000 AXNT20 KNHC 140537 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 105 AM 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 0000 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 0515 UTC. ...THE ITCZ... ITCZ IS CENTERED ALONG 8N13W 4N24W 5N40W 7N50W 6N58W. SCATTERED MODERATE TO STRONG CONVECTION IS WITHIN 120 NM EITHER SIDE OF THE AXIS BETWEEN 22W-34W. SCATTERED MODERATE CONVECTION IS WITHIN 150 NM S OF THE AXIS E OF 14W AND WITHIN 180 NM N OF THE AXIS BETWEEN 46W-49W. ...DISCUSSION... GULF OF MEXICO... STRONG W TO NW MID-UPPER FLOW IS SPREADING WIDESPREAD PACIFIC MOISTURE N OF 24N...BUT EMBEDDED SHOWERS ARE LIKELY ONLY ISOLATED AT MOST W OF 87W AIDED BY MOIST LOW-LEVEL FLOW. DRIER AIR IS PRESENT S OF 24N CLOSER TO AN UPPER RIDGE AXIS OVER CENTRAL AMERICA. IN THE LOWER LEVELS...STRONG HIGH PRES OVER SE VIRGINIA IS PRODUCING STRONG E WINDS OVER THE E GULF AND SE TO S WINDS ELSEWHERE...MODIFYING THE COOL AIRMASS THAT WAS IN PLACE OVER THE PAST COUPLE OF DAYS. THESE WINDS WILL BECOME MORE UNIFORM S TO SE LATER TODAY AND MON AS THE NEXT COLD FRONT APPROACHES THE TEXAS COAST. CARIBBEAN SEA... AN UPPER HIGH CENTERED OVER CENTRAL AMERICA HAS HELPED SET UP ZONAL TO NW FLOW AND ABUNDANT DRY SINKING AIR OVER MUCH OF THE AREA. ONLY AREA OF SIGNIFICANT MOISTURE IS NEAR THE COAST OF COSTA RICA AND NICARAGUA...LIKELY PRODUCED BY LOW-LEVEL SPEED CONVERGENCE (EVIDENT IN QSCAT DATA) AND DIFFLUENCE ALOFT NEAR THE UPPER HIGH CENTER. OTHERWISE...PATCHES OF LOW-LEVEL MOISTURE WITH EMBEDDED SHOWERS ARE SCATTERED ACROSS THE REMAINDER OF THE W CARIBBEAN ASSOCIATED WITH THE REMNANTS OF AN OLD FRONTAL BOUNDARY. LITTLE LARGE SCALE CHANGES ARE EXPECTED OVER THE NEXT COUPLE OF DAYS. ATLANTIC OCEAN... AN UPPER TROUGH ALONG 64W IS FLATTENING SLIGHTLY BUT STILL PROVIDING SUPPORT FOR A COLD FRONT EXTENDING FROM 31N62W TO 22N72W. THE TIGHT PRES GRADIENT BETWEEN THE FRONT AND A 1033 MB HIGH OVER SE VIRGINIA IS PRODUCING A LARGE AREA OF 20-30 KT NE WINDS W OF THE FRONT. UPPER DIFFLUENCE E OF THE UPPER TROUGH AXIS IS PRODUCING A SWATH OF SCATTERED SHOWERS AND TSTMS N OF 25N BETWEEN 59W-62W. FARTHER E...AN UPPER LOW AND A HIGHLY DIFFLUENT UPPER PATTERN IS PRODUCING A LARGE AREA OF SCATTERED SHOWERS AND TSTMS N OF 17N BETWEEN 39W-52W. SHORTWAVE IR IMAGES AND QSCAT DATA REVEALS AN ASSOCIATED SFC TROUGH ALONG 55W N OF 25N...BUT NEARLY ALL OF THE ASSOCIATED WEATHER IS LOCATED IN THE DIFFLUENT ZONE TO ITS E. THE SFC PRES PATTERN IS VERY TIGHT BETWEEN THE TROUGH AND A 1040 MB HIGH JUST W OF THE AZORES PRODUCING 20-30 KT E WINDS ACROSS THE SUBTROPICAL ATLC E OF THE TROUGH AXIS. NWP MODELS CONTINUE TO SUGGEST POSSIBLE LOW PRES DEVELOPMENT OVER THE NEXT FEW DAYS OVER THE CENTRAL ATLC...ASSOCIATED WITH THE COMBINED EFFECTS OF THE DEEP LAYER TROUGHING AND THE TAIL END OF THE WEAKENING FRONT. IN ANTICIPATION OF THE LOW DEVELOPMENT...A GALE WARNING IS POSTED FOR AN AREA NW OF THE LOW...DUE TO THE STRONG GRADIENT BETWEEN IT AND HIGH PRES OVER THE N CENTRAL ATLC. OVER THE FAR TROPICAL E ATLC...AN UPPER JET ALONG 19N/20N IS ADVECTING ABUNDANT MID-HIGH LEVEL MOISTURE TO ITS S E OF 40W AND ENHANCING CONVECTION WITHIN THE ITCZ. $$ CANGIALOSI