000WTNT41 KNHC 111449TCDAT1TROPICAL STORM IGOR DISCUSSION NUMBER 13NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL1120101100 AM AST SAT SEP 11 2010ALTHOUGH THE CONVECTIVE CLOUD TOPS HAVE WARMED...VISIBLE SATELLITEIMAGES SHOW A BANDING EYE PRESENTATION WITH IGOR. WHILE THEWEAKENING OF THE CONVECTION HAS LED TO A DECREASE IN DVORAKT-NUMBERS...IT IS PREMATURE TO LOWER THE INTENSITY AND 60 KT WILL BEKEPT FOR THIS ADVISORY. ALTHOUGH EASTERLY SHEAR REMAINS PRESENT...IT HAS DECREASED SINCEYESTERDAY AND IS FORECAST TO FURTHER DIMINISH DURING THE NEXT DAYOR SO. AROUND THAT TIME...THE CYCLONE IS FORECAST TO MOVE OVER WATERS WARMER THAN 28C. THESE CONDITIONS SHOULD PROMOTE GRADUALSTRENGTHENING IN THE SHORT-TERM...WITH THE POTENTIAL FOR A MORESIGNIFICANT INTENSIFICATION IN A COUPLE OF DAYS. INTERESTINGLY...WHILE THE STATISTICAL MODELS MAKE IGOR A CATEGORY 4 HURRICANE...THEGFDL AND HWRF MODELS SHOW SOME WEAKENING WITH IGOR BEFORERESTRENGTHENING THE CYCLONE IN A FEW DAYS. AT THIS POINT...I AMINCLINED TO LEAN ON THE STATISTICAL MODELS AT THE END OF THEPERIOD GIVEN THE FORECAST UPPER-LEVEL WIND PATTERN...AND HAVE RAISEDTHE WINDS FOR THAT TIME. MICROWAVE AND VISIBLE IMAGES SUGGEST THE SYSTEM HAS SLOWED A BIT ANDIS MOVING 275/17. THE GLOBAL MODELS ARE IN GOOD AGREEMENT ON AWESTWARD TRACK OF IGOR FOR THE NEXT FEW DAYS AS RIDGING REMAINSENTRENCHED TO THE NORTH. IN ABOUT 3 DAYS...THE WESTERN PART OF THERIDGE WEAKENS DUE TO A LARGE MID-LATITUDE TROUGH. THIS PATTERNSHOULD ALLOW IGOR TO GAIN A BIT MORE LATITUDE AND SLOW DOWN. WHILETHE MODELS ARE IN GENERAL AGREEMENT WITH THIS SCENARIO...THERE ARESOME LARGE SPEED DIFFERENCES...AS THE ECMWF IS SIGNIFICANTLY SLOWERTHAN MOST OF THE OTHER GUIDANCE. THE NHC FORECAST IS CLOSE TO THEPREVIOUS ONE...ON THE SOUTHERN AND WESTERN SIDES OF THE GUIDANCEENVELOPE...ATTEMPTING TO ACCOUNT FOR THE MODEL TENDENCIES OF BEINGTOO SLOW AND POLEWARD WITH LOW-LATITUDE SYSTEMS. FORECAST POSITIONS AND MAX WINDSINITIAL 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 KT120HR VT 16/1200Z 21.0N 59.5W 110 KT$$FORECASTER BLAKE
000WTNT41 KNHC 121823TCDAT1HURRICANE IGOR SPECIAL DISCUSSION NUMBER 18NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL112010130 PM AST SUN SEP 12 2010SATELLITE IMAGERY AND THE UW-CIMSS ADVANCED DVORAK TECHNIQUEINDICATE THAT IGOR HAS CONTINUED TO RAPIDLY INTENSIFY AND IS NOW ACATEGORY FOUR HURRICANE. THE VISIBLE AND BD-CURVE INFRARED ENHANCEMENT PICTURES REVEAL A CLEAR 20 NMI DIAMETER EYE WITH ASURROUNDING INTENSE INNER CORE RING OF -80 DEGREE CELSIUS CLOUD TOPTEMPERATURES. THE OFFICIAL INTENSITY FORECAST HAS BEEN MODIFIED TOINDICATE SOME ADDITIONAL INTENSIFICATION DURING THE NEXT 3 DAYS ANDTHEN SHOWS A SLIGHT DECREASE AT DAYS 4 AND 5. ALSO...FLUCTUATIONSIN STRENGTH DUE TO EYEWALL REPLACEMENT CYCLES ARE POSSIBLE...BUTTHERE IS LITTLE SKILL IN FORECASTING THE TIMING OF THESE CYCLES. THE WIND RADII FORECAST HAS ALSO BEEN ADJUSTED TO ACCOUNT FOR THEINCREASE IN THE INTENSITY. THE OFFICIAL NHC TRACK FORECAST REMAINSUNCHANGED FROM THE PREVIOUS ADVISORY. FORECAST POSITIONS AND MAX WINDSINITIAL 12/1830Z 17.7N 46.1W 115 KT 12HR VT 13/0000Z 17.8N 47.5W 125 KT 24HR VT 13/1200Z 18.0N 49.8W 125 KT 36HR VT 14/0000Z 18.4N 51.8W 125 KT 48HR VT 14/1200Z 19.0N 53.6W 130 KT 72HR VT 15/1200Z 20.7N 56.7W 130 KT 96HR VT 16/1200Z 22.6N 59.6W 125 KT120HR VT 17/1200Z 24.5N 62.5W 125 KT$$FORECASTER ROBERTS/BRENNAN