000 AGXX40 KNHC 270718 MIMATS MARINE WEATHER DISCUSSION NWS NATIONAL HURRICANE CENTER MIAMI FL 320 AM EDT THU SEP 27 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... FAIRLY TRANQUIL CONDITIONS WITH WINDS AND SEAS BELOW ADVISORY THRESHOLDS WILL PREVAIL THROUGH FRI. MORE UNCERTAINTY COMES INTO THE FORECAST FOR THE WEEKEND WHEN A COLD FRONT IS EXPECTED TO MOVE OFF THE TEXAS COAST FORCED BY A COMPLEX COMBINATION OF A COMPACT UPPER LOW CURRENTLY OVER WRN COLORADO...A WEAK TROUGH TO ITS SW...AND ONE OF MORE IMPULSES STREAMING NEWD FROM E PACIFIC T.S. MIRIAM INTO THE SOUTHERN PLAINS. CONSIDERING THE COMPLEX SCENARIO...THE MODELS SHOW REASONABLY GOOD AGREEMENT ON THE GENERAL PATTERN WHICH SPORTS A COLD FRONT SLOWLY PASSING THROUGH THE WESTERN HALF OF THE GULF WITH LOW PRES TRACKING ALONG THE FRONT THROUGH THE NORTHERN GULF. THE 00Z ECMWF IS SLIGHTLY WEAKER WITH THE SFC WAVE AND FASTER CARRYING THE FRONT EASTWARD THAN ITS 12Z RUN UNTIL 18Z MON AND THEN THE 00Z RUN COMES INTO BETTER AGREEMENT WITH THE 12Z RUN ON THE TIMING OF THE FRONT. THE GFS APPEARS TO BE CONVERGING ON A SOLUTION FOR THE FRONTAL TIMING...WITH THE 00Z RUN SLOWER THAN THE 18Z RUN BUT FASTER THAN THE 12Z RUN. THE 00Z ECMWF IS SLIGHTLY WEAKER AND MORE NELY WITH THE SURFACE LOW TRACK AND CARRIES THE FRONT EWD FASTER THAN THE 00Z GFS...BUT THE DIFFERENCES IN THE STRENGTH OF THEIR WIND FIELDS ARE SMALL WITH WINDS BARELY REACHING ADVISORY CRITERIA. BLENDING THE GFS AND ECMWF WAS THE RECOMMENDATION OF THE EARLIER MODEL DIAGNOSTIC DISCUSSION FROM HPC...AND THIS STILL SEEMS LIKE THE BEST IDEA GIVEN THE UNCERTAINTIES IN THIS COMPLEX PATTERN. SOUTHWEST NORTH ATLC S OF 31N W OF 55W... WINDS AND SEAS WILL REMAIN BELOW ADVISORY CRITERIA FOR THE ENTIRE FORECAST PERIOD. THE 00Z GFS CONTINUES TO BACK OFF ON THE SOUTHERLY WINDS ALONG 70W WITHIN THE AREA OF A TIGHT PRES GRADIENT BETWEEN THE BUILDING HIGH PRES IN THE CENTRAL ATLC AND THE FRONT APPROACHING FROM THE CENTRAL U.S./GULF OF MEXICO. A BLEND OF THE GFS AND ECMWF APPEARS TO BE BEST FOR ADJUSTING THE FORECAST BOTH HERE AND WITH THE FRONTAL BOUNDARY AS IT APPROACHES THE N FL COAST. THE LATEST RUNS HANG UP THE BOUNDARY W OF THE SW N ATLC BY THE END OF THE FORECAST PERIOD. CHANGES WILL BE MADE TO KEEP THE FRONT OUT OF THE SW N ATLC ZONE PER THE 00Z GFS/ECMWF WHEN UPDATING THE FORECAST. CARIBBEAN SEA AND TROPICAL N ATLC W OF 55W... THE TROPICAL WAVE OVER THE CENTRAL CARIBBEAN HAS LOST MOST OF ITS CONVECTION AS IT HAS MOVED W OF THE UPPER TROUGH AXIS INTO A REGION OF MORE CONFLUENT FLOW ALOFT. THE 0256 UTC ASCAT PASS SHOWS WINDS HAVE DIMINISHED BELOW A STRONG BREEZE EXCEPT WITHIN 30 NM OF THE COAST OF COLOMBIA WITH SHIP A8JH8 REPORTING 19 KT NEAR 12N73W AT 0300 UTC. THE 00Z GFS IS BEST INITIALIZED WITH THE WIND FIELD HERE BUT ITS WW3 IS TOO HIGH WITH THE ELY SWELL PROPAGATING INTO THE WESTERN CARIBBEAN. IT SHOWS 6-7 FT WHERE NEAR 14N78W WHERE SHIP A8JR6 REPORTED 5 FT AT 06Z. ADJUSTMENTS WILL BE MADE TO THE FORECAST TO BRING THE SWELL DOWN A BIT FASTER THAN THE WW3. TRADES REMAIN WEAK THU AND FRI AS THE DRIVING HIGH PRES TO THE N WEAKENS. OVER THE WEEKEND...HIGH PRES IS EXPECTED TO BUILD IN THE CENTRAL ATLC AND FORCE A TIGHTER PRES GRADIENT OVER THE CENTRAL CARIBBEAN BETWEEN THE RIDGING AND TROUGHING OVER SOUTH AMERICA AS WELL AS OVER THE GULF OF MEXICO. THE 00Z GFS IS STRONGER THAN THE ECMWF...SHOWING A MORE EXPANSIVE REGION OF 20-25 KT WINDS. WITH A GFS/ECMWF PREFERRED WITH THE FRONT TO THE W AND THESE MODELS IN REASONABLE AGREEMENT ON THE STRENGTH OF THE RIDGE...THINK A BLEND IS APPROPRIATE TO ADJUST THE FORECAST HERE AS WELL. 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