000 AXNT20 KNHC 201742 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 105 PM EST SAT DEC 20 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 5N10W 6N31W 7N40W 9N49W 6N58W. A PAIR OF SFC TROUGHS ARE EMBEDDED WITHIN THE ITCZ. FROM E TO W...THE FIRST ONE IS ALONG 32W/33W SOUTH OF 11N. THE SECOND ONE IS ALONG 50W SOUTH OF 15N. SCATTERED MODERATE CONVECTION IS NOTED EITHER SIDE OF BOTH TROUGHS. IN ADDITION...VIS SATELLITE IMAGERY SHOWS A WEAK LOW WITHIN THE ITCZ AXIS NEAR 6N37W WHERE IS GENERATING SOME SHOWER ACTIVITY. ELSEWHERE...SCATTERED MODERATE CONVECTION IS WITHIN 120 NM N OF AXIS BETWEEN 18W-23W...AND NEAR 2N12W. ...DISCUSSION... GULF OF MEXICO... AS OF 1500 UTC...A 1022 MB SURFACE HIGH CENTERED OVER CENTRAL FLORIDA EXTENDS A RIDGE OVER THE SE CONUS AND MOST OF THE GULF REGION. ALOFT...BROAD ANTICYCLONIC FLOW ASSOCIATED WITH AN UPPER LEVEL HIGH LOCATED NEAR TAMPICO MEXICO DOMINATES THE ENTIRE GULF INCLUDING ALSO SOUTH-CENTRAL MEXICO. STRONG UPPER LEVEL SUBSIDENCE AND IMPLIED DRY AIR MASS ASSOCIATED WITH THIS HIGH IS RESULTING IN ATMOSPHERIC STABILITY AND FAIR WEATHER CONDITIONS ACROSS MUCH OF THE GULF REGION. THE DRIEST AIR ALOFT IS OVER THE ISTHMUS OF TEHUANTEPEC. FARTHER TO THE N...A DEEP LONGWAVE TROUGH WITH AN ASSOCIATED STRONG UPPER LEVEL JET MAXIMUM OVER THE CENTRAL CONUS IS SUPPORTING A FRONTAL SYSTEM FORECAST TO MOVE OFF THE TEXAS COAST EARLY SUN MORNING FOLLOWED BY STRONG N-NE WINDS. THESE WINDS ARE EXPECTED TO REACH GALE FORCE OVER THE NW GULF SUN AFTERNOON AND EVENING. A GALE WARNING IS ALREADY IN EFFECT FOR THE NW GULF BEGINNING 21/1800 UTC. ACCORDING WITH THE GFS COMPUTER MODEL...A SFC LOW PRES IS FORECAST TO DEVELOP OVER THE WESTERN GULF MON EVENING AS THE FRONT DIPS SOUTHWARD THROUGH THE NORTHERN YUCATAN PENINSULA. CARIBBEAN SEA... THE CARIBBEAN SEA IS PRETTY QUIET TODAY UNDER THE INFLUENCE OF A BROAD RIDGE ALOFT WHICH IS PRODUCING STRONG SUBSIDENCE ACROSS THE BASIN. THIS UPPER-LEVEL RIDGE ALSO ENVELOPS CENTRAL AMERICA AND THE N PORTION OF COLOMBIA AND VENEZUELA. AS A RESULT...ONLY FRAGMENTS OF LOW LEVEL CLOUDS WITH EMBEDDED LIGHT SHOWERS ARE NOTED ACROSS THE REGION USHERED IN ON A NE WIND FLOW. VIS SATELLITE IMAGERY ALSO REVEALS A WELL DEFINED SWIRL OF LOW LEVEL CLOUDS SW OF PUERTO RICO. THIS LOW LEVEL FEATURE IS EMBEDDED IN A SFC TROUGH WHICH RUNS FROM 28N59W TO 23N62W TO PUERTO RICO. THE SAN JUAN DOPPLER RADAR DEPICTS ISOLATED SHOWERS ASSOCIATED WITH TROUGH. SFC HIGH PRES N OF AREA IS BRINGING NE SURFACE WINDS OF 10 TO 20 KT TO THE CARIBBEAN REGION...EXCEPT UP TO 25 KT NEAR THE COAST OF COLOMBIA. LOOKING AHEAD...WINDS ARE EXPECTED TO INCREASE EARLY NEXT WEEK ACROSS THE CARIBBEAN SEA AS HIGH PRES BUILDS TO THE NORTH. ATLANTIC OCEAN... AS OF 1500 UTC...A 1022 MB SURFACE HIGH SITUATED OVER CENTRAL FLORIDA DOMINATES THE W ATLC PRODUCING MOSTLY FAIR CONDITIONS. BROKEN TO OVERCAST STRATOCUMULUS CLOUDS ARE NOTED OVER THE NW BAHAMAS AND SE FLORIDA. FURTHER E...A SFC TROUGH IS ANALYZED FROM 28N59W TO 23N62W TO PUERTO RICO. ANOTHER SWIRL OF LOW CLOUDS IS NEAR THE N END OF THIS TROUGH. ANOTHER SFC TROUGH IS ANALYZED ALONG 47W FROM 22N-29N. THIS TROUGH IS LIKELY A REFLECTION OF AN UPPER-LEVEL TROUGH WHICH EXTENDS ACROSS THE CENTRAL ATLC FROM 31N44 W TO THE N LEEWARD ISLANDS. UPPER DIFFLUENCE AHEAD OF THIS TROUGH IS SUPPORTING SCATTERED MODERATE CONVECTION BETWEEN THE ABOVE MENTIONED SFC TROUGH ALONG 50W AND THE WINDWARD ISLANDS. IN FACT...BARBADOS REPORTED THIS MORNING 3.08 INCHES OF RAIN FOR THE PAST 24 HOURS. ANOTHER AREA OF CLOUDINESS WITH EMBEDDED SHOWERS IS WITHIN 450 NM AHEAD OF THE SFC TROUGH LOCATED ALONG 47W. THIS ACTIVITY IS BEING ENHANCED BY A DIFFLUENT PATTERN ALOFT. THE REMAINDER OF THE ATLC FORECAST REGION IS DOMINATING BY A RIDGE ANCHORED ON A HIGH WELL N OF THE AREA. IN THE UPPER LEVELS...A RIDGE/TROUGH/RIDGE/TROUGH PATTERN COVERS THE ENTIRE REGION. $$ GR