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| #219294 (Received by flhurricane at: 4:43 AM 29.Sep.2008) TCDAT2 SUBTROPICAL STORM LAURA DISCUSSION NUMBER 1 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL122008 500 AM EDT MON SEP 29 2008 DURING THE PAST 6 HOURS...CONVENTIONAL SATELLITE IMAGERY INDICATES DEEP CONVECTION WITH CLOUD TOPS TO NEAR -70C HAS CONTINUED TO INCREASE AND HAS STARTED WRAPPING AROUND AND VERY NEAR THE CENTER OF THE LARGE NON-TROPICAL LOW PRESSURE SYSTEM LOCATED ABOUT 775 NMI WEST OF THE WESTERNMOST AZORES ISLANDS. THERE IS ENOUGH CONVECTION NEAR THE CENTER NOW FOR THIS SYSTEM TO BE CLASSIFIED AS A SUBTROPICAL STORM. THE 06Z SATELLITE CLASSIFICATION FROM TAFB WAS ST3.0/45 KT...BUT USING THE DVORAK TECHNIQUE FOR A TROPICAL SYSTEM YIELDS NEARLY EIGHT TENTHS BANDING...OR T3.5/55 KT. SO THE INITIAL INTENSITY IS BEING SET AT 50 KT...WHICH IS CONSISTENT WITH A FEW 50-KT WIND VECTORS NOTED IN THE NORTHWEST QUADRANT IN A 28/2133Z QUIKSCAT HI-RES OVERPASS. HOWEVER...SINCE THE TIME OF THAT OVERPASS... CONVECTION HAS INCREASED MARKEDLY AND IS NOW THE SOLID BAND OF CONVECTION IN THE SOUTHERN SEMICIRCLE. THEREFORE...IT IS POSSIBLE THAT THE INITIAL INTENSITY COULD BE A LITTLE HIGHER THAN CURRENTLY INDICATED. THE INITIAL MOTION ESTIMATE IS 285/7. ALL OF THE NHC MODEL GUIDANCE IS IN GOOD AGREEMENT ON SUBTROPICAL STORM LAURA MOVING TO THE WEST-NORTHWEST FOR THE NEXT 12 HOURS OR SO...AND THEN TURNING TOWARD THE NORTHWEST AND NORTH AND ACCELERATING AS THE INCIPIENT MID-LEVEL CIRCULATION WEAKENS AND OPENS UP INTO A TROUGH AND GETS LIFTED NORTHWARD AROUND THE WESTERN PERIPHERY OF A NORTH-SOUTH ORIENTED MID-LEVEL RIDGE ANCHORED OVER THE AZORES ISLANDS. AFTER REACHING THE HIGHER LATITUDES IN ABOUT 72 HOURS...LAURA IS FORECAST TO GET PICKED BY THE FAST WESTERLIES AND MOVE QUICKLY EASTWARD AS AN EXTRATROPICAL STORM SYSTEM. LAURA IS EXPECTED TO REMAIN OVER 25C-26C SSTS FOR THE NEXT 24 HOURS AND ALSO BE UNDER LIGHT TO MODERATE SHEAR CONDITIONS. THEREFORE... SOME ADDITIONAL STRENGTHENING IS FORECAST. HOWEVER...IF THE CURRENT TREND OF CONVECTION WRAPPING AROUND THE CENTER CONTINUES...THEN SUBTROPICAL STORM LAURA COULD QUICKLY TRANSITION OVER TO A TROPICAL CYCLONE AND BECOME A HURRICANE WITH A BANDING EYE FEATURE LATER TODAY. BY 36 HOURS...LAURA IS EXPECTED TO BE MOVING OVER MUCH COOLER WATER...WHICH SHOULD INDUCE WEAKENING ALONG WITH A GRADUAL TRANSITION TO EXTRATROPICAL STATUS. THE OFFICIAL INTENSITY FORECAST IS A BLEND OF THE SHIPS...GFDL...HWRF...AND ICON INTENSITY MODELS. FORECAST POSITIONS AND MAX WINDS INITIAL 29/0900Z 37.2N 47.3W 50 KT 12HR VT 29/1800Z 38.0N 48.3W 55 KT 24HR VT 30/0600Z 39.8N 48.9W 60 KT 36HR VT 30/1800Z 41.7N 48.8W 60 KT...BECOMING EXTRATROPICAL 48HR VT 01/0600Z 44.0N 48.0W 55 KT...EXTRATROPICAL 72HR VT 02/0600Z 51.5N 44.0W 50 KT...EXTRATROPICAL 96HR VT 03/0600Z 58.0N 34.5W 45 KT...EXTRATROPICAL 120HR VT 04/0600Z 57.0N 21.5W 40 KT...EXTRATROPICAL $$ FORECASTER STEWART |
