000 AGXX40 KNHC 280726 MIMATS MARINE WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 230 AM EST WED JAN 28 2009 MARINE WEATHER DISCUSSION FOR GULF OF MEXICO... CARIBBEAN SEA AND SOUTHWEST NORTH ATLC S OF 31N W OF 55W. UPPER LEVEL PATTERN OVER THE FORECAST AREA IS CURRENTLY UNDER TRANSITION AS A VIGOROUS DEEP LAYER TROUGH OVER THE SOUTHERN PLAINS IS EJECTED EASTWARD. DEEP ATMOSPHERIC LIFT ASSOCIATED WITH THIS FEATURE HAS CAUGHT UP TO AN ELONGATED FRONTAL ZONE OVER THE SE CONUS...WHICH IS NOW SURGING SOUTHWARD AS A COLD FRONT OVER TEXAS AND N MEXICO IN RESPONSE TO THE DEVELOPMENT OF A SURFACE LOW ALONG THE FRONT OVER N MISSISSIPPI. THIS FRONT HAS MOVED OFF THE SE TEXAS COAST AS OF 28/0600 UTC...WITH NW TO N WINDS OF 20 TO 30 KT FOLLOWING FRONTAL PASSAGE. EXPECT THE FRONT TO CONTINUE SURGING SOUTH TONIGHT...WITH THE FASTEST SOUTHWARD MOTION ALONG THE MEXICO COASTLINE. POST-FRONTAL WINDS WITH THIS INITIAL SURGE ARE FORECAST TO DECREASE BY WED NIGHT AS THE ASSOCIATED DEEP TROUGH MENTIONED EARLIER LIFTS NORTHEASTWARD OF THE REGION AND THE UPSTREAM SURFACE HIGH TAKES A MORE NORTHEASTWARD TRACK AWAY FROM THE GULF. AHEAD OF THE FRONT...A 1028 MB SURFACE HIGH IN THE WESTERN N ATLC IS INDUCING SOUTHEASTERLY RETURN FLOW. THESE WINDS ARE RELAXING SOMEWHAT WITH THE DEPARTURE OF THE HIGH AND APPROACH OF THE FRONT. HOWEVER...THE INCREASED PRESSURE GRADIENT CONTINUES TO CAUSE STRONG EASTERLY TRADES ACROSS THE CARIBBEAN BASIN AND SW N ATLC. THE STRONGEST OF THESE WINDS ARE NEAR THE COAST OF COLOMBIA...WHERE THE 28/2230 UTC HIGH-RESOLUTION QUIKSCAT PASS DEPICTS WINDS TO 35 KT. THUS...THE GALE WARNING HAS BEEN CONTINUED FOR THIS REGION. THIS MARGINAL GALE EVENT WILL LIKELY PERSIST THROUGH TONIGHT...AS THE TRADE WIND FLOW FORCED CYCLONICALLY AROUND THE HIGHER TERRAIN NEAR COLOMBIA RESULTS IN A LOCAL ENHANCEMENT. THESE TRADES WILL MAINTAIN 8 TO 11 FT SEAS ACROSS A LARGE PART OF THE CARIBBEAN AND SW N ATLC...WITH SEAS TO 13 FT NEAR THE COAST OF COLOMBIA. OVER THE NEXT DAY...THE AFOREMENTIONED FRONT OVER THE GULF IS FORECAST TO SLOW ITS SOUTHWARD MOTION AS ITS UPPER SUPPORT LIFTS NORTHEASTWARD. MEANWHILE...INCREASING COLD AIR ADVECTION AND ASSOCIATED HEIGHT FALLS IN THE MID/UPPER-LEVELS WILL INFILTRATE MUCH OF THE CONUS...RESULTING IN THE DEVELOPMENT OF A LONGWAVE TROUGH OVER MUCH OF THE CONUS. IN TURN...THIS WILL STRENGTHEN SUBSIDENCE AND BUILD A SURFACE HIGH UPSTREAM OF THE TROUGH AXIS OVER THE SOUTHERN PLAINS. ONCE THE LONGWAVE TROUGH IS EJECTED EASTWARD BY AN APPROACHING UPSTREAM UPPER LEVEL JET MAXIMUM AND A DEVELOPING WEST CONUS COAST RIDGE...GFS AND ECMWF MOVE THE SURFACE HIGH SOUTHEASTWARD OVER THE NW GULF...CAUSING THE FRONT TO SURGE SOUTHEASTWARD THURSDAY NIGHT AND FRIDAY. THIS IS SEVERAL HOURS EARLIER THAN PREVIOUS MODEL RUNS...LIKELY REFLECTING THE TRANSITION TO A MORE PROGRESSIVE UPPER PATTERN. CORRESPONDINGLY...INCREASING N TO NE GRADIENT FLOW IN THE WAKE OF THE FRONT WILL REACH SPEEDS OF 25 TO 30 KT OVER A LARGE AREA OF THE GULF. OPERATIONAL AND ENSEMBLE MODELS HAVE TRENDED UPWARD AND COME INTO BETTER CONSISTENCY SINCE YESTERDAY AT THIS TIME WITH REGARD TO THE THREAT FOR GALE FORCE WINDS ACROSS PORTIONS OF THE SW GULF OF MEXICO...PARTICULARLY THAT PORTION CLOSEST TO THE MEXICO COAST. THIS SAME FRONT WILL MOVE OFF THE SE CONUS INTO THE W ATLC ON THURSDAY NIGHT...WITH INCREASING SW FLOW AHEAD OF THE FRONT. ON SATURDAY...GFS INDICATES SOME POTENTIAL FOR GALE FORCE GUSTS WITH STEEPER LAPSE RATES AHEAD OF THE FRONT COINCIDING WITH AN INCREASING LOW-LEVEL JET ASSOCIATED WITH THE FRONT. ECMWF IS SUBSTANTIALLY LESS AGGRESSIVE WITH THIS JET...BOTH WITH REGARD TO ITS MAGNITUDE AND ELEVATED NATURE. THIS CURRENTLY SUGGESTS WINDS UNDER GALE FORCE. A SECONDARY SURGE OF COLD AIR ADVECTION ACROSS THE SW N ATLC COMES ON SAT WITH THE EJECTION OF THE LONGWAVE TROUGH. MODELS CONTINUE TO TREND UPWARD WITH THE SURFACE WIND SPEEDS WITH THIS SECONDARY SURGE. THE BEST CHANCE FOR GALES WILL BE N OF THE AREA...HOWEVER TIME-HEIGHT ANALYSES DEPICT THE MIXED LAYER COINCIDING WITH A LOW-LEVEL JET THAT IS SOMEWHAT WEAKER THAN THE PREFRONTAL LOW LEVEL JET. THIS SUGGESTS THAT WINDS TO 30 KT WILL BE A CONCERN ON SAT N OF 29N...THOUGH THE THREAT FOR GALES IS RATHER LOW...WITH LARGE SPREAD IN SURFACE WIND SPEED PRESENT AMONG MEMBERS OF THE GFS ENSEMBLES. WAVE HEIGHTS IN THE WAKE OF THE FRONT WILL INCREASE TO AS HIGH AS 12 FT OVER THE GULF OF MEXICO FRI EVENING AND AS HIGH AS 16 FT OVER THE W ATLC SATURDAY. ALSO...A MUCH WEAKER COLD FRONT WILL SKIRT NORTHERN PORTIONS OF THE FORECAST AREA IN THE CENTRAL ATLC FOLLOWED BY 20 KT NORTHEASTERLY WINDS AND WAVE HEIGHTS UP TO 14 FT IN NW SWELL. ALSO...IN THE WAKE OF THIS WEAKER FRONT...A SURFACE HIGH WILL STRENGTHEN TRADES ACROSS THE SW N ATLC THIS WEEKEND. ATLANTIC... NONE. CARIBBEAN... GALE WARNING AMZ084 AND AMZ086 THROUGH TONIGHT. GULF OF MEXICO... NONE. FORECASTER COHEN. TROPICAL PREDICTION CENTER.