000 AXNT20 KNHC 201758 TWDAT TROPICAL WEATHER DISCUSSION NWS NATIONAL HURRICANE CENTER MIAMI FL 105 PM EST TUE DEC 20 2011 TROPICAL WEATHER DISCUSSION FOR NORTH AMERICA...CENTRAL AMERICA...GULF OF MEXICO...CARIBBEAN SEA...NORTHERN SECTIONS OF SOUTH AMERICA...AND ATLANTIC OCEAN TO THE AFRICAN COAST FROM THE EQUATOR TO 32N. THE FOLLOWING INFORMATION IS BASED ON SATELLITE IMAGERY...WEATHER OBSERVATIONS...RADAR...AND METEOROLOGICAL ANALYSIS. BASED ON 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 1700 UTC. ...THE ITCZ/THE MONSOON TROUGH... THE MONSOON TROUGH EXTENDS INLAND OVER W AFRICA TO THE COAST OF SRN SIERRA LEONE NEAR 7N13W CONTINUING TO 7N18W. THE ITCZ CONTINUES FROM 7N18W ALONG 4N31W 4N49W. SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS FROM 3N-6N BETWEEN 17W-28W...AND FROM 3N-5N BETWEEN 37W-48W. ...DISCUSSION... GULF OF MEXICO... SURFACE RIDGING DOMINATES THE MAJORITY OF THE GULF OF MEXICO TODAY WITH AXIS EXTENDING FROM A 1027 MB HIGH IN THE W ATLC NEAR 31N71W. HOWEVER...A COLD FRONT IS JUST EMERGING OFF THE COAST OF TEXAS AS OF 1500 UTC EXTENDING FROM SW LOUISIANA NEAR 30N94W REMAINING PARALLEL TO THE COASTLINE TO NEAR 27N97W AND MOVING INLAND OVER THE SRN TIP OF TEXAS AND NRN MEXICO TO NEAR 25W101W. RADAR IMAGERY INDICATES A STRONG LINE OF SHOWERS/THUNDERSTORMS ALONG THE FRONT AXIS WITH A FEW ISOLATED SHOWERS BOTH FARTHER AHEAD AND BEHIND THE AXIS. NLY WINDS UP TO 20 KTS ARE ALSO BEHIND THE FRONT WITH MOSTLY SE-S WINDS OF 15-20 KTS ACROSS THE REMAINDER OF THE BASIN AROUND THE RIDGE. RADAR AND SATELLITE IMAGERY ARE ALSO INDICATING A FEW OTHER AREAS OF ISOLATED SHOWERS ACROSS THE BASIN INCLUDING PORTIONS OF THE CENTRAL GULF BETWEEN 85W-89W. ALOFT...UPPER LEVEL RIDGING IS OVER THE ERN HALF OF THE BASIN WHILE AN UPPER LEVEL TROUGH IS COVERING THE CENTRAL CONUS TO THE NW CORNER SUPPORTING THE FRONTAL BOUNDARY. THE FRONT IS EXPECTED TO SLOWLY MOVE EWD OVER THE NEXT 24 HOURS BEFORE STALLING AND RETREATING BACK TO THE NW BEFORE A SECOND FRONT MOVES OFF THE COAST ON THURSDAY. CARIBBEAN SEA... A DISSIPATING COLD FRONT IS LYING ACROSS THE NE CARIBBEAN ISLANDS ALONG 19N BETWEEN 62W-73W PRODUCING ISOLATED SHOWERS WITHIN 50 NM EITHER SIDE THE AXIS. THE FRONT IS EXPECTED TO STALL AND CONTINUE DISSIPATING OVER THE NEXT 24 HOURS. THE REMAINDER OF THE BASIN IS DOMINATED BY NE-E TRADEWIND FLOW OF MAINLY 20 KTS WITH AREAS OF 25 KT WINDS N OF COLOMBIA. ISOLATED SHOWERS ARE EMBEDDED WITHIN THE TRADEWIND FLOW BASIN-WIDE. ENHANCED CONVECTION IN THE SW CARIBBEAN DUE TO THE MONSOON TROUGH HAS DIMINISHED COMPARED TO THE PAST FEW DAYS...BUT AMPLE MOISTURE REMAINS PRESENT. ALOFT...AN UPPER LEVEL RIDGE EXTENDS FROM VENEZUELA TO CUBA AND UP THE ERN UNITED STATES SEABOARD. PATCHES OF UPPER LEVEL MOISTURE ARE BEING DRAWN AROUND THE UPPER RIDGE SUPPORTING A FEW HIGH CLOUDS. EXPECT STRONG TRADEWIND FLOW TO REMAIN ACROSS MUCH OF THE BASIN AS HIGH PRESSURE OVER THE WRN ATLC CONTINUES TO CREATE A STRONG PRESSURE GRADIENT. ATLANTIC OCEAN... SURFACE RIDGING AROUND A 1027 MB HIGH NEAR 31N71W IS PROVIDING MOSTLY FAIR WEATHER ACROSS THE WRN ATLC. THE RIDGE IS SUPPORTED BY AN UPPER LEVEL RIDGE WITH AXIS ALONG 76W. AN UPPER LEVEL TROUGH TO THE E CONTINUES TO SUPPORT A LARGE COLD FRONT IMPACTING THE CENTRAL ATLC ALONG 32N42W 24N49W 19N62W BECOMING DISSIPATING TO 19N73W. ISOLATED SHOWERS ARE WITHIN 75 NM BEHIND THE FRONT WITH AN AREA OF SCATTERED SHOWERS AHEAD OF THE FRONT N OF 25N BETWEEN 37W-43W. TO THE S...A SURFACE TROUGH IS ALONG 14N53W TO 11N58W SUPPORTING SCATTERED SHOWERS/POSSIBLE THUNDERSTORMS FROM 11N-13N BETWEEN 54W-63W. THESE SHOWERS MAY DRIFT WWD AND IMPACT THE SRN WINDWARD ISLANDS. THE REMAINDER OF THE BASIN IS INFLUENCED BY SURFACE RIDGING AROUND A 1036 MB HIGH NE OF THE AZORES ISLANDS NEAR 40N22W PROVIDING GENERALLY FAIR WEATHER ACROSS THE ERN ATLC. ALOFT...AN UPPER LEVEL RIDGE CENTERED OVER THE AZORES ISLANDS IS SUPPORTING THE SURFACE RIDGE. A CUT-OFF UPPER LEVEL LOW IS CENTERED TO THE S NEAR 23N26W CAUSING NO SIGNIFICANT WEATHER BESIDES A FEW UPPER LEVEL CLOUDS NEAR THE AFRICAN COAST N OF THE ITCZ. A SHORTWAVE UPPER TROUGH OVER THE NW ATLC IS SUPPORTING A COLD FRONT ENTERING THE DISCUSSION AREA ALONG 32N54W 26N58W 22N67W 22N76W AND DISSIPATING TO CENTRAL CUBA. GALE FORCE WINDS ARE NOTED N OF 29N BEHIND THE FRONT. DUE TO DRY AIR ALOFT...ISOLATED SHOWERS ARE ONLY WITHIN 60 NM AHEAD OF THE AXIS WITH WIDESPREAD STRATOCUMULUS CLOUDS BEHIND IT. A PRE-FRONTAL TROUGH IE E OF THE FRONT ALONG 50W N OF 25N. POSSIBLE ISOLATED SHOWERS ARE ALONG THE TROUGH AXIS. A SURFACE RIDGE IS BUILDING IN BEHIND THE FRONT CURRENTLY ANCHORED AROUND A 1030 MB HIGH JUST OFFSHORE OF NORTH CAROLINA. FARTHER S IN THE TROPICAL ATLC...A SURFACE TROUGH IS ALONG 14N52W TO 9N56W. SCATTERED SHOWERS ARE WITHIN 200 NM NW OF THE AXIS. THE REMAINDER OF THE ERN ATLC IS UNDER THE INFLUENCE OF SURFACE RIDGING AROUND A 1034 MB HIGH OVER THE AZORES ISLANDS. ALOFT...AN UPPER LEVEL RIDGE IS CENTERED NEAR 34N25W SUPPORTING THE SURFACE RIDGE. A WEAK SHORTWAVE UPPER TROUGH IS ALONG 33N42W TO 21N32W CAUSING LITTLE SIGNIFICANT WEATHER. EXPECT THE FRONTAL SYSTEM IN THE CENTRAL ATLC TO MOVE NE OVER THE NEXT SEVERAL DAYS. FOR ADDITIONAL INFORMATION PLEASE VISIT HTTP://WWW.HURRICANES.GOV/MARINE $$ WALTON