Subtropical Storm Melissa - 10am Monday Discussion

By: National Hurricane Center
By: National Hurricane Center

SUBTROPICAL STORM MELISSA DISCUSSION NUMBER 1
NWS NATIONAL HURRICANE CENTER MIAMI FL AL142013
1100 AM EDT MON NOV 18 2013

DEEP CONVECTION HAS DEVELOPED DURING THE PAST SEVERAL HOURS NEAR THE WELL-DEFINED CENTER OF A LARGE GALE-AREA LOCATED OVER THE CENTRAL ATLANTIC WELL TO THE EAST-SOUTHEAST OF BERMUDA. FRONTAL BOUNDARIES NEAR THE CENTER APPEAR TO HAVE DISSIPATED AND SO ADVISORIES ARE BEING INITIATED AT THIS TIME. ALTHOUGH THERE ARE HINTS OF ANTICYCLONIC OUTFLOW HAVING RECENTLY DEVELOPED OVER THE INNER CORE CONVECTION...THE SYSTEM IS STILL WELL-EMBEDDED WITHIN AN UPPER-LEVEL LOW AND THE MOST RECENT SCATTEROMETER WIND DATA SUGGEST THAT THE CYCLONE MAY STILL HAVE A LARGE RADIUS OF MAXIMUM WINDS. AS A RESULT...THE SYSTEM IS BEING DESIGNATED AS A SUBTROPICAL STORM RATHER THAN A TROPICAL STORM...AT LEAST FOR NOW.

THE INITIAL MOTION ESTIMATE IS NORTHWESTWARD...OR 320/08 KT. NHC MODEL GUIDANCE IS IN EXCELLENT AGREEMENT ON MELISSA MOVING NORTHWESTWARD AND GRADUALLY SLOWING DOWN OVER THE NEXT 24 HOURS OR SO AS IT MOVES AROUND THE WESTERN PERIPHERY OF A HIGH-AMPLITUDE RIDGE LOCATED BETWEEN THE CYCLONE AND THE AZORES. THE CYCLONE COULD POSSIBLY BECOME STATIONARY FOR A BRIEF PERIOD ON TUESDAY WHEN THE SYSTEM MOVES UNDERNEATH A 200 MB LOW/TROUGH. HOWEVER...BY 48 HORUS AND BEYOND...A DEEP-LAYER TROUGH LOCATED OVER THE EASTERN PORTIONS OF CANADA AND THE UNITED SATES IS EXPECTED TO ACCELERATE MELISSA TO THE NORTHEAST. BY DAYS 4 AND 5...MELISSA IS FORECAST OT INTERACT WITH THE AFOREMENTIONED DEEPENING TROUGH AND TURN BACK TOWARD THE NORTH AND NORTHWEST OVER THE FAR NORTH ATLANTIC. THE OFFICIAL FORECAST TRACK IS CLOSE TO THE MULTI-MODEL CONSENSUS TVCA.

MELISSA HAS ABOUT 48 HOURS OR SO TO STRENGTHEN...AND THE SHIPS INTENSITY MODEL INDICATES THAT THE VERTICAL SHEAR IS EXPECTED TO DECREASE TO LESS THAN 10 KT BY 36 HOURS. THE WEAKENING SHEAR SHOULD ALLOW FOR AT LEAST SOME MODEST STRENGTHENING TO OCCUR WHILE THE CYCLONE REMAINS OVER RELATIVELY WARM WATER...BUT ALSO ALLOW FOR THE TRANSITION TO A TROPICAL CYCLONE. THE NHC INTENSITY FORECAST IS SIMILAR TO THE ICON INTENSITY FORECAST MODEL. HOWEVER...IT IS NOT OUT OF THE QUESTION THAT MELISSA COULD ATTAIN HURRICANE STATUS IN 36-48 HOURS WHEN THE VERTICAL SHEAR IS AT A MINIMUM.


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