000 AXNT20 KNHC 091735 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 105 PM EST TUE DEC 09 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 7N13W 7N30W 6N40W 5N51W. CLUSTERS OF SCATTERED MODERATE CONVECTION ARE FROM 8N-10N BETWEEN 19W-22W... AND FROM 3N-5N BETWEEN 19W-33W. ...DISCUSSION... GULF OF MEXICO... A MAJOR CHANGE IN THE WEATHER PATTERN IS FORECAST FOR THE GULF REGION...AS A VIGOROUS AND DEEP TROUGH OVER THE PLAINS OF THE CONUS ADVANCES EASTWARD. AN ASSOCIATED SURFACE COLD FRONT EXTENDS FROM THE MIDWEST ACROSS THE PLAINS INTO THE SOUTHERN ROCKY MOUNTAIN REGION OF THE CONUS. PRESENTLY...A WARM FRONT IS DRAPED ACROSS THE DEEP SOUTH...EXTENDING FROM A 1003 MB SURFACE LOW IN NE TEXAS NEAR 33N95W ACROSS CENTRAL LOUISIANA...S MISSISSIPPI...AND ALONG THE COAST OF THE FLORIDA PANHANDLE. SOUTH OF THIS WARM FRONT... SE TO S SURFACE WINDS OF 20 TO 25 KT CONTINUE TO DRAW MOIST AND UNSTABLE AIR ACROSS THE GULF REGION. AS THE DEEP TROUGH CONTINUES TO APPROACH THE GULF...STRONG ASCENT ASSOCIATED WITH THE COUPLING OF TWO 100-110 KT UPPER LEVEL JET STREAKS OVER N MEXICO AND TEXAS IS RESULTING IN SCATTERED TO NUMEROUS STRONG TO SEVERE THUNDERSTORMS BREAKING OUT ACROSS TEXAS AND LOUISIANA...AFFECTING NEARBY COASTAL LOCATIONS...WITH ADDITIONAL ISOLATED SHOWERS AND THUNDERSTORMS FARTHER E ACROSS THE GULF N OF 26N BETWEEN 84W-89W. THE PRESENCE OF STRONG VERTICAL WIND SHEAR IS SUPPORTING THE THREAT FOR ORGANIZED SEVERE THUNDERSTORMS OVER PORTIONS OF THE SE CONUS. THIS IS OF PARTICULAR CONCERN OVER PORTIONS OF LOUISIANA AND MISSISSIPPI WHERE STRONG LOW LEVEL VERTICAL WIND SHEAR IS ENHANCED IN THE VICINITY OF THE SURFACE WARM FRONT. IN FACT...THE STORM PREDICTION CENTER IN NORMAN OKLAHOMA HAS ISSUED TORNADO WATCHES FOR PORTIONS OF LOUISIANA AND MISSISSIPPI. ADDITIONALLY...AT 09/1500 UTC...A SURFACE TROUGH IS ANALYZED ALONG THE SE TEXAS COASTLINE FROM 30N94W TO 28N96W TO 27N97W...WHERE REGIONAL VARIATIONS IN SURFACE WIND SPEED ARE RESULTING IN LOW LEVEL CONVERGENCE...WITH SCATTERED SHOWERS AND THUNDERSTORMS WITHIN 60 NM EITHER SIDE OF THIS SURFACE TROUGH. THE SHOWER AND THUNDERSTORM ACTIVITY PRESENTLY ACROSS THE SE CONUS IS IMPACTING ADJACENT PORTIONS OF THE N GULF COAST. ACROSS THE SE GULF...DEEP LAYER DRY AIR IS INHIBITING DEEP CONVECTION AT THIS TIME. OVER THE NEXT DAY...THE AFOREMENTIONED SURFACE COLD FRONT IS FORECAST TO BEGIN TO TRAVERSE PORTIONS OF 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 N AND NW SURFACE WINDS ARE EXPECTED WITH A STRENGTHENING SURFACE PRESSURE GRADIENT...WITH GALE CONDITIONS DEVELOPING OVER THE NEXT DAY FOR THE NW GULF AND STORM CONDITIONS DEVELOPING OVER THE NEXT DAY OVER THE SW GULF. ALSO...A MODIFIED CONTINENTAL POLAR AIRMASS SUPPORTING RELATIVELY COOLER AND DRIER CONDITIONS IS PRESENT IN THE WAKE OF THE COLD FRONT. THESE CONDITIONS ARE ALSO FORECAST TO MOVE ACROSS PORTIONS OF THE GULF REGION OVER THE NEXT DAY. CARIBBEAN SEA... BROAD ANTICYCLONIC FLOW ALOFT ACROSS THE CARIBBEAN REGION CONTINUES AROUND AN UPPER HIGH N OF VENEZUELA NEAR 12N65W. MID/UPPER-LEVEL MOISTURE CONTINUES STREAMING ACROSS THE NW GULF IN SOUTHWESTERLY FLOW ALOFT E OF THE UPPER HIGH...WITH SCATTERED SHOWERS S OF 13N W OF 77W. ADDITIONALLY...THE INCREASED SURFACE PRESSURE GRADIENT RESULTING FROM THE APPROACH OF THE AFOREMENTIONED COLD FRONT IS SUPPORTING STRONG NE TO E WINDS REACHING GALE FORCE ACROSS PORTIONS OF THE CARIBBEAN. OVER THE E CARIBBEAN...DEEP LAYER DRY AIR IS INHIBITING DEEP CONVECTION. ATLANTIC OCEAN... A COLD FRONT IS OVER THE CENTRAL ATLANTIC EXTENDING FROM NE OF THE DISCUSSION AREA TO 32N48W CONTINUING ALONG 29N52W 27N57W. A STATIONARY FRONT CONTINUES FROM 27N57W TO 25N70W OR NE OF THE BAHAMAS. AHEAD OF THE STATIONARY FRONT A PRE-FRONTAL TROUGH EXTENDS FROM 27N56W TO 24N61W 23N66W. S OF THE FRONT... A 1014 MB SURFACE LOW IS NEAR 16N45W...AND A SURFACE TROUGH IS ALONG 50W FROM 9N-14N SUPPORTING ISOLATED SHOWERS AND THUNDERSTORMS WITHIN 240 NM EITHER SIDE OF THE TROUGH AXIS S OF 12N. IN THE UPPER LEVELS...RIDGING EXTENDS FROM THE CARIBBEAN INTO THE CENTRAL ATLANTIC WITH MOISTURE WRAPPING AROUND THE RIDGE AND INTERACTING WITH THE AFOREMENTIONED CENTRAL ATLANTIC FRONTS...PRODUCING ISOLATED SHOWERS WITHIN 60 NM EITHER SIDE OF THE FRONTS. AN UPPER TROUGH N OF 16N E OF 35W WITH ASSOCIATED ASCENT IN DEEP MOISTURE E OF THE TROUGH IS PRODUCING SCATTERED SHOWERS N OF 18N E OF 35W. ZONAL WESTERLY FLOW ALOFT EXISTS ACROSS THE TROPICS. OVER THE NEXT 24 HOURS...EXPECT THE COLD FRONT TO GENERALLY WEAKEN OVER THE AREA AS THE BULK OF THE UPPER LEVEL SUPPORT SHIFTS NORTHWARD. $$ COHEN/WALTON