000 AGXX40 KNHC 270729 MIMATS MARINE WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 230 AM EST TUE JAN 27 2009 MARINE WEATHER DISCUSSION FOR GULF OF MEXICO... CARIBBEAN SEA AND SOUTHWEST NORTH ATLC S OF 31N W OF 55W. NEARLY ZONAL FLOW IN THE MID AND UPPER LEVELS PRESENTLY RESIDES OVER MUCH OF THE FORECAST AREA. THIS IS KEEPING THE MAJORITY OF CONTINENTAL POLAR AIRMASS SURGES NORTH OF THE FORECAST AREA. HOWEVER...BY LATE WEEK...THE UPPER PATTERN IS FORECAST TO BECOME MORE AMPLIFIED...AS A VIGOROUS UPPER LEVEL TROUGH OVER THE EAST PACIFIC IS EJECTED EASTWARD OVER THE CONUS. IN THE MEANTIME...A 1027 MB SURFACE HIGH IN THE WESTERN N ATLC IS INDUCING SOUTHEASTERLY RETURN FLOW ACROSS THE GULF REGION. THESE WINDS ARE EXCEEDING 20 KT BASED ACROSS THE NW GULF BASED ON THE 28/0300 UTC ASCAT PASS...IN RESPONSE TO THE LOCALLY-STEEPENED SURFACE PRESSURE GRADIENT TO THE S OF SURFACE FRONT OVER THE SOUTHERN PLAINS. ALSO...THE INCREASING PRESSURE GRADIENT CONTINUES TO CAUSE A STRENGTHENING TREND IN EASTERLY TRADES ACROSS THE CARIBBEAN BASIN AND SW N ATLC THROUGH THIS WEEK. THE STRONGEST OF THESE WINDS ARE NEAR THE COAST OF COLOMBIA...WHERE THE 28/2300 UTC HIGH-RESOLUTION QUIKSCAT PASS DEPICTS WINDS TO 35 KT. THUS...A GALE WARNING HAS BEEN POSTED 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 RESULTING IN A LOCAL ENHANCEMENT. THESE TRADES WILL MAINTAIN 8 TO 10 FT SEAS ACROSS A LARGE PART OF THE CARIBBEAN AND SW N ATLC...WITH SEAS TO 13 FT NEAR THE COAST OF COLOMBIA. THE MAIN FORECAST CHALLENGE ARRIVES TUESDAY NIGHT...AS THE AFOREMENTIONED UPPER LEVEL TROUGH TRANSLATES EASTWARD AND BECOMES IN PHASE WITH A SEPARATE UPPER TROUGH OVER THE MIDWEST. CURRENTLY...AN ELONGATED FRONTAL ZONE IS DRAPED ACROSS THE SOUTHERN PLAINS AND SE CONUS. WHEN THE ATMOSPHERIC LIFT ASSOCIATED WITH THE UPPER TROUGH CATCHES UP TO THE FRONTAL ZONE...OPERATIONAL MODELS SPIN UP A SURFACE LOW ON THE FRONT. COLD AIR ADVECTION WEST OF THE INCIPIENT LOW WILL FORCE THE FRONT SOUTHWARD AS A COLD FRONT. THIS FRONT IS FORECAST TO ENTER THE NW GULF TUESDAY NIGHT. SOME INCONSISTENCY STILL EXISTS AMONG OPERATIONAL MODELS...WITH THE NAM BEING THE MOST PROGRESSIVE COMPARED TO THE ECMWF AND GFS. STILL FEEL THE NAM HAS THE BEST HANDLE ON THE COLD FRONT MOTION...GIVEN THE CLIMATOLOGICALLY FAST SOUTHWARD SURGES OF COLD FRONTS OVER THE W GULF WITH RELATIVELY STRONG SURFACE HIGHS TO THE NW. IN FACT...RECENT RUNS OF OTHER OPERATIONAL MODELS ARE NOW COMING IN LINE WITH THE NAM THAT SAID...EXPECT THE FRONT MOVING OFF THE SE TEXAS COAST AROUND 04Z WED...WITH THE WESTERN PORTION OF THE FRONT SURGING SOUTH OF THE INTERNATIONAL BORDER BY 09Z WED. THEREAFTER...THE FRONT IS FORECAST TO BECOME TEMPORARILY STATIONARY FROM VERACRUZ TO THE FLORIDA BIG BEND. 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 LARGE-SCALE 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 A DEVELOPING WEST CONUS COAST RIDGE...GFS AND ECMWF MOVE THE SURFACE HIGH SOUTHEASTWARD OVER THE NW GULF...CAUSING THE PRE-EXISTING FRONT TO SURGE SOUTHEASTWARD ON FRIDAY AND SATURDAY. ECMWF IS SLIGHTLY LESS AGGRESSIVE WITH THE SOUTHEASTWARD SURGE. HOWEVER...GIVEN GOOD CONSISTENCY AMONG GFS ENSEMBLES IN THE STRENGTH AND INTENSITY OF THE SURFACE HIGH OVER TEXAS...WENT WITH THE STRONGER SURFACE HIGH AND STRONGER FRONTAL PUSH ACROSS THE GULF. 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 MEMBERS OF THE GFS HAVE BACKED OFF A BIT ON THE MAXIMUM INTENSITY OF THESE WINDS. THIS IS LIKELY THE CASE AS THE UPPER TROUGH TRANSITIONS FROM POSITIVELY- TO NEGATIVELY-TILTED LATE THIS WEEK THUS DRAGGING THE UPSTREAM SUBSIDENCE AND SURFACE HIGH NORTHEASTWARD AND AWAY FROM THE GULF OF MEXICO. HOWEVER... MODULATIONS TO THE SURFACE FLOW DUE TO PRESENCE HIGHER TERRAIN OVER MEXICO WILL LIKELY RESULT IN GALE FORCE WINDS ACROSS THAT PORTION OF THE W GULF AND BAY OF CAMPECHE FRIDAY CLOSEST TO THE MEXICO COAST. THIS SAME FRONT WILL MOVE OFF THE SE CONUS INTO THE W ATLC ON FRIDAY...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...AND SUGGESTS WINDS UNDER GALE FORCE. HELD OFF ON ANY GALE IN THIS REGION WITH THE EXISTING UNCERTAINTY. WAVE HEIGHTS IN THE WAKE OF THE FRONT WILL INCREASE TO AS HIGH AS 12 FT OVER THE W GULF AND 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 THROUGH TONIGHT. GULF OF MEXICO... NONE. FORECASTER COHEN. TROPICAL PREDICTION CENTER.