000 AXNT20 KNHC 142357 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 705 PM EST SUN DEC 14 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 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 2315 UTC. ...THE ITCZ... ITCZ IS CENTERED ALONG 7N11W 4N20W 4N35W 4N53W. SCATTERED MODERATE TO STRONG CONVECTION IS WITHIN 60-80 NM S OF THE AXIS BETWEEN 22W-33W...AND WITHIN 45 NM N OF THE AXIS BETWEEN 33W-37W. SCATTERED MODERATE CONVECTION IS ALSO NOTED FROM 5N-11N BETWEEN 38W-52W LIKELY ASSOCIATED WITH A SFC TROUGH EMBEDDED WITHIN THE ITCZ. ...DISCUSSION... GULF OF MEXICO... AN UPPER-LEVEL RIDGE CENTERED ON A HIGH OVER THE NW CARIBBEAN DOMINATES THE ENTIRE GULF. STRONG W TO NW MID-UPPER FLOW...ON THE N PERIPHERY OF THIS RIDGE...IS SPREADING CONSIDERABLE PACIFIC MOISTURE ACROSS NORTHERN MEXICO AND THE GULF REGION N OF 25N. CONVECTIVE CLOUDS STREETS ARE FORMING PARALLEL TO THE SLY RETURN FLOW PARTICULARLY OVER THE WESTERN HALF OF THE GULF. DRIER AIR IS PRESENT S OF 25N CLOSER TO THE UPPER RIDGE AXIS. AT THE SURFACE...STRONG HIGH PRES OVER THE W ATLC IS MAINTAINING STRONG E TO SE WINDS OVER THE E GULF AND SE TO S WINDS OVER THE REMAINDER OF THE AREA. AN EARLIER ASCAT PASS SHOWED SLY WINDS OF 25 KT WEST OF 95W. THESE WINDS WILL BECOME MORE UNIFORM S TO SE TONIGHT AND MON AS THE NEXT COLD FRONT APPROACHES THE TEXAS COAST MON AFTERNOON...INCREASING THE CHANCE OF SHOWERS OVER THE NW PORTION OF THE GULF. THE FRONT IS FORECAST TO MOVE OFF THE TEXAS COAST MON NIGHT AND STALL IN THE COASTAL WATERS EARLY TUE BEFORE GRADUALLY MOVING BACK INLAND AROUND MID WEEK. CARIBBEAN SEA... AN UPPER-LEVEL HIGH CENTERED OVER THE GULF OF HONDURAS IS PRODUCING N TO NW FLOW OVER THE CENTRAL AND EASTERN CARIBBEAN AND ABUNDANT DRY SINKING AIR OVER MUCH OF THE AREA. A FEW PATCHES OF LOW LEVEL MOISTURE ARE SEEN ACROSS THE REGION MORE CONCENTRATED NEAR THE ABC ISLANDS WHERE A WEAK SFC TROUGH IS ANALYZED. THE TROUGH LIES ALONG 66W/67W SOUTH OF 15N. SCATTERED SHOWERS ARE NEAR THE COAST OF COSTA RICA AND NICARAGUA LIKELY PRODUCED BY LOW-LEVEL WIND SPEED CONVERGENCE AND A DIFFLUENT PATTERN ALOFT NEAR THE AFOREMENTIONED UPPER-LEVEL HIGH. FRAGMENTS OF MOISTURE ARE ALSO MOVING FROM THE ATLC ACROSS E AND CENTRAL CUBA UNDER AN E-NE WIND FLOW AROUND THE PERIPHERY OF THE STRONG HIGH PRES SITUATED OVER THE W ATLC NEAR 39N67W. PRES GRADIENT BETWEEN THIS HIGH AND RELATIVE LOW PRES OVER THE CARIBBEAN IS RESULTING IN FRESH TRADE WINDS ACROSS THE BASIN. ATLANTIC OCEAN... AN UPPER-LEVEL TROUGH OVER THE CENTRAL ATLC MAINLY N OF 30N SUPPORTS A COLD FRONT THAT ENTERS THE FORECAST AREA NEAR 31N53W THEN CONTINUES SW TO NEAR 24N68W. AT THIS POINT...IT BECOMES STATIONARY EXTENDING OVER THE SE BAHAMAS AND THE WINDWARD PASSAGE. A 1038 MB SFC HIGH LOCATED NEAR 39N67W FOLLOWS THE FRONT. THIS HIGH ENVELOPS THE EASTERN SEABOARD...CUBA AND THE BAHAMAS. THE TIGHT PRES GRADIENT BETWEEN THIS SFC HIGH AND THE FRONT IS PRODUCING A LARGE AREA OF 20-30 KT NE WINDS W OF THE FRONT. AS WAS ADVERTISED BY MUCH OF THE COMPUTER MODELS...A SFC LOW IS BEGINNING TO FORM OVER THE CENTRAL ATLC NEAR 28N54W. THE CLOUD PATTERN IS EXHIBITING SOME CYCLONIC CIRCULATION WITH SCATTERED SHOWERS AROUND THE LOW CENTER. THIS SYSTEM WILL DRIFT SW DURING THE NEXT 24 HOURS AND THEN W TO WSW FOR SEVERAL DAYS. THE PRES GRADIENT IS EXPECTED TO INCREASE BETWEEN THIS DEVELOPING LOW AND THE SFC HIGH CURRENTLY OVER THE W ATLC WITH WINDS REACHING GALE FORCE ON THE WESTERN SIDE OF THE SFC LOW. AN UPPER-LEVEL TROUGH RUNNING FROM 29N56W TO 19N44W IS GENERATING A LARGE AREA OF SCATTERED SHOWERS AND ISOLATED TSTMS N OF 20N BETWEEN 40W-50W. THE SFC PRES PATTERN IS ALSO VERY TIGHT BETWEEN THE DEVELOPING CYCLONE OVER THE CENTRAL ATLC AND A 1035 MB HIGH JUST W OF THE AZORES. AS A RESULT...SCATTEROMETER DATA INDICATE A SWATH OF 20-30 KT E TO SE WINDS ACROSS THE E ATLC PARTICULARLY FROM 15N-24N AND EST OF 40W. MAINLY WESTERLY ZONAL FLOW ALOFT DOMINATES THE DEEP TROPICS...WITH UPPER LEVEL DIFFLUENCE ENHANCING CONVECTION WITHIN THE ITCZ. $$ GR