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| #110864 (Received by flhurricane at: 4:46 PM 14.Sep.2006) TCDAT3 TROPICAL STORM HELENE DISCUSSION NUMBER 10 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL082006 500 PM EDT THU SEP 14 2006 THE OVERALL CLOUD PATTERN ASSOCIATED WITH HELENE HAS NOT CHANGED MUCH SINCE THIS MORNING...AND THERE ARE NO DISTINCT CONVECTIVE BANDING FEATURES. HOWEVER...THERE IS A SMALL BURST OF CONVECTION THAT HAS RECENTLY DEVELOPED NEAR THE CENTER. SATELLITE INTENSITY ESTIMATES REMAIN UNCHANGED FROM THIS MORNING AND THE INITIAL INTENSITY WILL REMAIN 40 KT. A RATHER DISTINCT LOW-LEVEL CIRCULATION BECAME APPARENT IN VISIBLE IMAGERY LATE THIS MORNING WHICH WAS A LITTLE TO THE RIGHT OF THE PREVIOUS TRACK...AND THIS REQUIRED A SLIGHT ADJUSTMENT BOTH TO THE WORKING TRACK AND TO THE SHORT TERM FORECAST. HELENE HAS SLOWED DOWN DURING THE PAST 6 HOURS...BUT USING A LONGER TERM 12 HOUR AVERAGE YIELDS AN INITIAL MOTION ESTIMATE OF 285/14. HELENE IS MOVING WEST-NORTHWESTWARD SOUTH OF A MID-TO UPPER-LEVEL RIDGE. THE GLOBAL MODELS IN GENERAL DEVELOP A BREAK IN THE RIDGE IN A COUPLE DAYS BETWEEN 50W AND 60W...WHICH SHOULD IMPART A MORE NORTHWESTWARD MOTION. HOWEVER...THERE REMAINS A FAIRLY LARGE SPREAD IN THE MODELS AS TO WHEN THIS MAY OCCUR. THE GFS...ITS ENSEMBLE MEAN...AND THE GFDL ARE TO THE RIGHT AND FORECAST THE RIDGE TO WEAKEN MUCH SOONER. THE UKMET KEEPS THE RIDGE INTACT LONGER AND THEREFORE IS ON THE LEFT SIDE OF THE GUIDANCE. THE OFFICIAL TRACK IS CLOSE TO THE FSU SUPERENSEMBLE AND GUNA MODEL CONSENSUS. EVEN THOUGH THE OUTFLOW IS WELL ESTABLISHED AND HELENE IS IN A VERY LOW SHEAR ENVIRONMENT...THE LARGE CIRCULATION STILL LACKS INNER CORE CONVECTION. UNTIL THE INNER CORE DEVELOPS...STRENGTHENING IS EXPECTED TO BE SLOW. THE NHC INTENSITY FORECAST SHOWS AN INCREASE IN WIND SPEED MUCH LIKE THE SHIPS MODEL. LATE IN THE PERIOD GLOBAL MODELS SUGGEST SOME INCREASING SHEAR WHICH COULD SLOW THE INTENSIFICATION. ACCORDINGLY...THE OFFICIAL FORECAST IS NOT AS AGGRESSIVE AS THE FSU SUPERENSEMBLE AT DAYS 4 AND 5. THE WIND RADII WERE ADJUSTED OUTWARD BASED ON A RECENT REPORT OF 34 KT WINDS FROM A MOORED BUOY ABOUT 90 NM NORTHWEST OF HELENE. FORECAST POSITIONS AND MAX WINDS INITIAL 14/2100Z 14.2N 37.6W 40 KT 12HR VT 15/0600Z 14.8N 39.7W 45 KT 24HR VT 15/1800Z 16.0N 42.1W 55 KT 36HR VT 16/0600Z 17.3N 44.4W 65 KT 48HR VT 16/1800Z 18.5N 46.2W 75 KT 72HR VT 17/1800Z 20.5N 49.0W 85 KT 96HR VT 18/1800Z 22.5N 51.0W 90 KT 120HR VT 19/1800Z 25.5N 54.0W 90 KT $$ FORECASTER BROWN |
