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| #511884 (Received by flhurricane at: 4:44 PM 19.May.2012) TCDAT1 TROPICAL STORM ALBERTO DISCUSSION NUMBER 1 NWS NATIONAL HURRICANE CENTER MIAMI FL AL012012 500 PM EDT SAT MAY 19 2012 SATELLITE...RADAR...AND SURFACE DATA INDICATE THAT THE SMALL SURFACE LOW LOCATED OFF THE COAST OF SOUTH CAROLINA HAS ACQUIRED THE CHARACTERISTICS OF A TROPICAL CYCLONE. ORGANIZED DEEP CONVECTION HAS BEEN PERSISTENT OVER THE CENTER FOR MORE THAN 18 HOURS...AND THE CIRCULATION CENTER HAS BEEN MOVING SOUTH AWAY FROM AN AIRMASS BOUNDARY THAT EXTENDS ROUGHLY ALONG 33N. BASED ON AN ASCAT PASS FROM AROUND 1530 UTC...THE INITIAL INTENSITY IS SET AT 40 KT. ALBERTO IS SITUATED IN A MARGINAL THERMODYNAMIC ENVIRONMENT FOR STRENGTHENING...WITH A MARKEDLY DRY CONTINENTAL AIRMASS TO ITS NORTH AND WEST OVER THE EASTERN CAROLINAS. GIVEN THIS...ONLY MODEST INTENSIFICATION IS EXPECTED DESPITE THE CYCLONE BEING OVER THE RELATIVELY WARM GULF STREAM. ALBERTO IS EXPECTED TO BECOME EXTRATROPICAL BY 96 HOURS...AND SHOULD DISSIPATE BY DAY 5. THE NHC INTENSITY FORECAST IS A BLEND OF THE MORE AGGRESSIVE STATISTICAL GUIDANCE AND THE WEAKER DYNAMICAL MODELS. THE LOW-LEVEL CIRCULATION IS A BIT TO THE EAST OF THE COLDEST CLOUD TOPS AND THE CIRCULATION CENTER SEEN ON RADAR...AND THE INITIAL MOTION ESTIMATE IS 220/03. THE SYNOPTIC ENVIRONMENT IS COMPLEX...AS ALBERTO IS IN A REGION OF WEAK STEERING FLOW WITHIN A BROAD MID/UPPER-LEVEL TROUGH. THE NHC FORECAST SHOWS A SLOW SOUTHWESTWARD MOTION OVER THE NEXT DAY OR SO DUE TO THE STRONG NORTHEASTERLY FLOW BETWEEN A SURFACE RIDGE EAST OF THE APPALACHIANS AND A LARGER EXTRATROPICAL LOW CENTERED NEAR 36N/72W. AS THAT LOW MOVES WESTWARD AND WEAKENS BY SUNDAY NIGHT...ALBERTO IS EXPECTED TO TURN NORTHWARD AND THEN ACCELERATE NORTHEASTWARD AFTER 48 HOURS AS A SHORTWAVE TROUGH MOVES INTO THE EASTERN UNITED STATES AND THE STEERING FLOW BECOMES SOUTHWESTERLY. GIVEN THE SMALL SIZE OF ALBERTO AND THE COMPLEX STEERING PATTERN...IT IS NOT SURPRISING THAT THE TRACK MODEL GUIDANCE SHOWS A LARGE AMOUNT OF SPREAD...BOTH IN TERMS OF HOW FAR SOUTH AND WEST ALBERTO WILL MOVE...AND HOW SHARP THE TURN TOWARD THE NORTHEAST WILL BE. THE NHC TRACK FORECAST IS GENERALLY CLOSE TO THE TVCA MULTI-MODEL CONSENSUS...AND IS OF VERY LOW CONFIDENCE. A TROPICAL STORM WATCH COULD BE REQUIRED FOR A PORTION OF THE COAST OF THE CAROLINAS THIS EVENING. ALBERTO IS EARLIEST-FORMING TROPICAL STORM IN THE ATLANTIC BASIN SINCE ANA IN 2003. THIS IS ALSO THE FIRST TIME THAT A TROPICAL STORM HAS FORMED BEFORE THE OFFICIAL START OF THE HURRICANE SEASON IN BOTH THE ATLANTIC AND EAST PACIFIC BASINS. FORECAST POSITIONS AND MAX WINDS INIT 19/2100Z 32.2N 77.7W 40 KT 45 MPH 12H 20/0600Z 31.9N 78.1W 45 KT 50 MPH 24H 20/1800Z 31.7N 78.5W 45 KT 50 MPH 36H 21/0600Z 31.9N 78.9W 45 KT 50 MPH 48H 21/1800Z 32.7N 78.5W 45 KT 50 MPH 72H 22/1800Z 34.5N 75.5W 45 KT 50 MPH 96H 23/1800Z 37.5N 72.0W 40 KT 45 MPH...POST-TROP/EXTRATROP 120H 24/1800Z...DISSIPATED $$ FORECASTER BRENNAN |
