IS 270/11...BUT IGOR HAS BEEN WOBBLING A LITTLE TO
THE SOUTH OF THAT VECTOR.  IGOR IS MOVING INTO AN ENVIRONMENT WHERE
THE STEERING FLOW IS BECOMING INCREASINGLY DICTATED BY A LARGE
LONGWAVE TROUGH OVER THE WESTERN ATLANTIC...AND THE HURRICANE IS
EXPECTED TO RESPOND BY TURNING TOWARD THE WEST-NORTHWEST WITHIN THE
NEXT 24-48 HOURS.  SOME OF THE GLOBAL MODELS INDICATE THAT THE
TROUGH COULD FLATTEN A LITTLE BY DAY 3 AND ALLOW THE SUBTROPICAL
RIDGE TO BUILD WESTWARD...BUT AT THIS TIME THERE IS TOO MUCH
DISAGREEMENT TO INDICATE A WESTWARD TURN IN THE FORECAST.  THE
TRACK GUIDANCE HAS SHIFTED A LITTLE TO THE NORTH...BUT THE NEW
OFFICIAL FORECAST STILL LIES ON THE SOUTHERN SIDE OF THE GUIDANCE
ENVELOPE UNTIL IT BECOMES CLEAR THAT IGOR IS READY TO TURN.  THIS
SOLUTION ALSO GIVES CREDENCE TO THE MORE SOUTHERN ECMWF AND UKMET
MODELS.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      13/0300Z 17.6N  47.8W   130 KT
 12HR VT     13/1200Z 17.8N  49.5W   140 KT
 24HR VT     14/0000Z 18.2N  51.3W   135 KT
 36HR VT     14/1200Z 18.9N  53.0W   130 KT
 48HR VT     15/0000Z 19.8N  54.6W   125 KT
 72HR VT     16/0000Z 22.0N  57.5W   125 KT
 96HR VT     17/0000Z 24.0N  60.0W   120 KT
120HR VT     18/0000Z 27.0N  63.0W   110 KT
 
$$
FORECASTER BERG
 
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