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Subtropical Storm MELISSA Forecast Discussion Number 2
2013-11-18 21:54:01| National Hurricane Center (Atlantic)
Issued at 500 PM AST MON NOV 18 2013 000 WTNT44 KNHC 182053 TCDAT4 SUBTROPICAL STORM MELISSA DISCUSSION NUMBER 2 NWS NATIONAL HURRICANE CENTER MIAMI FL AL142013 500 PM AST MON NOV 18 2013 DEEP CONVECTION HAS PERSISTED NEAR THE CENTER OF MELISSA...ALBEIT SOMEWHAT FRAGMENTED. WEAK ANTICYCLONIC OUTFLOW HAS BECOME ESTABLISHED IN THE SOUTHERN SEMICIRCLE OF THE INNER-CORE REGION... SUGGESTING THAT MELISSA IS TRYING TO MAKE THE TRANSITION TO A TROPICAL STORM. IN ADDITION...EARLIER ASCAT OVERPASSES AT 1314Z AND 1408Z INDICATED THAT THE RADIUS OF MAXIMUM WINDS HAS CONTRACTED DOWN TO LESS THAN 80 NMI AND MAXIMUM WINDS WERE 50-51 KT IN THE SOUTHWESTERN QUADRANT. HOWEVER...BOTH OVERPASSES MISSED THE INNER CORE WIND FIELD...WHICH MEANS THAT THE RADIUS OF MAXIMUM WINDS COULD BE SMALLER AND THE PEAK WINDS COULD BE STRONGER. AFTER MELISSA PASSED JUST EAST OF DRIFTING BUOY 41999 AT 1000Z...WHICH REPORTED A PRESSURE OF 989.4 MB...THE PRESSURE AT THE BUOY HAS REMAINED AT OR BELOW 993 MB SINCE ABOUT 1400Z AS MELISSA HAS MOVED FARTHER AWAY...WHICH SUGGESTS THAT THE CYCLONE COULD STILL BE DEEPENING. THE INITIAL MOTION ESTIMATE IS 325/08 KT. THERE IS NO SIGNIFICANT CHANGE TO THE PREVIOUS FORECAST TRACK OR REASONING THROUGH 36 H. NHC MODEL GUIDANCE REMAINS IN EXCELLENT AGREEMENT ON MELISSA MOVING SLOWLY NORTHWESTWARD AND NORTHWARD OVER THE NEXT 24 HOURS...AND THEN ACCELERATING NORTHEASTWARD BY 36 H. MELISSA WILL LIKELY REMAIN A SEPARATE ENTITY THROUGH 120 H AND NOT BE ABSORBED BY AN APPROACHING FRONTAL SYSTEM UNTIL NEAR OR AFTER THE FORECAST PERIOD. THE OFFICIAL FORECAST TRACK IS SIMILAR TO THE PREVIOUS ADVISORY AND LIES CLOSE TO THE MULTI-MODEL CONSENSUS TVCA. THE EXTRATROPICAL TRACK IS BASED ON INPUT FROM THE NOAA OCEAN PREDICTION CENTER. MELISSA HAS ABOUT 36 HOURS OR SO TO STRENGTHEN SOME MORE WHILE THE CYCLONE REMAINS OVER RELATIVELY WARM WATER. ALTHOUGH SSTS WILL BE DECREASING FROM THE CURRENT 27C TO AROUND 22-23C BY 36-48 H...THE 500 MB TEMPERATURES ARE NEAR -13C...WHICH IS MUCH COLDER THAN A TYPICAL TROPICAL ATMOSPHERE...AND THAT SHOULD HELP TO MAINTAIN UNSTABLE CONDITIONS AND THE FORMATION OF ADDITONAL CONVECTION IN THE INNER CORE REGION. AS A RESULT...MELISSA IS EXPECTED TO TRANSITION TO A TROPICAL CYCLONE ON TUESDAY. IN ADDITION...THE GFS-BASED SHIPS INTENSITY MODEL IS NOW INDICATING THAT THE 850-200 MB VERTICAL WIND SHEAR WILL DROP SHARPLY FROM THE CURRENT 30 KT TO LESS THAN 10 KT IN THE 18-24 H TIME FRAME...AND THAT IS WHEN THE CYCLONE COULD REACH ITS PEAK INTENSITY...AND POSSIBLY EVEN OBTAIN HURRICANE STRENGTH. GRADUAL WEAKENING IS FORECAST AFTER 48 HOURS AS MELISSA MOVES OVER SSTS LESS THAN 20C...INTO A DRIER AND MORE STABLE AIRMASS...AND EXPERIENCE STRONG SOUTHWESTERLY WIND SHEAR AHEAD OF A DEEP-LAYER TROUGH THAT WILL MOVE OFF OF THE EAST COAST OF NORTH AMERICA DURING THE NEXT DAY OR SO. FORECAST POSITIONS AND MAX WINDS INIT 18/2100Z 29.8N 54.2W 50 KT 60 MPH 12H 19/0600Z 30.7N 54.5W 55 KT 65 MPH 24H 19/1800Z 32.3N 53.5W 60 KT 70 MPH 36H 20/0600Z 34.9N 50.6W 60 KT 70 MPH 48H 20/1800Z 38.0N 46.5W 60 KT 70 MPH 72H 21/1800Z 44.5N 36.0W 55 KT 65 MPH...POST-TROP/EXTRATROP 96H 22/1800Z 50.0N 34.0W 45 KT 50 MPH...POST-TROP/EXTRATROP 120H 23/1800Z 57.0N 39.0W 45 KT 50 MPH...POST-TROP/EXTRATROP $$ FORECASTER STEWART
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