Hurricane IGOR

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HURRICANE IGOR DISCUSSION NUMBER  17
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL112010
1100 AM AST SUN SEP 12 2010
 
CONVENTIONAL AND MICROWAVE IMAGERY SHOWS THAT IGOR IS GOING THROUGH
A PERIOD OF RAPID INTENSIFICATION.  VISIBLE IMAGERY DEPICTS A
CLEARING EYE AND INFRARED IMAGERY AND AN SSMIS OVERPASS REVEAL AN
INTENSE FULLY-DEVELOPED INNER RING OF DEEP CONVECTION. THE OUTFLOW
HAS BECOME QUITE IMPRESSIVE...PARTICULARLY OVER THE EASTERN PORTION
OF THE CYCLONE WHERE THE COLDEST CLOUD TOPS RESIDE. THE INITIAL
INTENSITY OF 90 KT IS BASED ON A COMPROMISE OF SATELLITE INTENSITY
ESTIMATES OF 77 AND 90 KT FROM SAB AND TAFB...RESPECTIVELY...A
UW-CIMSS ADT OF 107 KT...AND A SATELLITE CONSENSUS OF 86 KT...THAT
INCLUDES A BLEND OF AMSU MICROWAVE ESTIMATES.  THE INTENSITY
FORECAST HAS BEEN ADJUSTED UPWARD FROM THE PREVIOUS FORECAST TO
ACCOUNT FOR THE RI TREND...AND INDICATES STRENGTHENING TO A MAJOR
HURRICANE IN 12 HOURS...WITH FURTHER INTENSIFICATION TO A CATEGORY
FOUR HURRICANE BY DAY 2.  THE FORECAST IS BASED ON THE ICON
CONSENSUS BUT IS HEDGED A BIT MORE TOWARD THE SHIPS AND LGEM BEYOND
48 HOURS.
 
THE INITIAL MOTION IS ESTIMATED TO BE 270/11...WITHIN THE DEEP-LAYER
EASTERLY FLOW OF THE SUBTROPICAL RIDGE NORTH OF IGOR. THE LARGE-
SCALE MODELS SUGGEST THAT A DEVELOPING WEAKNESS IN THE RIDGE
OVER THE WESTERN ATLANTIC WILL RESULT IN A WEST-NORTHWESTWARD TURN
IN ABOUT 36 HOURS.  AFTERWARD...A TURN TOWARD THE NORTHWEST IS
INDICATED AS IGOR ROUNDS THE SOUTHWESTERN PERIPHERY OF THE RIDGE
AND MOVES INTO THE WEAKNESS.  THERE IS CONSIDERABLE SPREAD IN THE
DYNAMICAL MODEL GUIDANCE BEYOND DAY 2.  A CLUSTER THAT INCLUDES THE
GFDL...THE GFS AND THE GEFS ENSEMBLE MEAN SUGGESTS A WEAKER RIDGE
AND AN EARLIER TURN TOWARD THE NORTHWEST.  THE OFFICIAL FORECAST IS
BASED ON PRIMARILY ON THE TVCN MULTI-MODEL CONSENSUS BUT IS
ADJUSTED SLIGHTLY TO THE LEFT OF THE PREVIOUS ADVISORY BEYOND DAY 3
AND CLOSER TO THE UKMET...ECMWF...AND THE ECMWF ENSEMBLE MEAN.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      12/1500Z 17.7N  45.7W    90 KT
 12HR VT     13/0000Z 17.8N  47.5W   105 KT
 24HR VT     13/1200Z 18.0N  49.8W   110 KT
 36HR VT     14/0000Z 18.4N  51.8W   115 KT
 48HR VT     14/1200Z 19.0N  53.6W   115 KT
 72HR VT     15/1200Z 20.7N  56.7W   125 KT
 96HR VT     16/1200Z 22.6N  59.6W   125 KT
120HR VT     17/1200Z 24.5N  62.5W   125 KT
 
$$
FORECASTER ROBERTS/BRENNAN
 
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