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| #110821 (Received by flhurricane at: 10:49 AM 14.Sep.2006) TCDAT3 TROPICAL STORM HELENE DISCUSSION NUMBER 9 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL082006 1100 AM EDT THU SEP 14 2006 A QUIKSCAT AMBIGUITY ANALYSIS FROM 0802 UTC WAS HELPFUL IN LOCATING THE CENTER WHICH WAS FURTHER SOUTH THAN THE PREVIOUS ADVISORY. VISIBLE SATELLITE IMAGERY SUGGESTS HELENE IS SLOWLY BECOMING BETTER ORGANIZED WITH INCREASING CURVATURE NOTED IN THE BANDING FEATURES. SATELLITE INTENSITY ESTIMATES ARE 45 KT FROM TAFB...35 KT FROM SAB AND AFWA. THE INITIAL INTENSITY IS INCREASED SLIGHTLY TO 40 KT FOR THIS ADVISORY. THE STORM CONTINUES TO RACE WESTWARD AT 275/20 AS IT CURRENTLY REMAINS SOUTH OF THE SUBTROPICAL RIDGE. THE SPREAD IN THE TRACK GUIDANCE REMAINS LARGE ESPECIALLY BEYOND 24 TO 36 HOURS. AS NOTED IN THE PREVIOUS DISCUSSION...THE MODELS OFFER TWO SOLUTIONS. THE GFS...ITS ENSEMBLE MEAN...AND THE GFDL ARE TO THE RIGHT AND FORECAST THE RIDGE TO THE NORTH TO WEAKEN QUITE RAPIDLY ALLOWING THE STORM TO TURN NORTHWESTWARD IN ABOUT 12 HOURS. THE UKMET KEEPS THE SUBTROPICAL RIDGE AND MAINTAINS A WEST-NORTHWEST TRACK LONGER. IN GENERAL ALL OF THE MODELS DECREASE THE FORWARD SPEED BY HALF OVER THE CENTRAL ATLANTIC DURING DAYS 3-5. BY THAT TIME THE TRACK FORECAST IS QUITE UNCERTAIN SINCE THE GUIDANCE ENVELOPE IS MORE THAN 450 MILES WIDE. THE NEW OFFICIAL TRACK FORECAST IS MOVED TO THE LEFT OF THE PREVIOUS ADVISORY...AND NOW IN AGREEMENT WITH THE MODEL CONSENSUS. THE INTENSIFICATION OF HELENE IS LIKELY TO BE SLOW INITIALLY BECAUSE OF THE CURRENTLY BROAD CIRCULATION OF THE CYCLONE. CONVECTION SHOULD EVENTUALLY CONSOLIDATE NEAR THE CIRCULATION CENTER AND ALLOW FOR MORE STEADY STRENGTHENING DURING THE NEXT DAY OR TWO. SSTS ALONG THE FORECAST TRACK ARE FORECAST TO REMAIN 27-28 CELSIUS AND THE SYSTEM IS EXPECTED TO REMAIN IN A WEAK SHEAR ENVIRONMENT. THUS HELENE IS FORECAST TO BECOME A HURRICANE BY 36 HOURS. THE SHIPS AND GFDL MODELS INDICATE A PEAK INTENSITY OF 90-95 KT WHILE THE FSU SUPERENSEMBLE INDICATES HELENE COULD BECOME A MAJOR HURRICANE. THE OFFICIAL FORECAST IS LOWER THAN ALL THE GUIDANCE FOR THE FIRST DAY OR TWO GIVEN THE CURRENT SLOW RATE OF INTENSIFICATION THEREAFTER...THE FORECAST IS CLOSE TO THE SHIPS AND GFDL GUIDANCE AND BRINGS HELENE TO A CATEGORY TWO HURRICANE. FORECAST POSITIONS AND MAX WINDS INITIAL 14/1500Z 13.4N 36.8W 40 KT 12HR VT 15/0000Z 13.8N 39.1W 45 KT 24HR VT 15/1200Z 14.8N 42.0W 55 KT 36HR VT 16/0000Z 16.2N 44.1W 65 KT 48HR VT 16/1200Z 17.5N 46.0W 75 KT 72HR VT 17/1200Z 19.5N 49.0W 85 KT 96HR VT 18/1200Z 21.5N 51.0W 90 KT 120HR VT 19/1200Z 24.5N 53.0W 90 KT $$ FORECASTER COBB/BEVEN |
