000 AGXX40 KNHC 201850 MIMATS MARINE WEATHER DISCUSSION NWS NATIONAL HURRICANE CENTER MIAMI FL 300 PM EDT WED JUN 20 2012 MARINE WEATHER DISCUSSION FOR THE GULF OF MEXICO...CARIBBEAN SEA AND SOUTHWEST NORTH ATLC S OF 31N W OF 55W. GULF OF MEXICO... THERE CONTINUES TO BE CONSIDERABLE UNCERTAINTY WITH THE EVOLUTION OF THE TROUGH MOVING N OUT OF THE NW CARIBBEAN THIS AFTERNOON. THE 12Z GFS HAS CONSIDERABLE GRID-SCALE FEEDBACK ISSUES AT SEVERAL POINTS IN ITS SEVEN DAY FORECAST...THE MOST EGREGIOUS OF THESE COMES AROUND FHR 84-102 WHERE THE GFS STAMPS OUT BETWEEN 2.73-4.19 INCHES OF PRECIPITATION OVER 6 HOUR PERIODS IN THE NE GULF...ONLY 0.82-1.39 INCHES OF WHICH IS CONVECTIVE. THE GFS RAPIDLY DEEPENS A LOW PRES SYSTEM ASSOCIATED WITH THIS FEEDBACK ALONG THE LOW LEVEL TROUGH OVER THE EASTERN GULF. THE 12Z RUN NOW DEVELOPS THIS LOW FARTHER W THAN THE 06Z RUN WHICH HAD CARRIED A 1002 MB LOW JUST N OF FT MYERS BY ITS 96 HOUR FORECAST THAT CONTINUED NE ACROSS FL AND RAPIDLY DEEPENED INTO A GALE LOW IN THE ATLC BY SUN AFTERNOON. THE 12Z GFS IS IN BETTER AGREEMENT WITH THE 00Z/19 ECMWF AND THE 12Z GEFS MEAN BY HOLDING THE LOW FARTHER W. A COMPROMISE BETWEEN THE NHC AND HPC MEDR POINTS FROM THE 1 PM EDT CONFERENCE CALL SUGGESTED A PSN NEAR 26.5N87W SUN MORNING. THIS POINT IS CLOSE TO THE 12Z GFS SOLUTION AS WELL AS THE 12Z GEFS MEAN AND 00Z/19 ECMWF ENSEMBLE MEAN POSITIONS. GIVEN THE UNCERTAINTY IN THE FORECAST...AN ENSEMBLE MEAN SEEMS TO BE THE WAY TO GO FOR THE TIME BEING. THE 12Z GEFS MEAN CARRIES 25 KT WINDS IN THE STRAITS OF FL WHICH ARE VERIFYING WELL. THESE STRONG WINDS DIMINISH TO FRESH IN THE GEFS BY THU MORNING AND DO NOT RETURN AS THE WIND FIELD EXPANDS. THIS APPEARS TO BE A COMPROMISE BETWEEN THE FEEDBACK-RIDDLED GFS AND THE 12Z ECMWF. CARIBBEAN SEA AND TROPICAL N ATLC W OF 55W... CONVECTION CONTINUES OVER THE NW CARIBBEAN...WITH THE CENTROID PSN LOCATED JUST S OF WESTERN CUBA. THIS CONVECTION IS AIDED IN PART BY DIVERGENCE ALOFT ON THE SE SIDE OF AN UPPER TROUGH CURRENTLY EXTENDING FROM THE N CENTRAL GULF OF MEXICO TO WESTERN CUBA. FRESH LOW LEVEL SOUTHERLY FLOW IS PUMPING MOISTURE TOWARD THE SURFACE TROUGH STRETCHED FROM THE WESTERN TIP OF CUBA INTO THE SE GULF OF MEXICO. THIS MOISTURE WILL MIGRATE ACROSS WESTERN CUBA AND INTO THE FAR SE GULF THROUGH THU AND THE SOUTHERLY FLOW WILL WEAKEN. FARTHER EAST...FRESH TRADE WINDS ARE OVER PRIMARILY THE EASTERN AND CENTRAL CARIBBEAN IN ADVANCE OF A TROPICAL WAVE ALONG 64W. RECENT OBSERVATION SHOW THE WINDS AND SEAS ARE BEGINNING TO DIMINISH AS THE SUBTROPICAL RIDGE N OF THE AREA WEAKENS. THE TROPICAL WAVE WILL MOVE THROUGH THE CENTRAL CARIBBEAN AND THEN WILL BECOME DIFFUSE AS IT ENTERS THE W CARIBBEAN AND INTERACTS WITH THE MONSOON TROUGH FRI. WINDS OVER THE CARIBBEAN WILL HINGE ON THE EVOLUTION OF THE SUBTROPICAL RIDGE TO THE N WHICH WILL BE HIGHLY DEPENDENT ON THE FORECAST FOR THE LOW IN THE GULF OF MEXICO. THE GEFS MEAN IS PREFERRED WHICH WILL KEEP MODERATE TO FRESH WINDS OVER MUCH OF THE CARIBBEAN THROUGH SUN. A SECOND TROPICAL WAVE WELL E OF THE AREA WILL PUSH WEST OF 55W BY SUN. SOUTHWEST NORTH ATLC S OF 31N W OF 55W... A TROUGH LIES FROM 31N65W TO THE N BAHAMAS. THE 1432 UTC ASCAT PASS SHOWS AN AREA OF 15 TO 20 KT WINDS JUST N OF THE BAHAMAS W OF 75W...BETWEEN THE TROUGH AND SURFACE HIGH CENTERED OFF THE CAROLINAS. THESE WINDS SHOULD DIMINISH TONIGHT AS THE TROUGH PULLS EASTWARD AND HIGH PRES MOVES SE...APPROACHING NE WATERS. THERE ARE LARGE CHANGES IN THE GFS FORECAST IN THE LONGER RANGES. THE 06Z RUN HAD A LOW PRES SYSTEM MOVING ACROSS FL AND DEVELOPING INTO A GALE LOW IN THE ATLC BY SUN AFTERNOON. THE 12Z RUN HAS ABANDONED THIS IDEA...KEEPING THE LOW IN THE GULF LONGER AND NEVER GENERATING WINDS STRONGER THAN 25 KT IN THE SW N ATLC THROUGH SUN NIGHT. AS EXPLAINED IN THE GULF OF MEXICO SECTION...THE GRIDS WERE ADJUSTED TOWARD THE 12Z GEFS MEAN. THIS SHOULD KEEP HIGH PRES NEAR NE WATERS AND WINDS LIGHT TO MODERATE OVER MUCH OF THE SW N ATLC. NOTE...GRIDDED MARINE OUTPUT IS AVAILABLE AT WWW.NHC.NOAA.GOV/TAFB/GRIDDED_MARINE (LOWER CASE) GULF OF MEXICO... .NONE. CARIBBEAN SEA... .NONE. SW N ATLANTIC... .NONE. FOR ADDITIONAL INFORMATION PLEASE VISIT WWW.HURRICANES.GOV/MARINE $$ FORECASTER SCHAUER