000 AXNT20 KNHC 182341 TWDAT TROPICAL WEATHER DISCUSSION NWS NATIONAL HURRICANE CENTER MIAMI FL 705 PM EST TUE DEC 18 2012 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 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 2315 UTC. ...ITCZ/MONSOON TROUGH... THE MONSOON TROUGH EXTENDS FROM THE AFRICAN COAST NEAR 07N11W TO 06N14W. THE INTERTROPICAL CONVERGENCE ZONE AXIS EXTENDS FROM 06N14W TO 04N21W TO 05N37W TO 04N43W. WIDELY SCATTERED MODERATE CONVECTION IS FROM THE EQUATOR TO 07N BETWEEN 10W-40W...AND FROM THE EQUATOR TO 09N BETWEEN 40W-51W. ...DISCUSSION... GULF OF MEXICO... WATER VAPOR IMAGERY INDICATES A VIGOROUS MID-LEVEL SHORTWAVE TROUGH IS PROGRESSING EASTWARD OFF THE CAROLINA COAST THIS EVENING IN THE VICINITY OF 33N76W. THIS FEATURE SUPPORTS A COLD FRONT THAT AS OF 18/2100 UTC IS ANALYZED FROM MELBOURNE TO SARASOTA FLORIDA AND INTO THE GULF W-SW TO 25N90W. THE FRONT REMAINS PRECIPITATION-FREE ACROSS THE GULF WATERS THIS EVENING...HOWEVER THE MAIN IMPACT WITH THE FRONT IS THE NOTICEABLE DIFFERENCE IN AIRMASS CONTRAST WITH DEWPOINTS NORTH OF THE FRONT CONSIDERABLY DRIER THAN THOSE ACROSS THE SOUTHERN FLORIDA PENINSULA AND PORTIONS OF THE SE GULF. MOSTLY DRY CONDITIONS ARE NOTED ON WATER VAPOR IMAGERY THIS EVENING OVER THE REMAINDER OF THE BASIN AS WEAK HIGH PRESSURE CONTINUES TO DOMINATE. A 1017 MB HIGH IS CENTERED NEAR 30N87W AND IS EXPECTED TO SLOWLY SHIFT EASTWARD AND INTO THE SW NORTH ATLC BY LATE WEDNESDAY. AS THIS OCCURS...WINDS WILL VEER AND BECOME MORE SOUTHERLY THROUGH EARLY THURSDAY AS A STRONG LOW PRESSURE AREA DEVELOPS OVER THE CENTRAL PLAINS AND MID-MISSISSIPPI RIVER VALLEY. THE NEXT COLD FRONT IS FORECAST TO EMERGE OFF THE TEXAS AND LOUISIANA COAST THURSDAY MORNING. CARIBBEAN SEA... CONDITIONS ACROSS THE CARIBBEAN SEA BASIN REMAIN FAIRLY TRANQUIL THIS EVENING AS WATER VAPOR IMAGERY INDICATES VERY DRY AIR AND SUBSIDENCE PREVAILS ALOFT. AN UPPER LEVEL ANTICYCLONIC CIRCULATION IS CENTERED NEAR 20N66W AND INFLUENCES MUCH OF THE NE CARIBBEAN WHILE AN UPPER LEVEL TROUGH IS CENTERED OVER THE SW CARIBBEAN NEAR 13N77W. AT THE SURFACE...A FAIRLY WEAK PRESSURE GRADIENT IS IN PLACE ACROSS THE CARIBBEAN WITH TRADES REMAINING IN THE RANGE OF 10 TO 20 KT THROUGH THE OVERNIGHT PERIOD INTO WEDNESDAY. POSSIBLE ISOLATED LOW-TOPPED SHOWERS ARE OCCURRING OVER THE NW CARIBBEAN AND PORTIONS OF CENTRAL AMERICA FROM 11N-22N BETWEEN 80W-87W AND OVER THE EASTERN CARIBBEAN E OF 70W. THE TRADE WINDS ARE FORECAST TO INCREASE GRADUALLY BETWEEN 70W-80W THURSDAY INTO FRIDAY WEAKEN AGAIN THEREAFTER AS A COLD FRONT WILL MOVE INTO THE NW CARIBBEAN LATE FRIDAY INTO SATURDAY. ATLANTIC OCEAN... A MID-LEVEL SHORTWAVE TROUGH IS CENTERED OFFSHORE OF THE CAROLINAS NEAR 33N76W THAT SUPPORTS A COLD FRONT ANALYZED FROM 32N76W TO MELBOURNE FLORIDA NEAR 28N81W. THE FRONT REMAINS FREE OF PRECIPITATION THIS EVENING...HOWEVER TO THE EAST OF THE FRONT IN THE AREA OF MAXIMUM MIDDLE TO UPPER LEVEL DIFFLUENCE...WIDELY SCATTERED SHOWERS AND ISOLATED TSTMS ARE OCCURRING N OF 30N BETWEEN 50W AND THE FRONT. THIS AREA CONTINUES TO RESIDE IN THE WARM SECTOR OF A COMPLEX AREA OF LOW PRESSURE CENTERED OFF THE NEW ENGLAND COAST IN THE WESTERN NORTH ATLC. OTHERWISE...THE REMAINDER OF THE SW NORTH ATLC IS UNDER THE INFLUENCE OF A SURFACE RIDGE ANCHORED BY A 1020 MB HIGH CENTERED IN THE CENTRAL ATLC NEAR 32N46W. THE RIDGE AXIS EXTENDS FROM THE HIGH SW TO THE SE BAHAMAS NEAR 22N73W. MOSTLY FAIR CONDITIONS ARE NOTED ON SATELLITE IMAGERY THIS EVENING WITH ONLY A FEW ISOLATED LOW- TOPPED SHOWERS OCCURRING FROM 21N-28N BETWEEN 69W-74W. FINALLY...AN UPPER LEVEL TROUGH IS OVER THE EASTERN ATLC WITH AXIS EXTENDING FROM 28N37W TO A BASE NEAR 16N50W. THIS TROUGHING SUPPORTS A COLD FRONT ANALYZED INTO THE DISCUSSION AREA NEAR 32N29W THAT EXTENDS SW TO 24N43W. A WEAK PRE-FRONTAL SURFACE TROUGH IS FROM 25N40W TO 20N45W. ISOLATED SHOWERS AND TSTMS ARE OCCURRING WITHIN 75 NM EITHER SIDE OF THE FRONT. FOR ADDITIONAL INFORMATION PLEASE VISIT HTTP://WWW.HURRICANES.GOV/MARINE $$ HUFFMAN