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| #646150 (Received by flhurricane at: 10:00 PM 18.Nov.2013) TCDAT4 SUBTROPICAL STORM MELISSA DISCUSSION NUMBER 3 NWS NATIONAL HURRICANE CENTER MIAMI FL AL142013 1100 PM AST MON NOV 18 2013 DEEP CONVECTION IN MELISSA REMAINS QUITE ASYMMETRIC WITH A NARROW BAND WRAPPING AROUND THE CENTER AT A RADIUS OF ABOUT 60-90 NM ALONG WITH A LARGER BAND IN THE EASTERN SEMI-CIRCLE A FEW HUNDRED MILES FROM THE CENTER. WATER VAPOR IMAGERY INDICATES THAT MELISSA REMAINS INTERTWINED WITH AN UPPER-LEVEL LOW...THUS A SUBTROPICAL STORM STATUS STILL APPEARS WARRANTED AT THIS TIME. A TIMELY 0030 UTC PARTIAL ASCAT-A PASS PROVIDED PEAK WINDS OF ABOUT 45 KT. THIS ALONG WITH THE TAFB HEBERT-POTEAT SUBTROPICAL CLASSIFICATION OF 3.0...45-50 KT...HELPED TO DETERMINE THE INITIAL INTENSITY OF 50 KT. MELISSA IS MOVING AT 325 DEGREES AT 7 KT. THE CYCLONE SHOULD VEER TOWARD THE NORTHEAST AND ACCELERATE DURING THE NEXT TWO DAYS AS A SHORTWAVE TROUGH OVER EASTERN CANADA CURRENT HELPS KICK OUT MELISSA INTO THE MID-LATITUDE WESTERLIES. THE TRACK GUIDANCE IS TIGHTLY CLUSTERED THROUGH 72 HR...BUT THEN DIVERGES DEPENDING IN PART ON HOW MUCH EXTRATROPICAL TRANSITION OCCURS. THE GFS AND DEPENDENT MESOSCALE HURRICANE MODELS INDICATE AN EARLIER TRANSITION...WHICH THEN WRAPS MELISSA NORTHWARD QUICKER. THE ECMWF AND NAVGEM KEEP MELISSA FARTHER EAST IN THE WARM SECTOR OF THE APPROACHING EXTRATROPICAL LOW AND DISSIPATE IT BEFORE EXTRATROPICAL TRANSITION. THE OFFICIAL FORECAST IS A BLEND OF THESE SOLUTIONS AND IS CLOSE TO THE PREVIOUS ADVISORY THROUGH THREE DAYS...BUT THEN FASTER AND FARTHER EAST THEREAFTER. THE EXTRATROPICAL TRACK IS BASED IN LARGE PART UPON INPUT FROM THE OCEAN PREDICTION CENTER. MELISSA HAS A SHORT WINDOW OF OPPORTUNITY FOR FURTHER INTENSIFICATION. THE SHEAR IS PROJECTED TO LESSEN FOR ABOUT A DAY WHILE THE CYCLONE REMAINS OVER LUKEWARM WATERS. THIS SHOULD ALLOW ENOUGH CONVECTION TO FORM OVER THE CENTER AND A DEEP WARM CORE TO DEVELOP FOR TROPICAL TRANSITION TO OCCUR...AS ALSO INDICATED BY THE FSU CYCLONE PHASE SPACE DIAGRAMS. IN ABOUT 36 TO 48 HOURS...THE RAPIDLY DROPPING SSTS THAT MELISSA WILL ENCOUNTER COUPLED WITH MUCH STRONGER VERTICAL SHEAR SHOULD CAUSE THE DEEP CONVECTION TO CEASE. THUS A TRANSITION TO A POST-TROPICAL LOW IS INDICATED AT 48 HOURS...EVEN THOUGH A FULL EXTRATROPICAL STAGE IS PREDICTED TO OCCUR AROUND THREE DAYS. BY DAY FIVE...MELISSA IS ANTICIPATED TO BECOME ABSORBED BY THE LARGER EXTRATROPICAL LOW. THE AFOREMENTIONED ASCAT PASS ALSO ALLOWED FOR A MORE CONFIDENT ASSESSMENT OF THE 34 AND 50 KT WIND RADII. FORECAST POSITIONS AND MAX WINDS INIT 19/0300Z 30.3N 54.7W 50 KT 60 MPH 12H 19/1200Z 31.3N 54.5W 50 KT 60 MPH 24H 20/0000Z 33.6N 52.4W 55 KT 65 MPH 36H 20/1200Z 36.4N 48.5W 60 KT 70 MPH 48H 21/0000Z 39.8N 43.4W 55 KT 65 MPH...POST-TROPICAL 72H 22/0000Z 46.0N 33.5W 50 KT 60 MPH...POST-TROP/EXTRATROP 96H 23/0000Z 53.5N 33.0W 40 KT 45 MPH...POST-TROP/EXTRATROP 120H 24/0000Z...DISSIPATED $$ FORECASTER LANDSEA |
