000 AGXX40 KNHC 201748 MIMATS MARINE WEATHER DISCUSSION NWS NATIONAL HURRICANE CENTER MIAMI FL 150 PM EDT SAT OCT 20 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... AS OF 12Z...THE COLD FRONT OVER THE GULF STRETCHES FROM NEAR VENICE FLORIDA TO 24N89W. THE WESTERN PART OF THE FRONT HAS DISSIPATED THIS MORNING WHILE THE EASTERN PORTION WILL MOVE OUT OF THE AREA LATER TODAY. A HIGH PRES RIDGE WILL BUILD BEHIND THE FRONT WITH WINDS BECOMING FRESH OVER MUCH OF THE GULF SUN NIGHT INTO TUE. UNCERTAINTY COMES INTO THE FORECAST ON TUE WHEN THE PATTERN IN THE GULF BECOMES DEPENDENT ON THE EVOLUTION OF THE SYSTEM IN THE SW CARIBBEAN SEA. PLEASE SEE THE CARIBBEAN SEA SECTION BELOW FOR DETAILS. THE PRES GRADIENT IS EXPECTED TO RELAX OVER THE WESTERN GULF AND BUILD OVER THE EASTERN GULF BETWEEN HIGH PRES OVER THE SOUTHERN APPALACHIAN MOUNTAINS AND DEEPENING LOW PRES EXPECTED TO LIFT NORTHWARD THROUGH THE WESTERN CARIBBEAN TOWARD JAMAICA. THE MODELS AGREE ON THIS GENERAL PATTERN. THE 12Z GFS FORECAST APPEARS REASONABLE FOR THE MAJORITY OF THE PERIOD...BUT DIFFERS FROM THE MEDIUM RANGE POINTS AGREED TO DURING THE NHC/HPC COORDINATION CALL FOR THE SYSTEM IN THE CARIBBEAN. HEDGED TOWARD THE 00Z ECMWF WED ONWARD BECAUSE IT MORE CLOSELY RESEMBLED THOSE AGREED UPON POINTS. SW N ATLC S OF 31N W OF 65W... THE COLD FRONT FROM 31N74W TO SEBASTIAN INLET FLORIDA WILL CONTINUE TO WEAKEN AS IT MOVES EASTWARD...REACHING AS FAR S AS THE CENTRAL BAHAMAS SUN BEFORE MOVING E OF THE AREA MON NIGHT. HIGH PRES WILL BUILD BEHIND THE FRONT SUN NIGHT THROUGH TUE...WITH WINDS BECOMING FRESH W OF 76W SUN NIGHT AND ACROSS MUCH OF THE SW N ATLC BY MON NIGHT. CONFIDENCE DIMINISHES BEGINNING MON NIGHT AS THE PRES GRADIENT BUILDS BETWEEN HIGH PRES ANCHORED OVER THE SOUTHERN APPALACHIAN MOUNTAINS AND DEVELOPING LOW PRES IN THE SW CARIBBEAN. SEE THE SECTION BELOW FOR DETAILS ON THE CARIBBEAN SYSTEM. THE MODELS GENERALLY AGREE ON LIFTING A LOW PRES SYSTEM NORTHWARD IN THE WESTERN CARIBBEAN TOWARD JAMAICA TUE AND WED. LIKE IN THE GULF...THE 12Z GFS SEEMS REASONABLE FOR THE MAJORITY OF THE FORECAST PERIOD. THE GRIDDED FORECAST WAS ADJUSTED TOWARD THE 00Z ECMWF WED ONWARD...HOWEVER. THE 00Z ECMWF MORE CLOSELY RESEMBLES THE NHC/HPC COORDINATED SCENARIO FOR THE LOW PRES SYSTEM LIFTING NORTHWARD THROUGH THE WESTERN CARIBBEAN. HOWEVER...DID NOT RAISE WINDS ABOVE THE 25 KT THRESHOLD NEAR THE END OF THE GRIDDED FORECAST PERIOD JUST YET GIVEN THE UNCERTAINTY IN THE FORECAST. CARIBBEAN SEA AND TROPICAL N ATLC W OF 55W... THE TROPICAL WAVE ALONG 72W WILL GRADUALLY MOVE W THROUGH THE CENTRAL CARIBBEAN THROUGH THE REMAINDER OF THE WEEKEND AND MERGE WITH THE MONSOONAL TROUGH THAT STRETCHES FROM THE E PACIFIC INTO THE SW CARIBBEAN. ON MON...UPPER DIFFLUENCE ASSOCIATED WITH THE THE REAR RIGHT QUADRANT OF THE SOUTHERN STREAM UPPER JET THAT IS FORECAST TO SPLINTER AWAY FROM THE DEEP LAYER TROUGH CURRENTLY OVER THE GULF OF MEXICO WILL ENHANCE CONVECTION OVER THE MOISTURE RICH SW CARIBBEAN. THE MODELS AGREE ON DEVELOPING AN AREA OF LOW PRES IN THIS AREA AND GRADUALLY DEEPENING IT AS IT LIFTS NORTHWARD TOWARD JAMAICA...POSSIBLY AS A TROPICAL CYCLONE...MON NIGHT THROUGH WED. THE 12Z GFS HAS TRENDED MORE TO THE W WITH THE LOW TRACK TUE-THU. THIS IS MORE IN LINE WITH THE MODEL CONSENSUS AND THE NHC/HPC MEDIUM RANGE COORDINATED POINT FOR THE SYSTEM. HOWEVER...IT IS NOT THE MODEL CLOSEST TO THE COORDINATED FORECAST. THAT HONOR GOES TO THE 00Z ECMWF. ITS FORECAST WAS USED TO ADJUST THE GRIDS FROM TUE ONWARD. WINDS WERE CAPPED AT 30 KT FOR NOW GIVEN THE UNCERTAINTY IN THE FORECAST AND THE LACK OF A CLEAR CIRCULATION AT THE PRESENT TIME. 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