000 AXNT20 KNHC 101749 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 105 PM EST WED DEC 10 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... THE ITCZ IS CENTERED ALONG 6N9W 4N23W 7N34W 9N46W 6N58W. A SURFACE TROUGH IS EMBEDDED WITHIN THE ITCZ. THIS SURFACE TROUGH EXTENDS FROM 14N53W TO 11N54W TO 8N54W. LOW LEVEL CONVERGENCE IS SUPPORTING SCATTERED MODERATE CONVECTION WITHIN 300 NM E AND 90 NM W OF THIS SURFACE TROUGH. ELSEWHERE...SCATTERED MODERATE CONVECTION IS FROM 4N-10N BETWEEN 13W-26W. SCATTERED MODERATE CONVECTION IS ALSO FROM 7N-9N BETWEEN 44W-47W. ...DISCUSSION... GULF OF MEXICO... A MAJOR CHANGE IN THE WEATHER PATTERN IS ONGOING ACROSS PORTIONS OF THE GULF REGION...AS A VIGOROUS AND DEEP TROUGH OVER THE CENTRAL CONUS AND N MEXICO ADVANCES EASTWARD. AN ASSOCIATED SURFACE COLD FRONT OVER THE W GULF EXTENDS FROM S MISSISSIPPI NEAR 30N89W TO 26N93W TO THE E COAST OF MEXICO NEAR 21N97W...AND EXTENDS FARTHER TO THE WEST AND NORTHWEST OVER MEXICO. THIS FRONT IS MOVING EASTWARD. AHEAD OF THE COLD FRONT...S TO SE SURFACE WINDS OF 20 TO 30 KT CONTINUE TO ADVECT LOW LEVEL MOISTURE ACROSS PORTIONS OF THE E AND CENTRAL GULF...WHERE INSTABILITY CONTINUES TO INCREASE. THIS INCREASING INSTABILITY...COMBINED WITH WITH STRONG LOW LEVEL CONVERGENCE IN THE VICINITY OF THE COLD FRONT...IS SUPPORTING NUMEROUS STRONG TO SEVERE THUNDERSTORMS ALONG AND WITHIN 120 NM E OF THE COLD FRONT N OF 26N WITH A SQUALL LINE EXTENDING FROM 29N90W TO THE W FLORIDA PANHANDLE NEAR 31N87W. AS THE AFOREMENTIONED DEEP TROUGH CONTINUES TO APPROACH THE GULF...STRONG ATMOSPHERIC LIFT ASSOCIATED WITH A 110 TO 120 KT UPPER LEVEL JET MAXIMUM OVER THE THE NW GULF IS SUPPORTING THIS SHOWER AND THUNDERSTORM ACTIVITY...ALONG WITH THE PRESENCE OF STRONG VERTICAL WIND SHEAR. IN FACT...THE STORM PREDICTION CENTER IN NORMAN OKLAHOMA HAS ISSUED A TORNADO WATCH FOR PORTIONS OF SOUTHERN AND EASTERN ALABAMA...THE WESTERN AND CENTRAL FLORIDA PANHANDLE...AS WELL AS THE ADJACENT COASTAL WATERS...EFFECTIVE UNTIL 300 PM EST THIS AFTERNOON. OVER THE SW GULF...A 1007 MB SURFACE LOW IN THE BAY OF CAMPECHE IS NEAR 20N41W...WITH AN ATTENDANT SURFACE TROUGH EXTENDING FROM THE SURFACE LOW TO 23N93W TO 26N93W WHERE THE SURFACE TROUGH INTERSECTS THE AFOREMENTIONED COLD FRONT. LOW LEVEL CONVERGENCE IS SUPPORTING SCATTERED SHOWERS WITHIN 60 NM EITHER SIDE OF THE SURFACE TROUGH N OF 22N. OVER THE NEXT DAY...THE AFOREMENTIONED SURFACE COLD FRONT IS FORECAST TO CONTINUE MOVING EASTWARD ACROSS THE GULF REGION...WITH CONTINUING CHANCES OF STRONG TO SEVERE THUNDERSTORMS ALONG AND AHEAD OF THE COLD FRONT. IN THE WAKE OF THE COLD FRONT... INCREASED NW TO N SURFACE WINDS ARE PRESENT WITH A STRONG SURFACE PRESSURE GRADIENT...WITH GALE CONDITIONS OCCURRING ACROSS THE NW GULF...AND STORM CONDITIONS DEVELOPING DURING THE NEXT DAY ACROSS THE SW GULF. ALSO...A RELATIVELY COOLER AIRMASS IS PRESENT IN THE WAKE OF THE COLD FRONT...WITH SURFACE TEMPERATURES IN THE UPPER 30S AND LOWER 40S ACROSS PORTIONS OF SE TEXAS AND SW LOUISIANA. THIS RELATIVELY COOLER AIRMASS IS BEING SUPPORTED BY A 1032 MB SURFACE HIGH IN W TEXAS NEAR 32N104W. ADDITIONALLY...STRONG NW TO N SURFACE WINDS ARE FORECAST TO BLOW THROUGH THE ISTHMUS OF TEHUANTEPEC RESULTING IN GALE FORCE WINDS IN THE E PACIFIC REGION BEGINNING AT 11/0600 UTC. CARIBBEAN SEA... BROAD ANTICYCLONIC FLOW ALOFT...AROUND AN UPPER HIGH OVER N VENEZUELA NEAR 8N70W...IS PRESENT ACROSS THE CARIBBEAN REGION. MID/UPPER-LEVEL MOISTURE CONTINUES STREAMING ACROSS THE W GULF IN SOUTHWESTERLY AND WESTERLY FLOW ALOFT W AND N OF THE UPPER HIGH. SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS ARE OCCURRING OVER THE SW CARIBBEAN S OF 11N W OF 75W...WHICH ARE BEING SUPPORTED BY LOW LEVEL CONVERGENCE IN THE VICINITY OF A 1009 MB SURFACE LOW IN N COLOMBIA NEAR 11N75W...AS WELL AS UPPER LEVEL DIVERGENCE TO THE W OF UPPER HIGH OVER N VENEZUELA. OVER THE SE CARIBBEAN...DEEP LAYER DRY AIR IS INHIBITING DEEP CONVECTION. ACROSS THE CARIBBEAN...GENERALLY NE TO E SURFACE WINDS OF 20 TO 25 KT PREVAIL. DURING THE NEXT DAY...THE COLD FRONT OVER THE GULF OF MEXICO WILL CONTINUE TO APPROACH THE NW GULF...WITH A RELATIVELY COOLER AIRMASS IN THE WAKE OF THE COLD FRONT. ATLANTIC OCEAN... MOIST SOUTHWESTERLY FLOW ALOFT CONTINUES TO INCREASE OVER THE W ATLC AS THE AFOREMENTIONED DEEP TROUGH OVER THE CENTRAL CONUS AND N MEXICO CONTINUES PROGRESSING EASTWARD. DURING THE NEXT DAY...THE COLD FRONT OVER THE GULF OF MEXICO WILL CONTINUE TO APPROACH THE W ATLC. FARTHER TO THE E...A SURFACE STATIONARY FRONT EXTENDS FROM 29N59W TO 30N45W TO 32N41W...WITH LOW LEVEL CONVERGENCE SUPPORTING SCATTERED SHOWERS WITHIN 90 NM EITHER SIDE OF THE STATIONARY FRONT E OF 50W. N OF THIS STATIONARY FRONT...SUBSIDENCE AROUND A 1044 MB SURFACE HIGH NEAR 41N46W IS GENERALLY SUPPORTING FAIR WEATHER. ALSO...ATMOSPHERIC LIFT AND INSTABILITY IN THE VICINITY OF AN UPPER TROUGH N OF 24N BETWEEN 24W-34W ARE SUPPORTING SCATTERED SHOWERS FROM 24N-29N BETWEEN 24W-32W. ACROSS THE TROPICAL ATLC...GENERALLY WESTERLY FLOW ALOFT IS PRESENT. ALSO...A SURFACE TROUGH EMBEDDED WITHIN THE ITCZ EXTENDS FROM 14N53W TO 11N54W TO 8N54W...WITH SCATTERED MODERATE CONVECTION WITHIN 300 NM E AND 90 NM W OF THIS SURFACE TROUGH. $$ COHEN