000 AXNT20 KNHC 180556 TWDAT TROPICAL WEATHER DISCUSSION NWS NATIONAL HURRICANE CENTER MIAMI FL 105 AM EST SUN DEC 18 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 0000 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 0515 UTC. ...ITCZ/MONSOON TROUGH... THE INTERTROPICAL CONVERGENCE ZONE AXIS EXTENDS FROM 08N13W TO 07N30W TO 07N47W. SCATTERED MODERATE CONVECTION IS FROM 05N-09N BETWEEN 30W-44W. ...DISCUSSION... GULF OF MEXICO... UPPER LEVEL CONFLUENCE IS NOTED ACROSS THE GULF THIS EVENING AS AN UPPER LEVEL LONGWAVE TROUGH REMAINS TO THE NORTH ACROSS THE SE CONUS AND AN UPPER LEVEL RIDGE REMAINS ANCHORED OVER THE WESTERN CARIBBEAN SEA. WITH THE UPPER LEVEL TROUGHING CONTINUING TO SLIDE E-SE INTO NORTHERN PORTIONS OF THE SW NORTH ATLC...A DISSIPATING COLD FRONT IS ANALYZED AT 18/0300 UTC FROM THE SOUTHERN FLORIDA PENINSULA NEAR 26N81W TO 26N90W AND BECOMES STATIONARY ALONG 26N95W TO 22N96W TO 21N97W THEN INLAND OVER EAST-CENTRAL INTERIOR MEXICO. LOW-LEVEL MOISTURE REMAINS LIMITED ALONG THE COLD FRONT...HOWEVER...ISOLATED SHOWERS ARE POSSIBLE THROUGH THE OVERNIGHT HOURS WITHIN 90 NM EITHER SIDE OF THE STATIONARY FRONT. THE FRONT IS EXPECTED TO CONTINUE DISSIPATING AS SURFACE HIGH PRESSURE CURRENTLY ANCHORED AS A 1031 MB HIGH CENTERED OVER NORTH TEXAS BUILDS EASTWARD ACROSS THE SE CONUS THROUGH LATE SUNDAY AND PROVIDES MOSTLY EAST TO NORTHEAST WINDS ACROSS MUCH OF THE GULF. BY MONDAY...SOUTHERLY RETURN FLOW IS EXPECTED TO RE-ESTABLISH OVER PORTIONS OF THE WESTERN GULF AS AN AREA OF LOW PRESSURE DEVELOPS OVER NORTH TEXAS AND OKLAHOMA. THE NEXT COLD FRONT IS THEN FORECAST TO ENTER THE NW GULF WATERS EARLY TUESDAY. CARIBBEAN SEA... AN UPPER LEVEL ANTICYCLONIC CIRCULATION INFLUENCES MUCH OF THE WESTERN CARIBBEAN CENTERED NEAR 16N76W WITH AXIS EXTENDING NW TO NEAR 22N85W. ON THE WESTERN PERIPHERY OF THE RIDGE...SOUTHERLY DIFFLUENT FLOW ALOFT CONTINUES TO ENHANCE SCATTERED SHOWERS AND ISOLATED TSTMS S OF 17N BETWEEN 78W-85W...INCLUDING PORTIONS OF PANAMA...COSTA RICA...AND EASTERN NICARAGUA. MOST OF THIS CONVECTIVE ACTIVITY IS FOCUSED IN THE VICINITY AND NORTH OF THE MONSOON TROUGH AXIS EXTENDING FROM THE E PACIFIC ALONG 10N TO NORTHERN COLOMBIA. OTHERWISE THE REMAINDER OF THE WESTERN CARIBBEAN W OF 70W IS UNDER STRONG NE TRADES DUE TO AN INCREASED PRESSURE GRADIENT FROM A HIGH PRESSURE CENTER OVER THE SW NORTH ATLC. FARTHER EAST...A VERY DRY AND STABLE ATMOSPHERE IS NOTED UNDER NW FLOW ALOFT ON THE EASTERN PERIPHERY OF THE PREVIOUSLY MENTIONED UPPER LEVEL RIDGE. NE TRADES PREVAIL E OF 70W AS WELL...HOWEVER REMAIN GENERALLY FROM 10 TO 15 KT. TWO AREAS OF ISOLATED SHOWERS ARE ALSO NOTED ON SATELLITE IMAGERY...ONE N OF 16N E OF 70W...AND THE OTHER S OF 14N E OF 70W. HIGH PRESSURE IS FORECAST TO REMAIN ANCHORED NE OF THE BAHAMAS THROUGH LATE SUNDAY MAINTAINING THE AREA OF INCREASED E-NE TRADES. ATLANTIC OCEAN... AN UPPER LEVEL LONGWAVE TROUGH IS PROGRESSING OVER THE EASTERN CONUS AND SUPPORTS A COLD FRONT ANALYZED INTO THE DISCUSSION AREA NEAR 32N73W THAT EXTENDS SW TO THE SOUTHERN FLORIDA PENINSULA NEAR 27N80W. POSSIBLE ISOLATED SHOWERS ARE OCCURRING WITHIN 90 NM EITHER SIDE OF THE FRONT. TO THE SE OF THE COLD FRONT...AN UPPER LEVEL RIDGE AXIS EXTENDS FROM THE WESTERN CARIBBEAN SEA ALONG 20N74W TO BEYOND 32N62W AND SUPPORTS A WEAKENING 1021 MB SURFACE HIGH CENTERED NEAR 27N69W. MOSTLY NE WINDS ARE NOTED WITHIN THE SOUTHEASTERN PERIPHERY OF THE HIGH AS A RECENT ASCAT PASS AROUND 18/0052 UTC DEPICTED WINDS IN THE RANGE OF 10 TO 15 KT. OVER THE CENTRAL ATLC...AN UPPER LEVEL LOW IS CENTERED NEAR 27N50W AND EXTENDS TROUGHING SOUTHWARD TO 08N BETWEEN 43W-64W. THE UPPER LEVEL LOW SUPPORTS A COLLOCATED SURFACE LOW WITH A SET OF FRONTAL BOUNDARIES ASSOCIATED WITH THE SYSTEM. A STATIONARY FRONT EXTENDS FROM NE OF THE LOW CENTER ALONG 29N47W TO 24N45W TO 17N48W THEN AS SURFACE TROUGH TO 12N50W. SCATTERED SHOWERS AND TSTMS ARE OCCURRING WITHIN 240 NM EAST OF THE BOUNDARY N OF 17N. CLOSER TO THE LOW CENTER...A SECONDARY COLD FRONT IS ANALYZED FROM 26N50W TO 24N48W TO 20N53W. SCATTERED SHOWERS ARE OCCURRING FROM 25N-29N BETWEEN 47W-50W. BOTH OF THESE CONVECTIVELY ACTIVE AREAS ARE ENHANCED EAST OF THE UPPER LEVEL TROUGH AXIS DUE TO STRONG UPPER LEVEL DIFFLUENCE. THE REMAINDER OF THE EASTERN ATLC IS UNDER THE INFLUENCE OF A SURFACE RIDGE ANCHORED BY A 1034 MB HIGH CENTERED SE OF THE AZORES NEAR 36N24W. THE RIDGE AXIS EXTENDS SW FROM THE HIGH TO 15N32W. FOR ADDITIONAL INFORMATION PLEASE VISIT HTTP://WWW.HURRICANES.GOV/MARINE $$ HUFFMAN