000 AGXX40 KNHC 171854 MIMATS MARINE WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 255 PM EDT FRI APR 17 2009 MARINE WEATHER DISCUSSION FOR GULF OF MEXICO...CARIBBEAN SEA AND SOUTHWEST NORTH ATLC S OF 31N W OF 55W. GULF OF MEXICO... A WARM FRONT CONTINUES LIFTING NORTHWARD ACROSS THE GULF REGION...WITH SCATTERED SHOWERS AND THUNDERSTORMS CONTINUING TO SLIDE SOUTHEASTWARD ALONG THE FRONT. THIS FRONT IS BEING DRIVEN NORTHWARD BY THE RETURN FLOW AROUND A BROAD SURFACE RIDGE OVER THE E CONUS. THIS RETURN FLOW IS ALSO BEING MAINTAINED BY A SURFACE HIGH DRIFTING SOUTHEASTWARD FROM THE GREAT LAKES REGION...AND IS FORECAST TO REACH N GEORGIA BY SAT MORNING. THE QUIKSCAT PASS AROUND 17/1200 UTC INDICATES SE WINDS OF 20 TO 25 KT ACROSS A LARGE PART OF THE GULF...WITH THE STRONGEST WINDS ACROSS THE NW GULF. SHIPS ARE REPORTING UP TO 9 FT SEAS IN THIS REGION...DUE TO THE LONG FETCH LENGTH...WHICH ARE A FOOT OR TWO ABOVE WAVEWATCH GUIDANCE. THE AREA OF 8 TO 9 FT SEAS WILL SPREAD ACROSS A LARGE PORTION OF THE WESTERN GULF THROUGH SATURDAY. THE AFOREMENTIONED SURFACE RIDGE IS ASSOCIATED WITH A DEEP LAYER RIDGE OVER THE E CONUS...AND THE MAIN PROBLEM OF THE FORECAST PERIOD IS HOW THIS RIDGE WILL BREAK DOWN AS A MID/UPPER-LEVEL LOW OVER THE SOUTHERN ROCKIES IS EJECTED EASTWARD AS AN OPEN TROUGH THIS WEEKEND. THE SPREAD AMONG MODEL GUIDANCE CONTINUES TO NARROW...WITH GENERAL AGREEMENT ON A GRADUAL BREAK DOWN OF THE E CONUS RIDGE THROUGH THE WEEKEND. THE MID/UPPER-LEVEL TROUGH WILL BE EJECTED EASTWARD INTO THE OHIO VALLEY REGION BY SUNDAY...WITH A RELATIVELY WEAK FRONT ENTERING THE NW GULF EARLY SUNDAY AFTERNOON. THE FRONT WILL BE INITIALLY FOLLOWED BY N WINDS OF 15 TO 20 KT...HIGHEST ALONG THE COAST OF MEXICO. MEANWHILE...A VIGOROUS SHORTWAVE TROUGH CURRENTLY OVER THE PACIFIC NORTHWEST WILL DIVE SOUTHEASTWARD INTO THE UPPER MIDWEST THROUGH SUNDAY...AS A STRONG UPPER LEVEL JET STREAK UPSTREAM OF THE TROUGH AXIS FORCES THE TROUGH TO DIG SOUTHWARD. THIS WILL RESULT IN THE NORTHWESTERN TROUGH BECOMING IN PHASE WITH THE AFOREMENTIONED TROUGH OVER THE OHIO VALLEY REGION...CARVING OUT A DEEP LONGWAVE TROUGH OVER THE E CONUS BY MONDAY...WITH A HIGH AMPLITUDE LONGWAVE UPPER RIDGE OVER THE WESTERN CONUS. STRONG SUBSIDENCE E OF THIS RIDGE WILL RESULT IN SURFACE PRESSURE RISES OVER S TEXAS AND E MEXICO MON AND TUE...WITH THE FRONT BECOMING REINFORCED DURING THIS TIME. NORTHERLY WINDS IN THE WAKE OF THE FRONT WILL INCREASE BY LATE MON INTO TUE...WITH THE FRONT CLEARING THE GULF BY LATE TUE. N WINDS OF 20 TO 25 KT WILL AFFECT A LARGE PART OF THE W GULF IN THE WAKE OF THE SECONDARY SURGE LATE MON AND TUE...THOUGH THERE IS INCREASING CONCERN FOR STRONGER WINDS IN THE SW GULF...WHERE THE NEARBY TOPOGRAPHY IN MEXICO WILL ACT TO FUNNEL THE COLDER AIR SOUTHWARD. OPERATIONAL MODELS ARE INDICATING A RATHER STRONG SURFACE RIDGE IN THE WAKE OF THE FRONT...WITH THE OPERATIONAL GFS INDICATING A LOW THREAT FOR MINIMAL GALE FORCE WINDS S OF 22N W OF 93W. THE AIRMASS IN THE WAKE OF THE FRONT IS NOT PARTICULARLY COLD WHERE THE LOW LEVEL JET STRENGTH IS NOT EXPECTED TO EXCEED 34 KT. THESE FACTORS WILL LIKELY LIMIT THE POTENTIAL FOR STRONG LOW LEVEL MIXING AFTER THE SECONDARY SURGE. THUS...FORECAST NORTHERLY WINDS HAVE BEEN INCREASED TO 30 KT FOR LATE MON INTO TUE S OF 22N W OF 93W...AND THE THREAT FOR GALES WILL CONTINUE TO BE MONITORED IN THIS REGION. THE STRONGER POST FRONTAL WINDS WILL RAISE SEAS BACK TO 8 FT OVER THE W GULF AFTER A BRIEF LULL PRIOR TO FRONTAL PASSAGE. SW N ATLC... A COLD FRONT EXTENDS FROM 31N58W TO NE CUBA...WITH A REINFORCING FRONT EXTENDING FROM A SURFACE LOW N OF THE AREA TO 31N65W TO 28N70W TO 28N78W. MODEL GUIDANCE AND RECENT SCATTEROMETER DATA DATA INDICATE SW WINDS OF 20 TO 30 KT E OF THE INITIAL FRONT N OF 27N...WITH W TO NW WINDS AROUND 20 KT W OF THE INITIAL FRONT...AND N TO NE WINDS OF 20 TO 25 KT N OF THE REINFORCING FRONT. THE SURFACE LOW IS FORECAST TO MOVE SOUTHEASTWARD DURING THE NEXT DAY...WITH THE REINFORCING FRONT BECOMING THE DOMINANT FRONT BY EARLY SUN. SW WINDS E OF OF THIS FRONT WILL BE IN THE 20 TO 25 KT RANGE AS IT MOVES EASTWARD THROUGH SUN AND WEAKENS WHILE ENCOUNTERING A STRONGER SURFACE RIDGE OVER THE E ATLC. WAVE HEIGHTS UP TO 15 FT IN NE SWELL IN THE WAKE OF THE REINFORCING FRONT WILL IMPACT MUCH OF THE SW NORTH ATLC SAT AND SUN WITH MAXIMUM SEA HEIGHTS SUBSIDING BY LATE SUN. IN THE WAKE OF THIS REINFORCING FRONT...SURFACE HIGH PRESSURE WILL BUILD OVER THE SW NORTH ATLC. THE NEXT FRONT...DISCUSSED IN THE GULF OF MEXICO SECTION ABOVE...WILL MOVE OFF THE SE GEORGIA COAST TUESDAY. SW WINDS OF 20 TO 25 WILL DEVELOP AHEAD OF THIS FRONT ACROSS THE W ATLC ON MONDAY. CARIBBEAN AND TROPICAL N ATLC... FRESH TRADE WINDS ARE FORECAST TO CONTINUE ACROSS THE REGION THROUGH EARLY NEXT WEAK...AS A RESULT OF PERSISTENT AND BROAD SURFACE RIDGING N OF THE DISCUSSION AREA. PERIODIC WEAKNESSES IN THIS RIDGING DUE TO FRONTAL PASSAGES N OF THE CARIBBEAN WILL KEEP THESE TRADES NEAR OR SLIGHTLY BELOW SEASONAL AVERAGES. THE LATEST SCATTEROMETER AND SURFACE OBSERVATIONS INDICATE NE TO E WINDS OF 20 TO 25 KT ACROSS THE CARIBBEAN...HIGHEST NEAR THE COAST OF COLOMBIA AND THE GULF OF HONDURAS. THIS WEEKEND... SURFACE HIGH PRESSURE WILL BUILD OVER THE SE CONUS RESULTING IN AN INCREASE IN N WINDS THROUGH THE WINDWARD PASSAGE. ALSO...LONG PERIOD NORTHERLY SWELL IS FORECAST TO SPREAD THROUGH THE E CARIBBEAN PASSAGES THIS WEEKEND. EARLY NEXT WEEK...TRADES WILL INCREASE OVER THE E CARIBBEAN AND TROPICAL N ATLC AS SURFACE HIGH PRESSURE BUILDS OVER THE CENTRAL ATLC...THOUGH THEY WILL DECREASE OVER THE W CARIBBEAN WITH THE APPROACH OF THE GULF OF MEXICO COLD FRONT. ATLC... .NONE.. CARIBBEAN... .NONE. GULF OF MEXICO... .NONE. FORECASTER COHEN. TROPICAL PREDICTION CENTER.