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Hurricane IGOR (Text)

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HURRICANE IGOR DISCUSSION NUMBER  22
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL112010
1100 AM AST MON SEP 13 2010
 
IGOR CONTINUES TO HAVE A DISTINCT EYE SURROUNDED BY TOPS OF -60C TO
-70C.  DVORAK CLASSIFICATIONS FROM TAFB AND SAB WERE 6.5...AND THE
INITIAL INTENSITY REMAINS 130 KT.  THE UW-CIMSS SECONDARY EYEWALL
FORMATION INDEX STRONGLY SUGGESTS THAT A SECONDARY EYEWALL WILL
FORM IN THE NEXT DAY OR TWO...AND THIS WILL LIKELY RESULT IN SOME
SHORT TERM INTENSITY FLUCTUATIONS THAT ARE NOT REPRESENTED IN THE
OFFICIAL FORECAST.  ON LONGER TIME SCALES...ALL OF THE INTENSITY
GUIDANCE SUGGESTS THAT IGOR IS NEAR PEAK INTENSITY...AND SHOW
GRADUAL WEAKENING THROUGH THE PERIOD.  HOWEVER...SINCE THE CYCLONE
REMAINS IN WHAT APPEARS TO BE AN IDEAL ENVIRONMENT FOR THE NEXT 72
HOURS...THE OFFICIAL FORECAST IS ADJUSTED ONLY SLIGHTLY DOWNWARD
THROUGH THAT TIME.  AT DAYS 4 AND 5...VERTICAL SHEAR MAY BEGIN TO
INCREASE OVER THE HURRICANE...HOWEVER...THIS INCREASE WILL BE
SENSITIVE TO THE VERY UNCERTAIN TRACK FORECAST AT THOSE TIME
RANGES.  THEREFORE...AT THOSE TIMES THE OFFICIAL FORECAST IS CLOSE
TO OR A LITTLE ABOVE THE STRONGEST MODEL...THE SHIPS.
 
THE INITIAL MOTION ESTIMATE IS 265/9 KNOTS...A LITTLE SLOWER THAN
BEFORE...AND A BIT SOUTH OF THE PREVIOUS FORECAST.  MOST OF THE
GUIDANCE...WITH THE EXCEPTION OF THE UKMET...SHOWS IGOR TURNING
TOWARD THE WEST-NORTHWEST BY TONIGHT AND THEN TURNING NORTHWESTWARD
BY 48 HOURS AS IT MOVES INTO A LARGE BREAK IN THE SUBTROPICAL
RIDGE. THE OFFICIAL FORECAST IS A LITTLE SOUTH OF THE PREVIOUS ONE
THROUGH 12 HOURS GIVEN THE INITIAL POSITION AND MOTION. FROM 12
THROUGH 48 HOURS THE OFFICIAL FORECAST IS SIMILAR TO BUT A LITTLE
SLOWER THAN THE PREVIOUS PACKAGE AND TRENDS TOWARD THE TVCN
CONSENSUS MODEL FORWARD SPEED. AT 72 HOURS AND BEYOND THERE IS
CONSIDERABLE UNCERTAINTY WITH THE EVOLUTION OF THE LARGE-SCALE FLOW
AND THE TRACK OF IGOR.  THE ECMWF AND UKMET SHOW MORE MID-LEVEL
RIDGING NORTH AND NORTHEAST OF IGOR OVER THE CENTRAL ATLANTIC AND
MOVE IGOR SLOWER AND FARTHER SOUTH THAN THE REST OF THE GUIDANCE AT
DAYS 3 THROUGH 5. THE GFS...GFDL...AND GFDN KEEP THIS RIDGE FARTHER
EAST AND ALLOW IGOR TO GAIN MORE LATITUDE AND RECURVE AHEAD OF A
LONGWAVE TROUGH SITUATED OFFSHORE OF THE NORTHEASTERN UNITED
STATES.  THE NOGAPS AND HWRF ARE BETWEEN THESE TWO CAMPS AND SHOW A
NORTHWESTWARD MOTION AT DAY 5. GIVEN THE INCREASING SPREAD OF THE
GUIDANCE LATE IN THE PERIOD...THE OFFICIAL FORECAST IS SIMPLY AN
UPDATE OF THE PREVIOUS ADVISORY AT THESE TIMES AND IS OF LOWER
CONFIDENCE THAN NORMAL. THE NHC TRACK IS CLOSE TO THE NOGAPS AND
WELL TO THE NORTH OF THE UKMET AND ECMWF AT THE END OF THE PERIOD.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      13/1500Z 17.5N  49.7W   130 KT
 12HR VT     14/0000Z 17.9N  50.8W   135 KT
 24HR VT     14/1200Z 18.7N  52.3W   130 KT
 36HR VT     15/0000Z 19.5N  53.7W   130 KT
 48HR VT     15/1200Z 20.6N  55.2W   125 KT
 72HR VT     16/1200Z 23.0N  58.0W   115 KT
 96HR VT     17/1200Z 25.5N  60.5W   110 KT
120HR VT     18/1200Z 29.0N  63.5W   100 KT
 
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FORECASTER BRENNAN
 
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