000 AGXX40 KNHC 210659 MIMATS MARINE WEATHER DISCUSSION NWS NATIONAL HURRICANE CENTER MIAMI FL 300 AM EDT FRI SEP 21 2012 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... THE DISSIPATING FRONTAL BOUNDARY IN THE GULF HAS LEFT BEHIND A SURFACE TROUGH OVER THE WESTERN GULF EVIDENT ON ASCAT IMAGERY FROM 0012 UTC. THIS TROUGH IS EXPECTED TO LINGER OVER THE WESTERN GULF THROUGH SAT MORNING BEFORE DISSIPATING. A TROPICAL WAVE WILL PASS THROUGH THE GULF S OF 23N THIS EVENING THROUGH TUE. A WEAK COLD FRONT WILL DIP INTO THE FAR NE GULF ON SUN AND LINGER OVER THE NORTHERN GULF INTO MON BEFORE GRADUALLY DISSIPATING TUE INTO WED. SEAS IN THE GULF WILL REMAIN 4 FT OR LESS UNTIL THE INTRUSION OF THIS COLD FRONT ON SUN. THE BUILDING PRES GRADIENT BETWEEN HIGH PRES BEHIND THE COLD FRONT AND LOWER PRES OVER THE SW GULF NEAR THE TROPICAL WAVE WILL INCREASE WINDS TO A FRESH BREEZE AND SEAS TO 4-6 FT PRIMARILY OVER THE CENTRAL GULF SUN AND MON BEFORE THE GRADIENT RELAXES. THE MODELS ARE IN REASONABLE AGREEMENT ON THE TIMING AND STRENGTH OF THIS FRONT AS WELL AS THE OTHER FEATURES. A BLEND OF THE 00Z GFS AND ECMWF WILL BE USED TO ADJUST THE FORECAST. SOUTHWEST NORTH ATLC S OF 31N W OF 55W... A SURFACE TROUGH IS EXPECTED TO LINGER BETWEEN SOUTHEAST FLORIDA AND THE BAHAMAS TODAY INTO SAT. ITS ORIGINS ARE PARTLY FROM THE DISSIPATING SURFACE BOUNDARY CURRENTLY OVER CENTRAL FLORIDA AND THE NORTHERN PORTION OF THE TROPICAL WAVE PASSING THROUGH THE NW CARIBBEAN. THIS TROUGH WILL BE A FOCUS FOR CONVECTION. A COLD FRONT WILL MOVE THROUGH NE FLORIDA AND INTO NW WATERS BY SUN EVENING. THE FRONT WILL DRAW THIS TROUGH NORTHWARD. AS HIGH PRES MOVES IN BEHIND THE FRONT...THE PRES GRADIENT WILL INCREASE OVER NW WATERS...WITH WINDS BRIEFLY REACHING A FRESH BREEZE MON EVENING. A TROPICAL WAVE MOVING THROUGH THE NE CARIBBEAN THIS MORNING WILL MOVE INTO WATERS W OF 65W BY SUN AND PASS S OF THE BAHAMAS THROUGH WED ON ITS WAY TOWARD THE STRAITS OF FLORIDA. THIS WAVE WILL SUPPLY MORE MOISTURE TO THE WEAKENING COLD FRONT OVER CENTRAL OR SOUTHERN FLORIDA BY TUE. OTHERWISE...THE MAIN CONCERN LIES OVER FAR NE WATERS WHERE AN AREA OF LOW PRES NEAR 32N56W IS GENERATING FRESH TO STRONG SE TO S WINDS ON ITS SE SIDE OVER FORECAST WATERS N OF 29N ACCORDING TO THE 0004 UTC ASCAT PASS AS WELL AS SEAS TO 10 FT. THIS LOW IS FORECAST TO SLOWLY MOVE NW AWAY FROM THE FORECAST AREA. WINDS AND SEAS SHOULD SUBSIDE BELOW ADVISORY CRITERIA BY SAT AFTERNOON. THE MODELS ARE IN GOOD AGREEMENT WITH THIS LOW UNTIL SAT MORNING WHEN THE GFS BECOMES WEAKER THAN THE ECMWF...CMC...AND NOGAPS. PREFER TO HOLD ON TO THIS PERSISTENT LOW A BIT LONGER...SO THE FORECAST WILL BE ADJUSTED TOWARD THE 00Z ECMWF HERE. THE MODELS ARE IN REASONABLE AGREEMENT WITH THE OTHER FEATURES. A BLEND OF THE PREVIOUS FORECAST WITH THE 00Z GFS AND ECMWF SHOULD ACCOMMODATE THE SMALL UNCERTAINTY DUE TO MODEL SPREAD ELSEWHERE. CARIBBEAN SEA AND TROPICAL N ATLC W OF 55W... THE TROPICAL WAVE IN THE NW CARIBBEAN ALONG 84W WILL BE A FOCUS FOR CONVECTION AS IT TRAVELS W INTO THE YUCATAN BY SUN. HIGH PRES WILL BRIEFLY BUILD OVER THE SE U.S. AHEAD OF THE AFOREMENTIONED COLD FRONT MOVING INTO THE NE GULF AND OVER NORTHERN FLORIDA BY SUN EVENING...BUILDING THE PRES GRADIENT OVER THE CARIBBEAN. FRESH TO STRONG E WINDS ARE EXPECTED ALONG THE COAST OF COLOMBIA BEGINNING SAT MORNING. THIS SURFACE RIDGING WILL BE REPLACED BY STRONGER HIGH PRES NW OF THE COLD FRONT BY SUN THAT WILL WEAKEN BY MON NIGHT...DIMINISHING THE PRES GRADIENT AS WELL AS THE WINDS AND SEAS ALONG THE COAST OF COLOMBIA. THIS IS THE ONLY SPOT IN THE CARIBBEAN WHERE ADVISORY CONDITIONS WILL BE MET THROUGH WED. A SECOND TROPICAL WAVE CURRENTLY OVER THE NE CARIBBEAN WILL ENCOUNTER SELY STEERING FLOW AND MOVE W-NW NEXT COUPLE OF DAYS. IT IS DIFFICULT TO FOLLOW IN THE MODEL GUIDANCE BY THE WEEKEND AS A MID LEVEL DEFORMATION ZONE SETS UP N OF PR/USVI REGION. OTHER THAN CONVECTION OCCURRING WITH THE INTERACTION OF THIS WAVE AND MID ATLC TROUGH...NO SIGNIFICANT EFFECTS IN WINDS AND SEAS ARE EXPECTED WITH THIS WAVE. A THIRD TROPICAL WAVE WILL REACH THE TROPICAL N ATLC WATERS SUN NIGHT....ACCOMPANIED BY A BROAD LOW LEVEL WIND SURGE AND 8-9 FT SEAS. THERE ARE NO NOTABLE MODEL DIFFERENCES...SO A BLEND OF THE LATEST GFS AND ECMWF WILL BE USED TO UPDATE THE FORECAST. NOTE...GRIDDED MARINE FORECAST IS AVAILABLE AT WWW.NHC.NOAA.GOV/TAFB/GRIDDED_MARINE GULF OF MEXICO... .NONE. CARIBBEAN SEA AND TROPICAL N ATLC... .NONE. SW N ATLANTIC... .NONE. FOR ADDITIONAL INFORMATION PLEASE VISIT WWW.HURRICANES.GOV/MARINE $$ FORECASTER SCHAUER