000 AXNT20 KNHC 051747 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 705 PM EST SAT DEC 05 2009 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 1700 UTC. ...ITCZ... THE ITCZ AXIS IS CENTERED ALONG 8N12W 6N24W 2N36W EQ52W. SCATTERED MODERATE CONVECTION IS ALONG THE AXIS BETWEEN 28W-31W. ...DISCUSSION... GULF OF MEXICO... AS OF 1500 UTC...A COLD FRONT EXTENDS ACROSS THE SE GULF OF MEXICO FROM CENTRAL FLORIDA N OF FT MYERS AT 27N82W ALONG 24N83W N OF W CUBA TO THE YUCATAN CHANNEL ENDING NEAR 21N87W. SIGNIFICANT MOISTURE ACROSS THE SE GULF ALONG WITH SURFACE CONVERGENCE NEAR THE FRONT IS PRODUCING A LINE OF STRONG SHOWERS/THUNDERSTORMS EXTENDING WITHIN 100 NM AHEAD OF THE FRONT FROM W CUBA ACROSS S/CENTRAL FLORIDA...EVIDENT IN RADAR IMAGERY. IN FACT...MUCH OF THE SRN HALF OF THE FLORIDA PENINSULA IS UNDER A TORNADO WATCH UNTIL MID-AFTERNOON TODAY. THE FRONT IS SUPPORTED BY A DEEP LAYER TROUGH COVERING THE ERN CONUS EXTENDING INTO THE CENTRAL GULF OF MEXICO. DIFFLUENT FLOW ALOFT BETWEEN THIS TROUGH AND AN UPPER LEVEL RIDGE EXTENDING FROM THE CARIBBEAN INTO THE W ATLC IS ALSO ENHANCING THE STRONG SHOWER ACTIVITY AFFECTING FLORIDA. A DRY COLD AIR MASS ACCOMPANIED BY SUBSIDENCE ALOFT AND SURFACE HIGH PRESSURE CENTERED OVER SE TEXAS BUILDS BEHIND THE FRONT. THE STRONG PRESSURE GRADIENT BETWEEN THIS HIGH PRESSURE AND THE LOWER PRESSURE ACROSS THE SE GULF CONTINUES TO SUPPORT GALE FORCE NW TO N WINDS IN THE SW GULF S OF 21N W OF 95W. THESE WINDS ARE EXPECTED TO DIMINISH LATER THIS AFTERNOON AS THE COLD FRONT AND ASSOCIATED LOWER PRESSURE CONTINUES TO PUSH EWD. EXPECT CONTINUED STRONG SHOWERS/THUNDERSTORMS TO ACCOMPANY THE FRONT AS IT SHIFTS E. CARIBBEAN SEA... STRONG SUBSIDENCE AND DRY AIR ALOFT CONTINUES TO BRING FAIR WEATHER TO THE MAJORITY OF THE CARIBBEAN TODAY. SHOWERS/THUNDERSTORMS HAVE STARTED TO AFFECT PORTIONS OF W CUBA AHEAD OF THE COLD FRONT IN THE SE GULF OF MEXICO EXTENDING N OF W CUBA TO THE YUCATAN CHANNEL. MODERATE TO FRESH TRADEWINDS ARE ACROSS MUCH OF THE BASIN WITH STRONGER WINDS NEAR THE COAST OF COLOMBIA. IN THE UPPER LEVELS...AN UPPER LEVEL RIDGE COVERS THE MAJORITY OF THE AREA EXTENDING FROM NICARAGUA ACROSS THE WINDWARD PASSAGE INTO THE W ATLC. A NARROW UPPER LEVEL TROUGH...STILL ACCOMPANIED BY DRY AIR ALOFT...EXTENDS FROM THE CENTRAL ATLC ACROSS THE LESSER ANTILLES TO NRN COLOMBIA. EXPECT THE COLD FRONT IN THE SE GULF OF MEXICO TO PUSH INTO THE FAR NW CARIBBEAN BRINGING SHOWERS/THUNDERSTORMS WITH IT BEFORE DISSIPATING LATE SUN. ATLANTIC OCEAN... AS OF 1500 UTC...A COLD FRONT DRAPES ACROSS THE W ATLC ENTERING THE DISCUSSION AREA NEAR 32N77W ALONG 28N79W TO THE CENTRAL FLORIDA COAST NEAR VERO BEACH AT 28N80W CONTINUING ACROSS CENTRAL FLORIDA INTO THE SE GULF OF MEXICO. RADAR IMAGERY AND RECENT LIGHTNING DATA INDICATE SHOWERS/THUNDERSTORMS WITHIN 90 NM EITHER SIDE OF THE FRONT WITH THE STRONGEST ACTIVITY ALONG AND E OF THE FRONT AXIS. THE FRONT IS SUPPORTED BY A DEEP LAYER TROUGH COVERING THE ERN CONUS EXTENDING INTO THE CENTRAL GULF OF MEXICO. DIFFLUENT FLOW ALOFT BETWEEN THIS UPPER TROUGH AND AN UPPER LEVEL RIDGE EXTENDING FROM THE CARIBBEAN ACROSS THE SE BAHAMAS CONTINUING NE SUPPORTS THE STRONG SHOWER ACTIVITY NEAR THE FRONT. THE UPPER LEVEL RIDGE IS ALSO SUPPORTING A BROAD SURFACE RIDGE COVERING THE REMAINDER OF THE W ATLC ANCHORED BY A 1025 MB HIGH NEAR 32N51W. IN THE CENTRAL ATLC...A PAIR OF SURFACE TROUGHS CAUSE WEAKNESSES IN THE SURFACE RIDGE. THE FIRST EXTENDS FROM A STATIONARY FRONT N OF THE AREA EXTENDING FROM 31N37W TO 24N49W. ISOLATED SHOWERS ARE WITHIN 120 NM SE OF THE TROUGH AXIS. THE SECOND SURFACE TROUGH EXTENDS FROM 21N46W TO 15N48W...AND IS A SURFACE REFLECTION OF AN UPPER LEVEL LOW CENTERED NEAR 17N45W. ISOLATED SHOWERS ARE ALONG THE TROUGH AXIS. ANOTHER SURFACE RIDGE DOMINATES THE E ATLC ANCHORED BY A 1024 MB HIGH NEAR 31N23W. AN UPPER LEVEL TROUGH EXTENDING FROM THE AFOREMENTIONED UPPER LOW TO THE CANARY ISLANDS SUPPORTS STRONG WLY WINDS ALOFT ACROSS THE TROPICAL ATLC DRAWING MOISTURE AND HIGH CLOUDS FROM THE ITCZ ACROSS THE CAPE VERDE ISLANDS TO THE AFRICA COAST. $$ WALTON