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| #219385 (Received by flhurricane at: 4:34 PM 29.Sep.2008) TCDAT2 SUBTROPICAL STORM LAURA DISCUSSION NUMBER 3 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL122008 500 PM EDT MON SEP 29 2008 AN ASCAT PASS AROUND 1326 UTC THIS MORNING INDICATED MAXIMUM WINDS NEAR 45 KT...BUT THIS SENSOR USUALLY TENDS TO HAVE A SLIGHT LOW BIAS SO AN INTENSITY OF 50 KT WILL BE MAINTAINED IN THIS PACKAGE. LAURA CONTINUES TO ACQUIRE SOME TROPICAL CHARACTERISTICS...WITH THE FSU PHASE SPACE DIAGRAMS AND AMSU DATA BOTH INDICATING A DEEP WARM CORE. ON THE OTHER HAND...THE ASSOCIATED CONVECTION IS NOT ALL THAT DEEP AND THE 75 NM RADIUS OF MAXIMUM WINDS IS IN THE GRAY ZONE BETWEEN TROPICAL AND SUBTROPICAL. LAURA WILL CONTINUE TO BE CLASSIFIED AS A SUBTROPICAL STORM FOR NOW ALTHOUGH THE TRANSITION TO A TROPICAL CYCLONE IS LIKELY OCCURRING. LATEST SATELLITE FIXES INDICATE THAT LAURA IS TURNING AND ACCELERATING WITH AN INITIAL MOTION OF 335/8. THE TRACK FORECAST REASONING HAS NOT CHANGED. ALTHOUGH SOME OF THE MODELS...INCLUDING THE GFS...GFDL...AND ECMWF...HAVE SHIFTED LEFT SINCE THIS MORNING...THE OFFICIAL FORECAST LIES VERY CLOSE TO THE MODEL CONSENSUS AND IS NOT FAR FROM THE PREVIOUS FORECAST. IF LAURA IS BECOMING MORE TROPICAL...IT HAS A CHANCE TO STRENGTHEN A LITTLE BEFORE IT MOVES OVER COLDER WATERS. THE OFFICIAL FORECAST FOLLOWS CLOSE TO THE SHIPS AND LGEM MODELS FOR THE FIRST 36 HOURS BUT THEN CALLS FOR GRADUAL WEAKENING ONCE LAURA BECOMES EXTRATROPICAL AND MOVES INTO A COLDER AIR MASS...MUCH LIKE AN OCCLUDED LOW. THE OFFICIAL FORECAST IS IN BEST AGREEMENT WITH THE GFDL AND HWRF GUIDANCE. LAURA WILL BEGIN EXTRATROPICAL TRANSITION BY 36 HOURS AND THEN COULD BE FULLY ABSORBED INTO A FRONTAL ZONE BY DAY 5 WEST OF IRELAND...ALTHOUGH A POINT AT THAT TIME IS STILL GIVEN FOR CONTINUITY. FORECAST POSITIONS AND MAX WINDS INITIAL 29/2100Z 38.3N 48.4W 50 KT 12HR VT 30/0600Z 39.3N 48.6W 55 KT 24HR VT 30/1800Z 41.2N 48.3W 60 KT 36HR VT 01/0600Z 43.6N 47.4W 55 KT 48HR VT 01/1800Z 46.5N 46.0W 50 KT...EXTRATROPICAL 72HR VT 02/1800Z 52.5N 41.0W 50 KT...EXTRATROPICAL 96HR VT 03/1800Z 55.0N 28.0W 45 KT...EXTRATROPICAL 120HR VT 04/1800Z 55.0N 12.0W 45 KT...EXTRATROPICAL $$ FORECASTER BERG/FRANKLIN |
