000 AGXX40 KNHC 221740 MIMATS MARINE WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 140 PM EDT WED OCT 22 2008 MARINE WEATHER DISCUSSION FOR GULF OF MEXICO... CARIBBEAN SEA AND SOUTHWEST NORTH ATLC S OF 31N W OF 55W. GULF OF MEXICO... LATEST SURFACE ANALYSIS SHOWS STRONG HIGH PRES OVER THE CAROLINAS EXTENDING SOUTHWEST INTO THE N CENTRAL AND NE GULF WATERS...WITH A BROAD AND WEAK LOW PRESSURE OVER THE SOUTHERN YUCATAN AND BELIZE. IN BETWEEN THE TWO...QUIKSCAT...C-MAN ...BUOY...AND SCATTERED SHIP REPORTS INDICATE NE TO E WINDS TO 20 KT FROM 23N TO 28N W OF 90W EARLY THIS AFTERNOON. ALTHOUGH THE FETCH WIDTH HAS BEEN INCREASING...THESE WINDS HAVE NOT BEEN BLOWING ALL THAT LONG. AS SUCH...WAVE HEIGHTS ARE IN THE 4 TO 7 FT RANGE OVER MOST OF THE EASTERN AND CENTRAL GULF WATERS BUT HAVE NOT RISEN OVER 8 FT. SATELLITE IMAGERY AND RADAR OUT OF KEY WEST SHOWS AN INCREASING COVERAGE OF CLOUDS...SHOWERS...AND A FEW TSTMS FROM S OF 25N W OF 90W THROUGH THE FLORIDA STRAITS. OVER THE WESTERN GULF...WHERE THE PRESSURE GRADIENT IS MUCH WEAKER...NE TO E WINDS OF 10 TO 15 KT PREVAIL EXCEPT E TO SE OVER THE NW WATERS. SEAS GENERALLY RANGE FROM 3 TO 6 FT. OVER THE NEXT FEW DAYS...A LARGE CUT-OFF LOW FORMING OVER THE PLAIN STATES WILL ONLY SLOWLY ADVANCE INTO THE MIDWEST AND MISSISSIPPI VALLEY. AS IT DOES SO...AN ASSOCIATED COLD FRONT SHOULD DROP THROUGH TEXAS AND ENTER THE NW GULF/PUSH OFF TX COAST EARLY THU. LARGE-SCALE DIVERGENCE AND LIFT AHEAD OF THE TROUGH SHOULD ALSO RE-ACTIVATE AN OLD FRONTAL BOUNDARY OVER THE SOUTHERN GULF AND CAUSE IT LIFT N AS A WARM FRONT...AS BROAD LOW PRESSURE NOW OVER THE YUCATAN LIFTS NW TO N AND MERGES WITH IT THU. WITH WARM...MOIST AIR BEING TRANSPORTED NORTHWARD OVER A MODIFIED POLAR AIR MASS SITTING OVER THE SE U.S...EXPECT WIDESPREAD CLOUDS...SHOWERS...AND TSTMS NEAR THE BROAD SURFACE LOW MOVING N TO NE OVER THE CENTRAL GULF...WITH STEADY AND SOMETIMES HEAVY RAIN ALSO DIRECTLY AHEAD OF THE ASSOCIATED WARM FRONT. NOAA WAVEWATCH III HAS ADVERTISED AND E TO SE WIND OF 20 TO 30 KT N OF THE WARM FRONT...WITH THE DURATION AND FETCH ENOUGH TO CAUSE WAVE HEIGHTS TO BUILD TO AT LEAST 7 TO 11 FT LATE THU AND FRI. AS SURFACE LOW PRES AND THE ASSOCIATED WARM FRONT CROSS THE FL PANHANDLE FRI MORNING AND AFTERNOON...SE TO S WINDS SHOULD VEER MORE S TO SW AHEAD OF THE COLD FRONT SWEEPING ACROSS THE CENTRAL GULF. MODELS SHOW AN INITIAL BURST OF NW TO N 20 TO 25 KT WINDS OVER THE NW GULF IN THE WAKE OF THE FRONT THU...WHICH SHOULD CAUSE SEAS TO BUILD TO 6 TO 9 FT. THEREAFTER...NW TO N WINDS SHOULD REMAIN IN THE 15 TO 20 KT RANGE AND GRADUALLY DIMINISH GOING INTO EARLY FRI. WEAK HIGH PRES IS FORECAST TO BUILD W OF THE FRONT LATE FRI INTO THE WEEKEND...WITH THE FRONT MOVING SE OF THE AREA EARLY SAT. FOR THE MOST PART...WINDS AND SEAS SHOULD DIMINISH AND SUBSIDE...EXCEPT IN A ZONE SE OF A LINE FROM 29N83W TO 21N96W...WHERE NE WINDS OF UP TO 20 KT SHOULD CONTINUE BLOWING AND RESULT IN 4 TO 7 FT SEAS AND POSSIBLY 8 FT SEAS IN A FEW SPOTS. LONGER-TERM...ALL GLOBAL MODELS TAKE A LARGE CHUNK OF SHORTWAVE ENERGY AND DIVE IT ALMOST DUE S FROM THE GREAT LAKES LATE IN THE WEEKEND TO CARVE OUT A SHARP TROUGH IN THE EASTERN THIRD OF THE CONUS BY MON NEXT WEEK. MOST MODELS ARE FAIRLY SIMILAR WITH THE AMPLITUDE OF THIS FEATURE...BUT THE GFS HAS CONSISTENTLY BEEN A BIT FASTER THAN THE REMAINDER OF THE GUIDANCE. ASSUMING A MORE ECMWF/GFS ENSEMBLE MEAN MODEL CONSENSUS...A STRONG COLD FRONT...THE STRONGEST OF THE FALL SEASON SO FAR...WILL SWEEP INTO THE NORTHERN GULF WATERS EARLY MON AND CROSS MOST OF THE REST OF THE GULF BY MON NIGHT. GFS SHOWS NORTHERLY 20 TO 30 KT WINDS COVERING NEARLY ALL THE GULF...WITH EVEN THE ECMWF SHOWING UP TO 25 KT WINDS. ALTHOUGH NOT CLEAR IN THE GUIDANCE YET...IT WOULD NOT BE SURPRISING TO SEE NEAR GALE FORCE WINDS OVER SOME PART OF THE GULF MON AFTER THE PASSAGE OF THE FRONT WITH SEAS BUILDING TO 8 TO 12 FT. WINDS SHOULD QUICKLY DIMINISH FROM NW TO SE BY TUE DUE TO THE PROGRESSIVE NATURE OF THE UPPER TROUGH. CARIBBEAN... BROAD BUT WEAK SURFACE LOW PRESSURE OVER BELIZE AND THE SOUTHERN YUCATAN IS DRIFTING NW EARLY THIS AFTERNOON AND SHOULD TURN MORE NNW TO N LATER TONIGHT AND THU. SCATTERED CONVECTIVE ACTIVITY ASSOCIATED WITH THIS FEATURE CONTINUES TO AFFECT THE NW CARIBBEAN AND GULF OF HONDURAS...WITH ADDITIONAL CONVECTION SPROUTING UP OVER THE SW CARIBBEAN IN ASSOCIATION WITH A TROPICAL WAVE CURRENTLY ANALYZED ALONG 79W. AS THE LOW SLOWLY AND UNEVENTFULLY EXITS THE NW CARIBBEAN TONIGHT AND THU...THERE SHOULD BE A GRADUAL DECREASE IN UNSETTLED CONDITIONS WHICH HAVE PREVAILED OVER THE NW CARIBBEAN THE LAST FEW DAYS. OTHERWISE...HIGH PRES OVER THE SW ATLC WILL BE REINFORCED THU AND FRI...AS STRONGER HIGH PRES OVER THE CAROLINAS BRIDGES SOUTHWARD. AS A RESULT...MODERATE TO OCCASIONALLY STRONG TRADES SHOULD CONTINUE TO PREVAIL OVER A ZONE FROM 12N TO 18N BETWEEN 67W AND 81W. WAVEWATCH INDICATES SEAS OF UP TO 8 OR 9 FT OVER THE CENTRAL CARIBBEAN IN ASSOCIATION WITH THE ENHANCED TRADES... WITH EASTERLY SWELL PROPAGATING WELL DOWNSTREAM INTO WESTERN CARIBBEAN. OVER THE WEEKEND THOUGH...THE GRADIENT OVER THE CARIBBEAN RELAXES AND THE TRADES DROP OFF CONSIDERABLY OVER PRESENT VALUES AND SEAS SUBSIDE. OF INTEREST NEXT IS THE COLD FRONT FORECAST TO MOVE ACROSS THE GULF THU AND FRI. IT SHOULD EDGE INTO THE YUCATAN CHANNEL LATE SAT OR EARLY SUN AND THEN GET A SECOND PUSH SUN INTO MON...WHICH SHOULD PUSH IT FROM A POSITION FROM 22N81W TO 16N88W. N TO NE WINDS OF 15 TO 20 KT AND SEAS OF 5 TO 8 FT SHOULD BEGIN TO ENTER THE YUCATAN CHANNEL LATER SUN INTO MON...WITH SOME 25 KT WINDS AND 6 TO 9 FT SEAS POSSIBLE LATER MON. OF FINAL NOTE...A WEAK SURFACE LOW FORMING ALONG A HIGH AMPLITUDE TROPICAL WAVE SHOULD MOVE INTO THE NE WATERS OF THE NORTHERN TROPICAL ATLC WATERS LATER TONIGHT THROUGH EARLY FRI. SEVERAL QUIKSCAT PASSES OVER THE LAST DAY OR TWO HAVE CONSISTENTLY SHOWN E TO SE 20 KT WINDS IN ASSOCIATION WITH THIS FEATURE. HOWEVER...MODELS KEEP THE BULK OF THESE WINDS AWAY FROM THE TROPICAL N ATLC WATERS. STILL THOUGH...THERE COULD BE SOME MARGINAL INCREASE IN THE CHANCE FOR SHOWERS OR TSTMS OVER THE NE WATERS DURING THIS PERIOD...PERHAPS ALSO WITH SOME INCREASE IN WINDS AND SEAS. SW N ATLC... LATEST SURFACE ANALYSIS SHOWS AN E-W SURFACE RIDGE ALONG 29-30N ...WITH A FAIRLY STRONG COLD FRONT SWEEPING OFF THE CAROLINA COAST. AS THAT FRONT SWEEPS E BUT N OF THE AREA LATER TODAY AND THU...STRONG HIGH PRES OVER THE CAROLINAS WILL BUILD SOUTHWARD INTO THE SW ATLC AND REINFORCE THE PATTERN WHICH WAS IN PLACE EARLIER IN THE WEEK. AS A RESULT OF THE STRONG HIGH PRES...A LARGE AREA OF NE TO E WINDS OF 20 TO 30 KT IS EXPECTED TO DEVELOP INITIALLY N OF 24N W OF 71W BUT EVENTUALLY OVERSPREAD THE ENTIRE AREA LATE FRI AND SAT. ALREADY SEVERAL C-MAN AND SHIP REPORTS HAVE NE TO E 20 KT WINDS S OF 26N W OF 75W...BUT AN EARLIER QUIKSCAT PASS INDICATED THAT THESE WERE SPOTTY. THE TRUE INCREASE IN WINDS WILL OCCUR LATER TONIGHT INTO THU...WITH THE STRONG WINDS EXPANDING OVER THE WESTERN PART OF THE SW ATLC. BY EARLY FRI...LOW PRES OVER THE EAST CENTRAL GULF SHOULD BE LIFTING N TO NE INTO THE FL PANHANDLE AND CROSSING THE SE CONUS. AS THE ASSOCIATED WARM FRONT CROSSES THE NW WATERS OF THE SW ATLC...WINDS SHOULD VEER MORE E TO SE...BUT WILL REMAIN AT SPEEDS OF 20 TO 30 KT. WITH THIS EVENT EXPECTED TO BE OF A LONG DURATION AND THE FETCH WIDTH LIKELY FAIRLY BROAD...SEAS SHOULD RESPOND BY BUILDING TO 8 TO 13 FT AT A MAX FRI N AND E OF THE BAHAMAS. IN ADDITION...VERY UNSETTLED WEATHER WITH SCATTERED TO NUMEROUS TSTMS WILL BE PRESENT THU INTO AT LEAST EARLY SAT ...WITH THE BULK OF THE PRECIPITATION EXITING LATER SAT. THE ASSOCIATED COLD FRONT SHOULD ARRIVE OVER THE NW WATERS SAT AND MAKE GRADUAL HEADWAY TO THE E. NW WINDS OF 15 TO 20 KT WILL REPLACE THE STRONG EASTERLY FLOW AHEAD OF THE FRONT...WITH SEAS OF 6 TO 9 FT GRADUALLY SUBSIDING AS THE WINDS ALSO TAPER OFF. THE REST OF THE AREA E OF THE BAHAMAS SHOULD BE DOMINATED BY 7 TO 10 FT SEAS IN N TO NE SWELL AT LEAST THROUGH THE WEEKEND. LONGER-TERM...AS DESCRIBED ABOVE...A SECOND SHARP TROUGH DIGGING INTO THE EXTREME EASTERN CONUS MON NEXT WEEK WILL DELIVER THE STRONGEST COLD FRONT OF THE FALL SEASON SO FAR TO THE GULF FIRST AND EVENTUALLY THE SW ATLC WATERS. ADOPTING A SLOWER ECMWF/GFS ENSEMBLE MEAN SOLUTION...THE FRONT SHOULD ENTER THE FAR NW WATERS MON AFTERNOON AND SWEEP RAPIDLY SE BY EARLY TUE. EXPECT MODERATE TO STRONG S TO SW WINDS AHEAD OF THE FRONT...WITH NW 20 TO 25 KT WINDS BUILDING BEHIND IT LATER ON MON AND EARLY TUE. MEANWHILE...FARTHER E...THE N TO NE SWELL SHOULD BE IN THE PROCESS OF GRADUALLY DECAYING EARLY NEXT WEEK. ATLANTIC... NONE. CARIBBEAN... NONE. GULF OF MEXICO... NONE. FORECASTER KIMBERLAIN. TROPICAL PREDICTION CENTER.