Hurricane HELENE

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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
 
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