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| #375786 (Received by flhurricane at: 10:52 AM 13.Sep.2010) TCDAT1 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 $$ FORECASTER BRENNAN |
