000 AXNT20 KNHC 211740 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 105 PM EST SUN DEC 21 2008 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...METEOROLOGICAL ANALYSIS...WEATHER OBSERVATIONS...AND RADAR. BASED ON 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 1715 UTC. ...THE ITCZ... ITCZ IS CENTERED ALONG 6N9W 5N10W 4N20W 8N33W 6N45W INTO THE GUYANAS. A PAIR OF SURFACE TROUGHS ARE EMBEDDED WITHIN THE ITCZ. ONE IS ALONG 35W/36W S OF 14N AND THE OTHER IS ALONG 50W/51W S OF 14N. A CLUSTER OF MODERATE CONVECTION IS NEAR THE N END OF THE FIRST TROUGH. ELSEWHERE...SCATTERED MODERATE CONVECTION IS S OF 4N BETWEEN 8W-15W. SCATTERED MODERATE CONVECTION IS FROM EQUATOR TO 7N BETWEEN 20W-31W...AND WITHIN 220 NM SOUTH OF AXIS BETWEEN 10W-20W. ...DISCUSSION... GULF OF MEXICO... TODAY MARKS THE FIRST DAY OF WINTER IN THE NORTHERN HEMISPHERE. IN THIS DAY...TWO MAJOR WINTER STORMS ARE IMPACTING THE CONUS... ONE THE PACIFIC NW AND THE OTHER THE NE. A COLD FRONT EXTENDS FROM THIS SECOND WINTER STORM ACROSS THE SE U.S. ENTERING THE GULF OF MEXICO THROUGH SE LOUISIANA THEN CONTINUING SW TO THE DEEP SOUTH TEXAS AND N MEXICO. SCATTERED SHOWERS ARE ALONG AND WITHIN 60 NM AHEAD OF THE FRONT. THE FRONT WILL MOVE SE ACROSS THE GULF WATERS REACHING FROM SOUTH FLORIDA TO NEAR TAMPICO MEXICO LATE TONIGHT. WINDS ARE EXPECTED TO INCREASE TO GALE FORCE TONIGHT AND EARLY MON OVER THE NW GULF N OF FRONT. A GALE WARNING IS ALREADY IN EFFECT BEGINNING 22/0000 UTC. RELATIVELY COOLER AND DRIER CONDITIONS ARE PRESENT IN THE WAKE OF THE COLD FRONT. AS OF 1500 UTC...A 1019 MB SURFACE HIGH CENTERED OVER THE NW BAHAMAS NEAR 26N78W EXTENDS A RIDGE ACROSS SOUTH-CENTRAL FLORIDA INTO THE EASTERN HALF OF THE GULF AND THE YUCATAN PENINSULA. ALOFT...BROAD ANTICYCLONIC FLOW ASSOCIATED WITH AN UPPER LEVEL RIDGE EXTENDING FROM THE WRN CARIBBEAN TO ACROSS CUBA AND THE FLORIDA PENINSULA DOMINATES MUCH OF THE GULF...THE YUCATAN PENINSULA AND SRN MEXICO PRODUCING ATMOSPHERIC STABILITY AND MOSTLY FAIR WEATHER CONDITIONS ACROSS THE REGION. FARTHER TO THE N...A DEEP LAYERED TROUGH IS OVER THE EASTERN CONUS DIGGING INTO THE FAR N GULF WATERS. THIS UPPER-LEVEL TROUGH SUPPORTS THE AFOREMENTIONED COLD FRONT. CARIBBEAN SEA... THE CARIBBEAN SEA REMAINS UNDER THE INFLUENCE OF A BROAD RIDGE ALOFT WHICH IS PRODUCING STRONG SUBSIDENCE ACROSS THE ENTIRE BASIN. THIS UPPER-LEVEL RIDGE ALSO ENVELOPS CENTRAL AMERICA AND THE NORTHERN PORTION OF COLOMBIA AND VENEZUELA. AS A RESULT... POCKETS OF LOW LEVEL CLOUDS WITH EMBEDDED LIGHT SHOWERS ARE NOTED ACROSS THE REGION USHERED IN ON E-NE WINDS. THE LARGEST CLUSTERS ARE AFFECTING CENTRAL AMERICA...PARTICULARLY FROM COSTA RICA TO HONDURAS. SIMILAR CLOUDINESS IS SEEN OVER PARTS OF BELIZE AND NEAR NOAA BUOY 42058 OVER THE CENTRAL CARIBBEAN. LOOKING AHEAD...THE COLD FRONT CURRENTLY MOVING ACROSS THE GULF OF MEXICO WILL ENTER THE YUCATAN CHANNEL AND WESTERN CUBA MONDAY MORNING. WINDS ARE EXPECTED TO INCREASE EARLY NEXT WEEK ACROSS THE CARIBBEAN SEA AS HIGH PRES BUILDS TO THE NORTH. ATLANTIC OCEAN... A WEAKENING SFC RIDGE WITH THREE 1019 MB CENTERS DOMINATES THE W AND CENTRAL ATLC W OF 50W PRODUCING MOSTLY FAIR WEATHER CONDITIONS. THE MAIN HIGH PRES CENTER IS LOCATED NEAR 25N66W. THIS FEATURE WILL CONTINUE TO MOVE EWD AS THE COLD FRONT MENTIONED ABOVE MOVES OFF THE SE U.S. LATE TONIGHT. ONLY FRAGMENTS OF LOW LEVEL CLOUDS ARE NOTED UNDER THE INFLUENCE OF THIS RIDGE. FURTHER E...A SFC TROUGH REMAINS OVER THE CENTRAL ATLC...AND IS ANALYZED FROM 27N44W TO 18N45W. THIS TROUGH IS LIKELY A REFLECTION OF AN UPPER-LEVEL TROUGH WHICH ENTER THE FORECAST AREA NEAR 31N36W THEN CONTINUES SW TO THE WINDWARD ISLANDS. UPPER DIFFLUENCE BETWEEN THIS TROUGH AND A RIDGE ANCHORED ON A HIGH SE OF THE CAPE VERDE ISLANDS NEAR 7N15W IS HELPING TO INDUCE CONVECTION ALONG AND NEAR THE ITCZ AXIS. A JET STREAM BRANCH WITH CORE WINDS OF 70-90 KT IS SE OF THE UPPER TROUGH AND EXTENDS ALONG 17N43W 23N28W ENTERING W AFRICA NEAR 22N17W. SFC HIGH PRES CENTERED WELL N OF AREA COVERS THE E ATLC AND WESTERN AFRICA. NE TO E WINDS ARE EXPECTED TO INCREASE ACROSS THE TROPICS LATE MONDAY TO AT LEAST MIDWEEK AS STRONG HIGH PRES BUILDS N OF AREA. THE GFS COMPUTER MODEL ANTICIPATES A 1038 MB SFC HIGH LOCATED NEAR 36N64W WEDNESDAY MORNING. IN THE UPPER LEVELS...A RIDGE/TROUGH/RIDGE/TROUGH PATTERN COVERS THE ENTIRE REGION WITH A STRONG UPPER-LEVEL LOW JUST N OF THE MADEIRA ISLANDS. $$ GR