000 AXNT20 KNHC 302357 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 705 PM EST SUN NOV 30 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... FROM GUINEA/SIERRA LEONE IN AFRICA NEAR 10N12W TO 5N30W 4N40W INTO NORTHEASTERN BRAZIL NEAR 02N51W. SCATTERED MODERATE CONVECTION EXISTS WITHIN 270 NM S OF AXIS BETWEEN 19W AND 34W AND WITHIN 90 NM N OF AXIS BETWEEN 26W AND 36W. ...DISCUSSION... THE GULF OF MEXICO... A VIGOROUS...DEEP-LAYERED TROUGH EXTENDS FROM THE EAST CENTRAL CONUS INTO THE GULF OF MEXICO...CARRYING WITH IT AN ASSOCIATED STRONG COLD FRONT FROM JUST E OF TALLAHASSEE THROUGH 26N86W TO THE N CENTRAL YUCATAN. THE FRONT THEN CONTINUES SW TO W THROUGH THE NORTHERN ISTHMUS OF TEHUANTEPEC AND A LARGE PART OF NORTHERN MEXICO. STRONG DYNAMICS ASSOCIATED WITH A STRONG 150 KT JET STREAK ROTATING THROUGH THE TROUGH OVER THE SOUTHEASTERN STATES HAVE HELPED PRODUCE A NEARLY SOLID LINE OF CONVECTION JUST AHEAD OF THE MAIN COLD FRONT. ON TOP OF THE CONVECTION SHIPS ...BUOYS...AND C-MAN STATIONS OVER THE EASTERN GULF ARE REPORTING SOUTHERLY 20 TO SOMETIMES 30 KT WINDS WITH GUSTS POSSIBLY TO GALE FORCE IN RAPIDLY BUILDING SEAS. STRONG SOUTHERLY SURFACE WINDS ADVECTING LOW-LEVEL MOISTURE AND INSTABILITY NORTHWARD AHEAD OF THE COLD FRONT SHOULD CONTINUE TO CREATE AN ENVIRONMENT FAVORABLE FOR SEVERE WEATHER OVER THE SOUTHERN HALF OF FLORIDA AND THE SE GULF OF MEXICO EARLY TONIGHT. MOREOVER...AN IMPRESSIVE LAYER OF DEEP SHEAR ASSOCIATED WITH PARTICULARLY STRONG SOUTHWESTERLY FLOW ALOFT WILL ENHANCE THE POTENTIAL FOR SEVERE THUNDERSTORMS OVER THIS AREA. FOR THIS REASON...THE STORM PREDICTION CENTER HAS ISSUED A TORNADO WATCH FOR PORTIONS OF S FLORIDA AND THE ADJACENT COASTAL WATERS THROUGH AT LEAST THROUGH THIS EVENING. SURFACE OBSERVATIONS AND DOPPLER RADAR ALREADY INDICATE A BROKEN SQUALL LINE...WHICH HAS FORMED ALONG A PRE-FRONTAL TROUGH RUNNING FROM 31N80W TO JUST SE OF FT MYERS AS OF 2100 UTC. THE SQUALL LINE IS ADVANCING RAPIDLY SOUTHEASTWARD TOWARD SE FLORIDA AND THE KEYS. BEHIND THE FRONT...LOW-LEVEL DIVERGENCE HAS GIVEN WAY TO CLEARING SKIES...WITH RAPID PRESSURE RISES LEADING TO A NW TO N 20 TO 25 KT FLOW. SURFACE DATA ALSO SUGGESTS THAT A SECONDARY COLD FRONT HAS SURGED INTO THE FAR NW WATERS ALONG A LINE FROM NEAR LAFAYETTE LA TO NEAR CORPUS CHRISTI TX. PER MODEL GUIDANCE...WINDS SHOULD FURTHER INCREASE BEHIND THIS SECONDARY BOUNDARY...WITH W TO NW WINDS OF 20 TO 30 KT ON AVERAGE. THERE IS ALSO A GOOD CHANCE OF GALE FORCE WINDS FOR A BRIEF TIME OVER THE N CENTRAL AND NE OFFSHORE WATERS BEGINNING LATER TONIGHT INTO EARLY MON MORNING. THE CARIBBEAN SEA... SATELLITE PICTURES AND AND EARLIER ASCAT PASS REVEALS THAT A WEAK SURFACE LOW JUST N OF PANAMA YESTERDAY HAS TRACKED WNW TO NW OVER THE LAST 24 HOURS. LATEST OBSERVATIONS SUGGEST THAT THE 1010 MB LOW IS NOW ROUGHLY NEAR 12N82W MOVING JUST W OF DUE N AROUND 10 KT. LOW-LEVEL CONVERGENCE NEAR THIS SURFACE LOW IS SUPPORTING SCATTERED SHOWERS AND THUNDERSTORMS S OF 12N W OVER PANAMA...COSTA RICA....NICARAGUA AND THE ADJACENT CARIBBEAN WATERS. ADDITIONAL THUNDERSTORMS HAVE DEVELOPED ALONG A LOW -LEVEL CONFLUENT AXIS...A DEMARCATION BETWEEN THE EASTERN TRADES AND SOUTHERLY FLOW SE OF THE SURFACE LOW. ALL OF THIS ACTIVITY IS BEING ENHANCED BY UPPER LEVEL DIFFLUENCE IN THE VICINITY OF AN UPPER RIDGE PRESENT OVER THE W CARIBBEAN...WITH THE AXIS OF THIS UPPER RIDGE EXTENDING FROM CENTRAL COLOMBIA NEAR 07N75W TO CENTRAL NICARAGUA. OVER THE EASTERN HALF OF THE CARIBBEAN...DEEP LAYER SUBSIDENCE AND DEEP LAYER DRY AIR ARE IN PLACE RESULTING IN FAIR WEATHER ...WHERE NORTHWESTERLY FLOW ALOFT IS PRESENT. IN ADDITION... ENHANCED SURFACE RIDGING FROM THE CENTRAL ATLANTIC INTO THE CENTRAL CARIBBEAN IS RESULTING IN INCREASED TRADES MOSTLY E OF 70W. ELSEWHERE...SOUTHERLY FLOW OVER THE NW CARIBBEAN HAS BEEN INCREASING THROUGHOUT THE DAY. IN FACT...AN EARLIER ASCAT PASS OVER THE REGION SUGGESTED A BROAD AREA OF 20 TO 25 KT WINDS... WITH THE STRONGEST WINDS MOSTLY N OF 18N W OF 82W. MODELS FORECAST THE SURFACE COLD FRONT CURRENTLY OVER THE GULF OF MEXICO TO REACH THE YUCATAN CHANNEL AND THEN THE FAR NW CARIBBEAN EARLY MON MORNING. FOLLOWING ITS PASSAGE...STRONG NORTHERLY FLOW OF 20 TO 30 KT SHOULD DEVELOP IN THE NW CARIBBEAN ...WITH THE FRONT SETTLING ALONG AN AXIS FROM SE CUBA THROUGH 15N81W TO NORTHERN COSTA RICA BY TUE EVENING. THE ATLANTIC OCEAN... THE DEEP-LAYERED TROUGH MENTIONED ABOVE OVER THE EAST CENTRAL CONUS HAS ALREADY BEGUN TO IMPACT THE SOUTHWEST NORTH ATLANTIC WATERS. THE PRESSURE GRADIENT BETWEEN ENHANCED LOW-LEVEL SUBTROPICAL RIDGING NEAR 28N56W AND DEEPENING LOW PRESSURE OVER THE CAROLINAS HAS RESULTED IN A SOUTHERLY GALE N OF 27N W OF 72W. CONFIRMING THIS IS BUOY 41010 NEAR 29N78.5W...WHICH HAS BEEN REPORTING NEAR CONTINUOUS GALE FORCE WINDS AND SEAS UP TO 17 FT DURING THE LAST FEW HOURS. S TO SW WINDS OF 30 TO 40 KT SHOULD CONTINUE N OF 27N W OF 72W FOR AT LEAST THE NEXT 6 TO PERHAPS 12 HOURS AND THEN BEGINNING TO DIE DOWN A BIT BY MON AFTERNOON. BETWEEN NOW AND THEN THE STRONG SURFACE COLD FRONT SWEEPING ACROSS THE GULF WILL PUSH INTO THE SOUTHWEST NORTH ATLANTIC ...ACCOMPANIED BY A LINE OF STRONG TO SEVERE THUNDERSTORMS. STRONG THUNDERSTORMS HAVE ALREADY DEVELOPED ALONG A FAST-MOVING SQUALL LINE... EXTENDING FROM 31N80W TO SOUTHEAST FLORIDA. LARGE- SCALE CONDITIONS OF STRONG UPPER-LEVEL DIVERGENCE...IMPRESSIVE MOISTURE ADVECTION AND INCREASING INSTABILITY...AS WELL AS DEEP-LAYERED SHEAR ARE ALL LIKELY TO CONTRIBUTE TO ADDITIONAL STRONG TO POSSIBLY SEVERE THUNDERSTORMS OVER THE FLORIDA PENINSULA AND ADJACENT WATERS INTO TONIGHT. AT PRESENT...A TORNADO WATCH IN EFFECT FOR PORTIONS OF FLORIDA AND THE ADJACENT COASTAL WATERS UNTIL 8 PM EST THIS EVENING. OTHERWISE...THE ENHANCED SUBTROPICAL RIDGE MENTIONED ABOVE NEAR 28N56W IS RESPONSIBLE FOR A BROAD ZONE OF INCREASED TRADES OVER THE TROPICAL NORTH ATLANTIC...GENERALLY FROM 10N TO 23N BETWEEN 45W AND 65W. THESE WINDS ARE EXPECTED TO PERSIST FOR THE NEXT DAY OR TWO...RESULTING IN SEAS BUILDING TO 7 TO 11 FT E OF THE LESSER ANTILLES IN NE SWELL. FINALLY...A BROAD...COMPLEX AREA OF LOW PRESSURE IS BEGINNING TO FORM N OF THE AREA ALONG 35W IN ASSOCIATION WITH A MID- TO UPPER-LEVEL TROUGH OVER THE NORTHEAST ATLANTIC IN THE PROCESS OF CUTTING OFF. WITHIN THE NEXT FEW DAYS...THE ASSOCIATED SURFACE LOW PRESSURE SHOULD DIP INTO THE FORECAST WATERS AND BEGIN TRACKING WESTWARD UNDERNEATH BLOCKING HIGH PRESSURE TO THE NORTH. MODERATE TO STRONG NORTHEASTERLY FLOW IS EXPECTED TO FORM BETWEEN IT AND THE ENHANCED SURFACE RIDGE TO THE WEST ...ULTIMATELY LEADING TO BUILDING SEAS IN NE SWELL. OF NOTE...NOVEMBER 30 MARKS THE CONCLUSION OF THE 2008 ATLANTIC HURRICANE SEASON. DURING THIS SEASON...SIXTEEN NAMED TROPICAL CYCLONES OCCURRED. OF THESE SIXTEEN...EIGHT WERE HURRICANES...OF WHICH FIVE WERE MAJOR HURRICANES OF SAFFIR-SIMPSON CATEGORY THREE STRENGTH OF STRONGER. THIS SEASON WAS THE FIRST EVER WHEN SIX CONSECUTIVE TROPICAL CYCLONES MADE LANDFALL ON THE CONUS MAINLAND. OVERALL...THE 2008 HURRICANE SEASON IS TIED AS THE FOURTH MOST ACTIVE IN TERMS OF NUMBER OF NAMED STORMS AND MAJOR HURRICANES...AND IS ALSO TIED AS FIFTH MOST ACTIVE IN TERMS OF NUMBER OF HURRICANES SINCE 1944...THE BEGINNING OF THE AERIAL RECONNAISSANCE ERA. FINALLY...THIS IS THE TENTH SEASON TO PRODUCE ABOVE-NORMAL TROPICAL CYCLONE ACTIVITY SINCE 1995 WHEN THE CURRENT ACTIVE HURRICANE ERA BEGAN. ADDITIONALLY...A TOTAL OF 64 TROPICAL WAVES MOVED OFF THE COAST OF AFRICA THIS SEASON WHICH IS NEAR THE SEASONAL AVERAGE. $$ KIMBERLAIN/COHEN/RUBIO