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| #375294 (Received by flhurricane at: 10:52 AM 11.Sep.2010) TCDAT1 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 |
