Tropical Storm IGOR

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TROPICAL STORM IGOR DISCUSSION NUMBER  13
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL112010
1100 AM AST SAT SEP 11 2010
 
ALTHOUGH THE CONVECTIVE CLOUD TOPS HAVE WARMED...VISIBLE SATELLITE
IMAGES SHOW A BANDING EYE PRESENTATION WITH IGOR.  WHILE THE
WEAKENING OF THE CONVECTION HAS LED TO A DECREASE IN DVORAK
T-NUMBERS...IT IS PREMATURE TO LOWER THE INTENSITY AND 60 KT WILL BE
KEPT FOR THIS ADVISORY.  

ALTHOUGH EASTERLY SHEAR REMAINS PRESENT...IT HAS DECREASED SINCE
YESTERDAY AND IS FORECAST TO FURTHER DIMINISH DURING THE NEXT DAY
OR SO.  AROUND THAT TIME...THE CYCLONE IS FORECAST TO MOVE OVER 
WATERS WARMER THAN 28C.  THESE CONDITIONS SHOULD PROMOTE GRADUAL
STRENGTHENING IN THE SHORT-TERM...WITH THE POTENTIAL FOR A MORE
SIGNIFICANT INTENSIFICATION IN A COUPLE OF DAYS.  INTERESTINGLY...
WHILE THE STATISTICAL MODELS MAKE IGOR A CATEGORY 4 HURRICANE...THE
GFDL AND HWRF MODELS SHOW SOME WEAKENING WITH IGOR BEFORE
RESTRENGTHENING THE CYCLONE IN A FEW DAYS.  AT THIS POINT...I AM
INCLINED TO LEAN ON THE STATISTICAL MODELS AT THE END OF THE
PERIOD GIVEN THE FORECAST UPPER-LEVEL WIND PATTERN...AND HAVE RAISED
THE WINDS FOR THAT TIME.  

MICROWAVE AND VISIBLE IMAGES SUGGEST THE SYSTEM HAS SLOWED A BIT AND
IS MOVING 275/17.  THE GLOBAL MODELS ARE IN GOOD AGREEMENT ON A
WESTWARD TRACK OF IGOR FOR THE NEXT FEW DAYS AS RIDGING REMAINS
ENTRENCHED TO THE NORTH.  IN ABOUT 3 DAYS...THE WESTERN PART OF THE
RIDGE WEAKENS DUE TO A LARGE MID-LATITUDE TROUGH.  THIS PATTERN
SHOULD ALLOW IGOR TO GAIN A BIT MORE LATITUDE AND SLOW DOWN.  WHILE
THE MODELS ARE IN GENERAL AGREEMENT WITH THIS SCENARIO...THERE ARE
SOME LARGE SPEED DIFFERENCES...AS THE ECMWF IS SIGNIFICANTLY SLOWER
THAN MOST OF THE OTHER GUIDANCE.  THE NHC FORECAST IS CLOSE TO THE
PREVIOUS ONE...ON THE SOUTHERN AND WESTERN SIDES OF THE GUIDANCE
ENVELOPE...ATTEMPTING TO ACCOUNT FOR THE MODEL TENDENCIES OF BEING
TOO SLOW AND POLEWARD WITH LOW-LATITUDE SYSTEMS.  

FORECAST POSITIONS AND MAX WINDS
 
INITIAL      11/1500Z 17.4N  39.5W    60 KT
 12HR VT     12/0000Z 17.5N  42.0W    65 KT
 24HR VT     12/1200Z 17.6N  44.9W    70 KT
 36HR VT     13/0000Z 17.7N  47.5W    80 KT
 48HR VT     13/1200Z 17.7N  49.7W    90 KT
 72HR VT     14/1200Z 18.0N  53.5W   105 KT
 96HR VT     15/1200Z 19.5N  56.5W   110 KT
120HR VT     16/1200Z 21.0N  59.5W   110 KT
 
$$
FORECASTER BLAKE
 
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