Subtropical Storm MELISSA

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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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