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| #111253 (Received by flhurricane at: 4:52 PM 16.Sep.2006) TCDAT3 HURRICANE HELENE DISCUSSION NUMBER 18 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL082006 500 PM EDT SAT SEP 16 2006 DVORAK ESTIMATES FROM TAFB AND SAB HAVE NOT CHANGED AND A RAGGED EYE HAS BEEN OBSERVED THIS AFTERNOON IN THE VISIBLE IMAGERY. CIMSS EXPERIMENTAL ADVANCED DVORAK TECHNIQUE ALSO SUGGESTS MINIMAL HURRICANE INTENSITY. THUS...A 65 KT INITIAL INTENSITY IS RETAINED. TODAY...A NOAA SALEX...SAHARAN AIR LAYER EXPERIMENT...MISSION ON THE G-IV AIRCRAFT HAS BEEN TAKING OBSERVATIONS IN THE PERIPHERY OF HELENE. WHILE THESE DROPWINDSONDES ARE SHOWING SUBSTANTIAL DRY AIR...CIRA PRECIPITABLE WATER ANALYSES SUGGEST THAT SUFFICIENT MOISTURE IS FOUND IN THE SYSTEM'S INNER CORE. BECAUSE OF 27.5 C SSTS...LIGHT/MODERATE VERTICAL SHEAR...AND A MOIST ENVIRONMENT... CONTINUED SLOW INTENSIFICATION IS ANTICIPATED. AFTER TWO DAYS... BOTH THE SHEAR AND SSTS INCREASE. BECAUSE OF THESE CONFLICTING ENVIRONMENTAL FACTORS...HELENE IS PROJECTED TO PEAK IN INTENSITY NEAR 85 KT AT DAYS 2 AND 3 WITH SLIGHT WEAKENING THEREAFTER. IT IS NOTED THAT THE GFDL MODEL FIELDS RETAIN WEAKER SHEAR INTO LONGER LEAD TIMES THAN THE GLOBAL MODELS. THE OFFICIAL FORECAST IS SLIGHTLY ABOVE THE STANDARD SHIPS MODEL DUE TO THE INFLUENCE OF AN ENHANCING MICROWAVE PREDICTOR IN THE EXPERIMENTAL SHIPS-MICROWAVE MODEL AND IS SLIGHTLY BELOW THE PREVIOUS PREDICTION. CURRENT MOTION IS ESTIMATED TO BE 310/11. HELENE IS MOVING TOWARD A BREAK IN THE WEST-SOUTHWEST TO EAST-NORTHEAST ORIENTED SUBTROPICAL RIDGE AXIS. AFTER DAY 2...THERE IS A LARGE MODEL DIVERGENCE IN THE TRACK OF HELENE. THE GFDL AND UK QUICKLY ACCELERATE THE SYSTEM TO THE NORTH IN ADVANCE OF A STRONG SHORT WAVE MOVING OFF OF THE US ATLANTIC SEABOARD. IN CONTRAST...THE GFS...THE GFS ENSEMBLE AND THE ECMWF MODELS TURN HELENE TO THE WEST-NORTHWEST AND DO NOT HAVE IT PICKED UP BY THE SHORT WAVE TROUGH. THE NOGAPS AND GFDN MODELS...AS WELL AS CONSENSUS APPROACHES...SPLIT THE DIFFERENCE. AS IT IS DIFFICULT TO KNOW WHICH GROUP WILL BE CORRECT...THE TRACK FORECAST DEPICTED HERE IS CLOSE TO THE CONU CONSENSUS AND IS SLIGHTLY SLOWER AND JUST TO THE RIGHT OF THE PREVIOUS FORECAST. PERHAPS WITH THE MODEL ASSIMILATION OF THE SALEX DROPWINDSONDES... THE LARGE MODEL DIFFERENCES WILL BE REDUCED IN THE NEXT FORECAST CYCLE. FORECAST POSITIONS AND MAX WINDS INITIAL 16/2100Z 19.3N 46.3W 65 KT 12HR VT 17/0600Z 20.0N 47.4W 70 KT 24HR VT 17/1800Z 20.9N 48.7W 80 KT 36HR VT 18/0600Z 21.8N 49.8W 85 KT 48HR VT 18/1800Z 22.6N 51.0W 85 KT 72HR VT 19/1800Z 24.0N 53.5W 85 KT 96HR VT 20/1800Z 26.0N 56.0W 80 KT 120HR VT 21/1800Z 29.0N 57.5W 75 KT $$ FORECASTER BEVEN/LANDSEA |
