000 AGXX40 KNHC 170717 MIMATS MARINE WEATHER DISCUSSION NWS NATIONAL HURRICANE CENTER MIAMI FL 220 AM EST THU NOV 17 2011 MARINE WEATHER DISCUSSION FOR THE GULF OF MEXICO...CARIBBEAN SEA AND TROPICAL N ATLC...AND SOUTHWEST NORTH ATLC S OF 31N W OF 55W. GULF OF MEXICO... FREQUENT LIGHTNING IS OBSERVED ALONG A LINE NEAR THE FRONTAL TROUGH OVER THE NE GULF THIS MORNING. THIS TROUGH WILL QUICKLY BE OVERTAKEN BY THE COLD FRONT THAT HAS ENTERED THE NW GULF. THE MODELS HAVE TRENDED ABOUT 6-12 HOURS FASTER COMPARED TO THIS TIME LAST NIGHT WITH THE FRONTAL TIMING...CARRYING THE WEAKENING FRONT INTO S FLORIDA FRI. THE GFS CONTINUES TO SHOW WINDS ABOUT 5 KT STRONGER BEHIND THE FRONT THAN THE ECMWF IN THE MIDDLE AND EASTERN GULF TODAY AND TONIGHT. CURRENTLY...THE STRONGER GFS IS VERIFYING BETTER THAN THE ECMWF WITH THE WINDS BEHIND THE FRONT IN THE NW GULF WHERE BUOY 42020 REPORTED 25 KT NE WINDS AT 0600 UTC. WITH THE GFS AND ECMWF BOTH TRENDING FASTER CARRYING THE FRONT SOUTHWARD AND THE UKMET HEDGING TOWARD THE STRONGER GFS NOW...WILL LEAN HEAVILY ON THE GFS FOR THE FORECAST WITH THIS FRONT AND THE SE RETURN FLOW EXPECTED ON THE BACKSIDE OF THE HIGH PRES TRAILING THE FRONT. CARIBBEAN SEA AND TROPICAL N ATLC... HIGH PRES N OF THE AREA CONTINUES TO CREATE A TIGHT ENOUGH PRES GRADIENT ACROSS THE CARIBBEAN TO SUPPORT FRESH NE TRADE WINDS PRIMARILY OVER THE CENTRAL CARIBBEAN ACCORDING TO THE ASCAT PASS FROM 0132 UTC. THESE FRESH TRADES WILL DIMINISH LATER TODAY AS A COLD FRONT MOVES THROUGH THE NORTHERN GULF OF MEXICO INTO THE SW N ATLC...DISLODGING THE RIDGE AXIS CURRENTLY IN PLACE THERE ALONG 27N. FRESH NE WINDS ALSO LIE OVER THE TROPICAL N ATLC N OF 20N WHERE THE PRES GRADIENT IS TIGHT BETWEEN THE AFOREMENTIONED RIDGE AND LOW LEVEL TROUGHING ALONG 45W-50W THAT IS THE REFLECTION OF BROAD TROUGHING ALOFT THAT ENCOMPASSES BOTH ENERGY THAT HAS SPLIT FROM AN OLD FRONTAL BOUNDARY TO THE NE AND ENERGY THAT HAS SPILLED INTO THE THE TROUGH FROM THE NW. THERE IS CONSIDERABLE DISAGREEMENT WITH THE EVOLUTION OF THIS TROUGHING...WITH THE GFS DEVELOPING A STRONG LOW PRES SYSTEM BY SUN THAT ONLY HAS SUPPORT FROM THE CMC MODEL. THE GFS SPITS OUT OVER 6 INCHES OF PRECIPITATION EACH 6 HOUR PERIOD ON FRI. THIS SEEMS VERY GENEROUS AND IS LIKELY THE RESULT OF CONVECTIVE FEEDBACK. HOWEVER...THE GEFS MEAN CARRIES A DISTINCT LOW FROM 15N TO 25N BETWEEN 50W AND 60W SAT THROUGH MON...SO THERE IS SOME AGREEMENT AMONG THE GFS ENSEMBLE MEMBERS ON THIS SCENARIO. FOR NOW CONFIDENCE REMAINS LOW AND THE FORECAST WILL BLEND THE GFS AND ECMWF SOLUTIONS WHICH KEEPS THE STRONGEST WINDS AND HIGHEST SEAS PRIMARILY IN THE NW CORNER OF THE TROPICAL N ATLC ZONE WHERE THE PRES GRADIENT WILL REMAIN GREATEST BETWEEN THIS TROUGHING AND RIDGING OVER THE SW N ATLC. SW N ATLC S OF 31N W OF 55W... THE 0134 UTC ASCAT PASS AND SHIP/BUOY OBSERVATIONS SHOW FRESH TRADE WINDS ARE CONFINED PRIMARY S OF 26N E OF THE BAHAMAS IN THE AREA S OF THE RIDGE AXIS WHICH EXTENDS ALONG 27N. A FRONTAL TROUGH WILL MOVE OFF THE N FL COAST THIS MORNING. THIS TROUGH CURRENTLY HAS NUMEROUS STRONG THUNDERSTORMS ASSOCIATED WITH IT. FRESH S TO SW WINDS LIE AHEAD OF THE TROUGH WITH BUOYS 41012 AND 41009 BOTH REPORTING 19 KT AT 0400 UTC.THE TROUGH WILL BE OVERTAKEN BY A COLD FRONT THIS AFTERNOON AND THE RIDGE WILL BE SHOVED NORTHEASTWARD AHEAD OF IT. AS EXPLAINED IN THE GULF OF MEXICO SECTION...THE MODELS HAVE TRENDED FASTER CARRYING THE FRONT THROUGH FLORIDA TODAY THROUGH FRI. THE GFS IS STRONGER WITH THE WIND FORECAST BOTH IN THE GULF AND THE SW N ATLC...BUT WAS INITIALIZED BETTER THAN THE ECMWF AND HAS MORE SUPPORT FOR STRONGER WINDS FROM THE UKMET THIS RUN. BOTH THE GFS AND UKMET CARRY 25 KT NW WINDS BEHIND THE FRONT THIS EVENING WHILE THE ECMWF IS 5 KT WEAKER. WILL STICK WITH THE STRONGER FORECAST HERE. RIDGING WILL AGAIN BUILD OVER THE AREA BEHIND THE COLD FRONT FRI. WINDS WILL REMAIN FRESH TO STRONG OVER MUCH OF THE SW N ATLC OFFSHORE ZONE...SAVE NW WATERS...OVER THE WEEKEND AS HIGH PRES BEHIND THE FRONT BUTTS UP AGAINST THE PERSISTENT TROUGHING JUST E OF THE AREA AND N OF THE TROPICAL N ATLC ZONE. THERE IS CONSIDERABLE DISAGREEMENT IN THE DETAILS WITH THIS TROUGHING...WITH THE GFS DEVELOPING A STRONG LOW PRES SYSTEM BY SUN THAT ONLY HAS SUPPORT FROM THE CMC MODEL. THE GFS SPITS OUT OVER 6 INCHES OF PRECIPITATION EACH 6 HOUR PERIOD ON FRI. THIS SEEMS VERY GENEROUS AND IS LIKELY THE RESULT OF CONVECTIVE FEEDBACK. HOWEVER...THE GEFS MEAN CARRIES A DISTINCT LOW FROM 15N TO 25N BETWEEN 50W AND 60W SAT THROUGH MON...SO THERE IS SOME AGREEMENT AMONG THE GFS ENSEMBLE MEMBERS ON THIS SCENARIO. FOR NOW CONFIDENCE REMAINS LOW AND THE FORECAST WILL BLEND THE GFS AND ECMWF SOLUTIONS. WARNINGS... GULF OF MEXICO... .NONE. .CARIBBEAN SEA AND TROPICAL N ATLC... .NONE. .SW N ATLC... .NONE. FOR ADDITIONAL INFORMATION PLEASE VISIT HTTP://WWW.HURRICANES.GOV/MARINE $$ FORECASTER SCHAUER