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Hurricane IGOR (Text)

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HURRICANE IGOR DISCUSSION NUMBER  27
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL112010
500 PM AST TUE SEP 14 2010
 
CLOUD TOPS SURROUNDING THE EYE HAVE COOLED CONSIDERABLY DURING THE
AFTERNOON AND THE EYE HAS ALSO WARMED AND BECOME MORE DISTINCT IN
BOTH VISIBLE AND INFRARED SATELLITE IMAGERY. SEVERAL DISTINCT
VORTICES INSIDE THE EYE WERE ALSO NOTED...SIMILAR TO WHAT HAS BEEN
SEEN WITH PAST HURRICANES THAT WERE NEAR CATEGORY 5 STRENGTH. THE
INITIAL INTENSITY IS INCREASED TO 125 KT AND IS SUPPORTED BY
SATELLITE INTENSITY ESTIMATES OF T6.5/127 KT FROM SAB...3-HR
AVERAGE ODT VALUES OF T6.7/133 KT FROM TAFB...AND UW-CIMSS ADT
VALUES OF T6.5/127 KT.

THE INITIAL MOTION ESTIMATE IS 295/07...BASED ON A 12-HR AVERAGE OF
SMOOTHING OUT THE MANY TROCHOIDAL WOBBLES IN THE TRACK. IGOR MAY
BRIEFLY WOBBLE BACK TO THE WEST DURING THE NEXT SEVERAL HOURS...BUT
THE GENERAL MOTION OVER THE NEXT 24 HOURS SHOULD BE TOWARD THE
WEST-NORTHWEST...FOLLOWED BY A TURN TO THE NORTHWEST AFTER THAT
THROUGH 72 HOURS. A SERIES OF SHORTWAVE TROUGHS MOVING QUICKLY IN
THE MID-LATITUDE WESTERLIES ACROSS THE NORTHERN U.S. AND THE NORTH
ATLANTIC IS FORECAST TO GRADUALLY WEAKEN THE SUBTROPICAL RIDGE
BETWEEN 60W-70W LONGITUDE ABOUT EVERY 24-36 HOURS. AS A RESULT...
IGOR IS EXPECTED TO TURN NORTHWARD IN 96-120 HOURS AS DEEP-LAYER
SOUTHERLY FLOW TO THE EAST OF IGOR STRENGTHENS BETWEEN IT AND A
STRONG SUBTROPICAL HIGH FORECAST OT BE NEAR 30N/40W BY THAT TIME.
THE OFFICIAL FORECAST TRACK IS SIMILAR TO THE PREVIOUS ADVISORY AND
IS CLOSE TO THE MIDDLE OF THE TIGHTLY CLUSTERED MODEL GUIDANCE. BY
120 HOURS...IGOR IS EXPECTED TO BE A VERY LARGE HURRICANE AND BE
CLOSE ENOUGH TO BERMUDA TO BRING ADVERSE WEATHER CONDITIONS TO THAT
ISLAND.

IGOR IS FORECAST TO REMAIN IN AN ENVIRONMENT OF LIGHT VERTICAL WIND
SHEAR...WARM SEA-SURFACE TEMPERATURES OF NEAR 29C...AND MAINTAIN A
VERY FAVORABLE OUTFLOW PATTERN THROUGH THE FORECAST PERIOD. AS A
RESULT...THERE MAY BE SOME ADDITIONAL STRENGTHENING DURING THE NEXT
12-24 HOURS...ESPECIALLY LATER TONIGHT DURING THE CONVECTIVE
MAXIMUM PERIOD. HOWEVER...OWING TO THE LARGE SIZE OF IGOR...ITS
STRONG CATEGORY 4 INTENSITY...AND ITS RELATIVELY SLOW FORWARD
MOTION OF LESS THAN 10 KT...SOME COLD UPWELLING MAY OCCUR BENEATH
THE CORE OF THE HURRICANE AND CAUSE SOME WEAKENING OF THE CYCLONE
DESPITE THE AFOREMENTIONED FAVORABLE CONDITIONS. EYEWALL
REPLACEMENT CYCLES ARE ALSO A DISTINCT POSSIBILITY. REGARDLESS...
IGOR IS STILL EXPECTED TO REMAIN A MAJOR HURRICANE THROUGH THE
FORECAST PERIOD. THE OFFICIAL INTENSITY FORECAST IS A LITTLE HIGHER
THAN THE PREVIOUS ADVISORY AND IS SIMILAR TO A BLEND OF THE
SHIPS-LGEM INTENSITY MODELS THROUGH 72 HOURS.  IT APPEARS AS THOUGH
THE SHIPS GUIDANCE AT FOUR AND FIVE DAYS MAY BE ADVERSELY AFFECTED
BY THE REPRESENTATION OF THE WARM CORE OF THE HURRICANE IN THE GFS
MODEL.  IN ADDITION...ALL THE GLOBAL MODELS FORECAST A VERY
FAVORABLE OUTFLOW PATTERN THROUGH DAY FIVE...AND SO THE OFFICIAL
FORECAST IS HELD A LITTLE ABOVE THE GUIDANCE NEAR THE END OF THE
FORECAST PERIOD.

FORECAST POSITIONS AND MAX WINDS
 
INITIAL      14/2100Z 18.8N  53.1W   125 KT
 12HR VT     15/0600Z 19.5N  54.3W   130 KT
 24HR VT     15/1800Z 20.5N  55.6W   125 KT
 36HR VT     16/0600Z 21.5N  57.2W   125 KT
 48HR VT     16/1800Z 22.6N  58.8W   120 KT
 72HR VT     17/1800Z 25.4N  62.1W   115 KT
 96HR VT     18/1800Z 28.6N  64.5W   110 KT
120HR VT     19/1800Z 33.0N  65.5W   100 KT
 
$$
FORECASTER STEWART
 
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