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| #112505 (Received by flhurricane at: 5:00 AM 23.Sep.2006) TCDAT3 TROPICAL STORM HELENE DISCUSSION NUMBER 44 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL082006 500 AM EDT SAT SEP 23 2006 A SMALL BURST OF CONVECTION WITH CLOUD TOPS TO -60C HAVE PERSISTED OVER THE LOW-LEVEL CENTER FOR MORE THAN 6 HOURS...INDICATING THAT HELENE STILL POSSESSES WARM-CORE TROPICAL CHARACTERISTICS. DVORAK SATELLITE CURRENT INTENSITY ESTIMATES ARE T3.5/55 KT FROM TAFB AND XT3.5/55 KT FROM AFWA. GIVEN THE FORWARD SPEED IS NOW 22 KT...THE ADDITIONAL TRANSLATIONAL SPEED EASILY SUPPORTS 60 KT FOR THE INTENSITY...ALTHOUGH THE INTENSITY COULD BE HIGHER. THE INITIAL MOTION IS 060/22. THERE IS NO SIGNIFICANT CHANGE TO THE PREVIOUS FORECAST TRACK OR REASONING. AFTER THE SLIGHT EASTWARD JOG ON THE PREVIOUS ADVISORY...HELENE APPEARS TO HAVE RETURNED TO A BASE COURSE OF 060 DEGREES...AND THAT GENERAL MOTION IS FORECAST TO CONTINUE THROUGHOUT THE PERIOD BASED ON THE GFDL...GFDN...NOGAPS... GFS...AND GFS ENSEMBLE MODELS. HOWEVER...THERE ARE SOME DISPARITIES BETWEEN THOSE MODELS AND THE UKMET AND ECMWF MODELS. BY 72 HOURS... THE LATTER TWO MODELS DROP A PIECE OF STRONG SHORTWAVE ENERGY INTO THE BASE OF THE LARGE-SCALE TROUGH THAT IS CAPTURING HELENE....AND DEVELOP A CLOSED LOW THAT DROPS SOUTHWARD OVER THE AZORES. THE OTHER MODELS DO THE SAME EXCEPT THAT THEY MERELY WEAKEN HELENE AND KEEP THE CYCLONE MOVING EAST-NORTHEASTWARD TOWARD THE BRITISH ISLES RATHER THAN RAPIDLY DEEPENING HELENE AND TAKING THE CYCLONE SOUTHWARD OVER THE AZORES. GIVEN THAT HELENE IS A DISTINCT ENTITY THAT IS STILL VERTICALLY DEEP...IT SEEMS UNLIKELY THAT THERE WILL BE ENOUGH TIME FOR A NEW MID-LEVEL LOW THAT IS FORECAST TO DEVELOP SOUTH OF HELENE TO CAPTURE THE CYCLONE AND FORCE IT SOUTHWARD IN 72-120 HOURS LIKE THE UKMET AND ECMWF MODELS ARE INDICATING. COLD AIR STRATOCUMULUS CLOUDS ARE POISED TO BE DRAWN INTO THE CENTER OF HELENE...AND EXTRATROPICAL TRANSITION IS POSSIBLE AS EARLY AS THE 12-H FORECAST PERIOD. BY 24 AND THROUGH 48 HOURS...A SHOT OF BAROCLINIC ENERGY BY THE AFOREMENTIONED STRONG SHORTWAVE TROUGH SHOULD HELP TO INTENSIFY HELENE AS INDICATED BY ALL OF THE MODELS. FORECAST POSITIONS AND MAX WINDS INITIAL 23/0900Z 37.2N 48.2W 60 KT 12HR VT 23/1800Z 38.2N 44.8W 60 KT...BECOMING EXTRATROPICAL 24HR VT 24/0600Z 39.7N 40.3W 65 KT...EXTRATROPICAL 36HR VT 24/1800Z 41.5N 35.8W 65 KT...EXTRATROPICAL 48HR VT 25/0600Z 43.3N 31.7W 60 KT...EXTRATROPICAL 72HR VT 26/0600Z 46.8N 23.9W 55 KT...EXTRATROPICAL 96HR VT 27/0600Z 50.4N 16.5W 45 KT...EXTRATROPICAL 120HR VT 28/0600Z 55.0N 10.0W 40 KT...EXTRATROPICAL $$ FORECASTER STEWART |
