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Tropical Storm MELISSA Forecast Discussion Number 10

2013-11-20 21:36:38| National Hurricane Center (Atlantic)

Issued at 500 PM AST WED NOV 20 2013 000 WTNT44 KNHC 202036 TCDAT4 TROPICAL STORM MELISSA DISCUSSION NUMBER 10 NWS NATIONAL HURRICANE CENTER MIAMI FL AL142013 500 PM AST WED NOV 20 2013 THE CLOUD PATTERN HAS NOT CHANGED SIGNIFICANTLY SINCE THIS MORNING. THERE IS AN AREA OF DEEP CONVECTION NEAR THE CENTER WHICH IS WRAPPED BY A FEW CYCLONICALLY CURVED BANDS. A PARTIAL ASCAT PASS EARLIER TODAY SUPPORTS AN INITIAL INTENSITY OF 45 KNOTS...AND ALSO INDICATES THAT THE WIND FIELD IS ASYMMETRIC WITH THE LARGEST AREA OF TROPICAL-STORM-FORCE WINDS IN THE SOUTHEAST QUADRANT. DVORAK T-NUMBERS FROM BOTH TAFB AND SAB HAVE BEGUN TO COME DOWN A LITTLE SUPPORTING THE REDUCTION OF THE WINDS. MELISSA IS MOVING OVER PROGRESSIVELY COLDER WATERS AND EMBEDDED WITHIN THE MID-LATITUDE WESTERIES. ALTHOUGH LITTLE CHANGE IN INTENSITY IS ANTICIPATED... MELISSA IS EXPECTED TO ACQUIRE EXTRATROPICAL CHARACTERISTICS IN ABOUT 24-36 HOURS. MELISA CONTINUES TO MOVE TOWARD THE EAST-NORTHEAST OR 060 DEGREES AT 26 KNOTS WHILE EMBEDDED WITHIN THE FLOW AHEAD OF A MID-LATITUDE TROUGH. SINCE THIS STEERING PATTERN IS NOT FORECAST TO CHANGE MUCH...THE NHC FORECAST KEEPS MELISSA ON THIS GENERAL TRACK WITH A GRADUAL TURN TO THE EAST UNTIL DISSIPATION IN ABOUT 4 DAYS OR SOONER. THE NHC FOREAST IS CONSISTENT WITH THE TRACK GUIDANCE AND IS CLOSE TO THE MULTI-MODEL CONSENSUS. FORECAST POSITIONS AND MAX WINDS INIT 20/2100Z 37.2N 44.9W 45 KT 50 MPH 12H 21/0600Z 39.0N 40.5W 45 KT 50 MPH 24H 21/1800Z 41.0N 34.0W 45 KT 50 MPH...POST-TROPICAL 36H 22/0600Z 42.0N 28.0W 45 KT 50 MPH...POST-TROP/EXTRATROP 48H 22/1800Z 43.5N 23.0W 45 KT 50 MPH...POST-TROP/EXTRATROP 72H 23/1800Z 42.0N 17.0W 35 KT 40 MPH...POST-TROP/EXTRATROP 96H 24/1800Z...DISSIPATED $$ FORECASTER AVILA

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Tropical Storm MELISSA Forecast Discussion Number 9

2013-11-20 15:34:46| National Hurricane Center (Atlantic)

Issued at 1100 AM AST WED NOV 20 2013 000 WTNT44 KNHC 201434 TCDAT4 TROPICAL STORM MELISSA DISCUSSION NUMBER 9 NWS NATIONAL HURRICANE CENTER MIAMI FL AL142013 1100 AM AST WED NOV 20 2013 MELISSA HAS MADE THE EXPECTED TRANSITION TO TROPICAL STORM STATUS. DEEP CONVECTION HAS NOW DEVELOPED NEAR THE CENTER...THE CLOUD PATTERN EXHIBITS CURVED BANDS WITH UPPER-LEVEL ANTICYCLONIC OUTFLOW...AND THE UPPER-LEVEL LOW OVER MELISSA HAS WEAKENED. DVORAK ESTIMATES FROM BOTH TAFB AND SAB ALSO CHANGED FROM SUBTROPICAL TO TROPICAL STATUS AND SUPPORT AN INITIAL INTENSITY OF 50 KNOTS. MELISSA IS MOVING OVER PROGRESSIVELY COLDER WATERS AND EMBEDDED WITHIN STRONG SHEAR. THEREFORE...LITTLE CHANGE IN INTENSITY IS ANTICIPATED TODAY...BUT MELISSA SHOULD BEGIN TO GRADUALLY ACQUIRE EXTRATROPICAL CHARACTERISTICS IN ABOUT 24 TO 36 HOURS. THE STORM IS NOW ACCELERATING WITHIN THE SOUTHWESTERLY FLOW AHEAD OF A MID-LATITUDE TROUGH...AND THE INITIAL MOTION IS 060 DEGREES AT 26 KNOTS. THE STEERING FLOW IS NOT FORECAST TO CHANGE MUCH AND THIS PATTERN WILL KEEP MELISSA ON THIS GENERAL TRACK UNTIL DISSIPATION IN ABOUT 4 DAYS. THE NHC FOREAST FOLLOWS THE TRACK GUIDANCE...WHICH IN FACT IS TIGHTLY CLUSTERED AT LEAST FOR THE NEXT 24 TO 36 HOURS. FORECAST POSITIONS AND MAX WINDS INIT 20/1500Z 35.6N 47.7W 50 KT 60 MPH 12H 21/0000Z 37.6N 43.2W 50 KT 60 MPH 24H 21/1200Z 40.0N 37.0W 50 KT 60 MPH 36H 22/0000Z 41.5N 31.0W 45 KT 50 MPH...POST-TROPICAL 48H 22/1200Z 42.5N 24.5W 45 KT 50 MPH...POST-TROP/EXTRATROP 72H 23/1200Z 42.0N 18.5W 40 KT 45 MPH...POST-TROP/EXTRATROP 96H 24/1200Z...DISSIPATED $$ FORECASTER AVILA

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Subtropical Storm MELISSA Forecast Discussion Number 8

2013-11-20 09:36:49| National Hurricane Center (Atlantic)

Issued at 500 AM AST WED NOV 20 2013 000 WTNT44 KNHC 200836 TCDAT4 SUBTROPICAL STORM MELISSA DISCUSSION NUMBER 8 NWS NATIONAL HURRICANE CENTER MIAMI FL AL142013 500 AM AST WED NOV 20 2013 A SMALL AREA OF DEEP CONVECTION HAS BEEN PERSISTING NEAR AND TO THE NORTH OF THE CENTER OF MELISSA SINCE ABOUT 0400 UTC. THIS SUGGESTS THAT MELISSA COULD BE NEARING THE EXPECTED TRANSITION FROM A SUBTROPICAL TO A TROPICAL STORM. NONETHELESS...THE STRENGTH OF THE CYCLONE HAS NOT CHANGED...BASED ON A SATELLITE INTENSITY ESTIMATE FROM TAFB AND EARLIER ASCAT DATA. THE ENVIRONMENTAL CONDITIONS ARE NOT CONDUCIVE FOR STRENGTHENING...AS MELISSA IS EXPECTED TO MOVE OVER PROGRESSIVELY COLDER WATER AND REMAIN IN AT LEAST MODERATE SOUTH-SOUTHWESTERLY SHEAR. THEREFORE...THE NHC FORECAST CALLS FOR LITTLE CHANGE IN INTENSITY DURING THE NEXT FEW DAYS...FOLLOWING THE GFS AND ECMWF GUIDANCE. POST-TROPICAL TRANSITION IS EXPECTED TO OCCUR IN 24 TO 36 HOURS...WHEN THE CYCLONE IS FORECAST TO BE OVER SEA SURFACE TEMPERATURES BELOW 20C. MELISSA IS ACCELERATING TO THE NORTHEAST...AND THE LATEST INITIAL MOTION ESTIMATE IS 055/20. A CONTINUED FAST NORTHEASTWARD TO EAST-NORTHEASTWARD MOTION IS EXPECTED DURING THE NEXT COUPLE OF DAYS WHILE MELISSA REMAINS EMBEDDED IN THE STRONG FLOW TO THE SOUTHEAST OF A LARGE EXTRATROPICAL CYCLONE. DISSIPATION IS NOW PREDICTED TO OCCUR IN 4 DAYS...IN AGREEMENT WITH MOST OF THE GLOBAL MODEL GUIDANCE. FORECAST POSITIONS AND MAX WINDS INIT 20/0900Z 34.8N 50.2W 45 KT 50 MPH 12H 20/1800Z 36.8N 46.4W 45 KT 50 MPH 24H 21/0600Z 39.3N 40.2W 45 KT 50 MPH 36H 21/1800Z 41.4N 34.0W 45 KT 50 MPH...POST-TROPICAL 48H 22/0600Z 43.0N 28.0W 45 KT 50 MPH...POST-TROP/EXTRATROP 72H 23/0600Z 45.0N 22.0W 40 KT 45 MPH...POST-TROP/EXTRATROP 96H 24/0600Z...DISSIPATED $$ FORECASTER CANGIALOSI

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Subtropical Storm MELISSA Forecast Discussion Number 7

2013-11-20 03:38:07| National Hurricane Center (Atlantic)

Issued at 1100 PM AST TUE NOV 19 2013 000 WTNT44 KNHC 200238 TCDAT4 SUBTROPICAL STORM MELISSA DISCUSSION NUMBER 7 NWS NATIONAL HURRICANE CENTER MIAMI FL AL142013 1100 PM AST TUE NOV 19 2013 THE SATELLITE APPEARANCE OF MELISSA IS LESS IMPRESSIVE THAN A FEW HOURS AGO...WITH JUST A SMALL AREA OF CONVECTION FORMING NEAR AND NORTHEAST OF THE CENTER. THE SYSTEM DOES NOT APPEAR TO BE ANY MORE TROPICAL THAN EARLIER...SO IT IS BEING KEPT AS A SUBTROPICAL STORM. THE INITIAL INTENSITY IS LOWERED TO 45 KT IN ACCORDANCE WITH ASCAT DATA AND THE LATEST TAFB SATELLITE ESTIMATE. ALTHOUGH MELISSA IS FORECAST TO MOVE OVER COLDER WATERS SOON...A LARGE INCREASE IN FORWARD SPEED AND SOME NON-TROPICAL FORCING COULD OFFSET THE DECREASING WATER TEMPERATURES. THUS LITTLE CHANGE IN STRENGTH IS FORECAST FOR THE NEXT 48 HOURS...WHICH IS LOWER THAN THE PREVIOUS NHC PREDICTION...AND IS NEAR THE MODEL CONSENSUS. MELISSA COULD STILL BECOME A TROPICAL STORM IN THE NEXT DAY OR SO BEFORE MOVING OVER COLDER WATERS. SOME WEAKENING IS FORECAST AFTER 48 HOURS DUE TO EXTREMELY COLD WATER AND LOSS OF BAROCLINIC FORCING. MELISSA IS EXPECTED TO TRANSITION INTO A POST-TROPICAL CYCLONE WITHIN 36 HOURS DUE TO THE COLDER WATERS...AND INTO AN EXTRATROPICAL CYCLONE IN ABOUT 3 DAYS. THE STORM IS MOVING TO THE NORTHEAST AT ABOUT 15 KT. MODEL GUIDANCE REMAINS IN EXCELLENT AGREEMENT ON MELISSA ACCELERATING TO THE NORTHEAST AND EAST-NORTHEAST OVER THE NEXT 48H AHEAD OF A LARGE MID-LATITUDE TROUGH. THE LATEST CONSENSUS HAS SHIFTED EASTWARD... AND THE NHC FORECAST FOLLOWS SUIT. THE CYCLONE WILL PROBABLY BE ABSORBED BY A LARGER LOW AND/OR ASSOCIATED FRONTAL SYSTEM WITHIN 96 HOURS...IF NOT SOONER. FORECAST POSITIONS AND MAX WINDS INIT 20/0300Z 33.6N 52.4W 45 KT 50 MPH 12H 20/1200Z 35.7N 49.2W 45 KT 50 MPH 24H 21/0000Z 38.4N 43.7W 45 KT 50 MPH 36H 21/1200Z 40.8N 37.7W 45 KT 50 MPH...POST-TROPICAL 48H 22/0000Z 43.0N 31.5W 45 KT 50 MPH...POST-TROP/EXTRATROP 72H 23/0000Z 48.0N 25.0W 40 KT 45 MPH...POST-TROP/EXTRATROP 96H 24/0000Z 54.0N 23.0W 40 KT 45 MPH...POST-TROP/EXTRATROP 120H 25/0000Z...DISSIPATED $$ FORECASTER BLAKE

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Subtropical Storm MELISSA Forecast Discussion Number 6

2013-11-19 21:46:43| National Hurricane Center (Atlantic)

Issued at 500 PM AST TUE NOV 19 2013 000 WTNT44 KNHC 192046 TCDAT4 SUBTROPICAL STORM MELISSA DISCUSSION NUMBER 6 NWS NATIONAL HURRICANE CENTER MIAMI FL AL142013 500 PM AST TUE NOV 19 2013 MELISSA APPEARS TO BE ON THE CUSP OF MAKING THE TRANSITION FROM A SUBTROPICAL TO A TROPICAL CYCLONE. TWO EARLIER ASCAT OVERPASSES CAPTURED THE WIND FIELD IN THE EASTERN SEMICIRCLE...WHICH INDICATED THAT THE OUTER WIND FIELD HAD WEAKENED AND THAT THE INNER-CORE WIND FIELD HAD CONTRACTED INWARD WITH THE RADIUS OF MAXIMUM WINDS NOW AT ABOUT 40-50 NMI. IN ADDITION...AN 1119 UTC AMSU OVERPASS SHOWED THAT A PRONOUNCED UPPER-LEVEL WARM CORE HAD DEVELOPED OVER THE LOW-LEVEL CENTER. THESE SATELLITE INDICATORS WOULD SUGGEST THAT MELISSA WAS NOW A TROPICAL CYCLONE. HOWEVER...THE AMSU DATA ALSO REVEALED THAT THERE WAS STILL A STRATOSPHERIC CONNECTION TO THE WARM CORE. THIS...PLUS THE LACK OF ANY DEEP CONVECTION NEAR THE WELL-DEFINED LOW-LEVEL CENTER...ARGUES FOR KEEPING MELISSA A SUBTROPICAL STORM. SINCE THE ASCAT PASSES MISSED THE WESTERN SEMICIRCLE WHERE THE STRONGEST WINDS WERE LIKELY OCCURRING IN SOME VIGOROUS CONVECTION...THE INTENSITY IS BEING MAINTAINED AT 55 KT BASED ON A SUBTROPICAL SATELLITE CLASSIFICATION FROM TAFB...AND EARLIER 53-56 KT AMSU INTENSITY ESTIMATES FROM CIRA AND CIMSS. THE INITIAL MOTION ESTIMATE IS NOW 040/14 KT. MELISSA HAS FINALLY MADE THE MUCH ANTICIPATED TURN TO THE NORTHEAST AHEAD OF A STRONG COLD FRONT AND ASSOCIATED DEEP-LAYER TROUGH. NHC MODEL GUIDANCE IS IN EXCELLENT AGREEMENT ON THE CYCLONE ACCELERATING NORTHEASTWARD OVER THE NEXT 2-3 DAYS BEFORE TURNING NORTHWARD AND MERGING WITH A FRONTAL SYSTEM IN 4-5 DAYS OVER THE FAR NORTH ATLANTIC. THE OFFICIAL FORECAST TRACK WAS SHIFTED TO THE RIGHT OF THE PREVIOUS ADVISORY TRACK AFTER 36 HOURS...AND LIES CLOSE TO THE MULTI-MODEL CONSENSUS TVCA AND THE FLORIDA STATE SUPERENSEMBLE MODEL. THE VERTICAL SHEAR HAS DROPPED SHARPLY TO ABOUT 7 KT...WHICH HAS ALLOWED THE LOW- AND MID-/UPPER-LEVEL CIRCULATION CENTERS TO FINALLY BECOME VERTICALLY ALIGNED. THE ONLY THING PREVENTING MELISSA FROM MAKING THE TRANSITION TO A TROPICAL CYCLONE IS THE LACK OF SIGNIFICANT DEEP CONVECTION ORGANIZING AROUND THE LOW-LEVEL CENTER. HOWEVER...SHALLOW TO MODERATE CONVECTION HAS BEEN DEVELOPING NEAR THE CENTER AND IN THE DRY SLOT IN THE EASTERN SEMICIRCLE DURING THE PAST COUPLE OF HOURS...AND ONLY A SLIGHT INCREASE IN THE DEPTH AND COVERAGE OF THE CONVECTION WOULD ALLOW MELISSA TO STRENGTHEN SLIGHTLY AND ALSO QUICKLY TRANSITION TO A TROPICAL STORM. THE CYCLONE IS EXPECTED TO MOVE OVER COOLER WATER AND INTO A DRIER AND MORE STABLE AIRMASS IN 24-36 HOURS...WHICH SHOULD INDUCE STEADY WEAKENING. BY 48 HOURS...INCREASING VERTICAL WIND SHEAR SHOULD ENHANCE THE WEAKENING PROCESS AND ALSO CAUSE MELISSA TO TRANSITION TO A POST-TROPICAL EXTRATROPICAL CYCLONE. THE FORECAST CLOSELY FOLLOWS THE INTENSITY CONSENSUS MODEL ICON. TRACK...INTENSITY... AND WIND RADII FORECASTS DURING THE EXTRATROPICAL STAGE WERE COORDINATED WITH THE NOAA OCEAN PREDICTION CENTER. FORECAST POSITIONS AND MAX WINDS INIT 19/2100Z 33.0N 53.7W 55 KT 65 MPH 12H 20/0600Z 34.9N 51.4W 60 KT 70 MPH 24H 20/1800Z 37.4N 46.7W 55 KT 65 MPH 36H 21/0600Z 40.1N 41.1W 50 KT 60 MPH 48H 21/1800Z 42.4N 35.4W 50 KT 60 MPH...POST-TROP/EXTRATROP 72H 22/1800Z 47.0N 26.0W 45 KT 50 MPH...POST-TROP/EXTRATROP 96H 23/1800Z 53.5N 24.5W 40 KT 45 MPH...POST-TROP/EXTRATROP 120H 24/1800Z...DISSIPATED $$ FORECASTER STEWART

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