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| #112350 (Received by flhurricane at: 4:55 AM 22.Sep.2006) TCDAT3 HURRICANE HELENE DISCUSSION NUMBER 40 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL082006 500 AM EDT FRI SEP 22 2006 THE INFRARED SATELLITE PRESENTATION OF HELENE HAS CHANGED LITTLE DURING THE PAST 6 HOURS WITH THE EYE REMAINING CLOUD-OBSCURED. A 22/0518Z AQUA-1 OVERPASS INDICATED HELENE HAD RETAINED GOOD LOW-LEVEL STRUCTURE...ALTHOUGH THE MID-LEVEL HAD ERODED OVER THE SOUTHERN SEMICIRCLE. SATELLITE CURRENT INTENSITY ESTIMATES REMAIN AT T4.5/77 KT...SO THE INITIAL INTENSITY REMAINS AT 75 KT. THE INITIAL MOTION ESTIMATE IS 040/13. HELENE IS MOVING NORTHEASTWARD AROUND THE WESTERN PERIPHERY OF A LARGE SUBTROPICAL RIDGE AS A DEEP-LAYER MID-LATITUDE TROUGH ALONG 65W LONGITUDE CONTINUES TO MOVE EASTWARD TOWARD THE CYCLONE. HELENE SHOULD BEGIN TO ACCELERATE AT A MORE RAPID PACE WITHIN THE NEXT 12 HOURS AS THE HURRICANE BECOMES EMBEDDED IN THE INCREASING SOUTHWESTERLY FLOW AHEAD OF THE APPROACHING TROUGH LOCATED TO THE WEST. BY 48 HOURS... HELENE IS EXPECTED TO PHASE UP WITH THE AFOREMENTIONED TROUGH AND BECOME A POWERFUL EXTRATROPICAL LOW PRESSURE SYSTEM TO THE NORTH OF THE AZORES ISLANDS. THE OFFICIAL FORECAST TRACK IS JUST AN UPDATE OF THE PREVIOUS TRACK...AND REMAINS NORTH OF THE MODEL CONSENSUS AND SIMILAR TO THE NOGAPS MODEL...WHICH PERFORMED WELL WITH GORDON. INCREASING VERTICAL SHEAR AND DECREASING SSTS WILL LIMIT ANY INTENSIFICATION TO THE NEXT 12 HOURS OR SO...BEFORE SLOW WEAKENING BEGINS AFTER THAT. HOWEVER...HELENE WILL BE PHASING UP WITH A STRONG NEGATIVELY-TILTED MID-LATITUDE TROUGH IN 36-48 HOURS...WHICH SHOULD HELP THE SYSTEM EVOLVE INTO A STRONG EXTRATROPICAL LOW. IT SHOULD BE NOTED THAT THE GFDL MODEL STRENGTHENS THE EXTRATROPICAL- HELENE CIRCULATION TO 108 KT BY 72 HOURS. WHILE THE INTENSIFICATION PROCESS IS LIKELY BEING OVERDONE BY THE MODEL OVERDONE...IT IS LIKELY A REASONABLE INDICATOR THAT HELENE WILL EVOLVE INTO A FORMIDABLE EXTRATROPICAL LOW...PROBABLY STRONGER THAN THE EXTRATROPICAL-GORDON CIRCULATION DID YESTERDAY. FORECAST POSITIONS AND MAX WINDS INITIAL 22/0900Z 32.9N 55.2W 75 KT 12HR VT 22/1800Z 35.0N 53.0W 75 KT 24HR VT 23/0600Z 37.6N 48.5W 70 KT 36HR VT 23/1800Z 40.3N 43.0W 65 KT...BECOMING EXTRATROPICAL 48HR VT 24/0600Z 43.0N 37.6W 60 KT...EXTRATROPICAL 72HR VT 25/0600Z 47.0N 30.0W 60 KT...EXTRATROPICAL 96HR VT 26/0600Z 51.5N 22.0W 60 KT...EXTRATROPICAL 120HR VT 27/0600Z 58.0N 15.0W 55 KT...EXTRATROPICAL $$ FORECASTER STEWART |
