000 AGXX40 KNHC 200659 MIMATS MARINE WEATHER DISCUSSION NWS NATIONAL HURRICANE CENTER MIAMI FL 300 AM EDT WED APR 20 2011 MARINE WEATHER DISCUSSION FOR THE GULF OF MEXICO...CARIBBEAN SEA AND TROPICAL N ATLC...AND SOUTHWEST NORTH ATLC S OF 31N W OF 55W. SOUTHWEST N ATLC W OF 55W... UNFORTUNATELY...THE 0100 UTC ASCAT PASS MISSED THE LOW CENTER NEAR 22N58W AND ITS NE QUADRANT WHERE THE STRONGEST WINDS LIKELY LIE. AT 0600 UTC...SHIP V2NA1 REPORTED 30 KT WINDS W OF THE TROUGH THAT EXTENDS N-NW OF THE LOW. BOTH THE 00Z ECMWF AND GFS ONLY SHOW WINDS TO 25 KT HERE AND BOTH MODELS SHOW AN INCREASE IN THE MAXIMUM WIND ASSOCIATED WITH THE SYSTEM OVER THE NEXT 6-12 HOURS. THIS TIME LAST NIGHT...BOTH OF THESE MODELS WERE ALSO UNDERDONE COMPARED TO THE STRONGEST WINDS REPORTED BY ASCAT. THERE SEEMS TO BE A TREND WITH THIS SYSTEM FOR THE MODELS TO BE TOO LIGHT WITH THE STRONGEST WINDS. THEREFORE...WILL KEEP THE GALE WARNING UP FOR THIS LOW DESPITE THE LACK OF SUPPORT FROM THE 00Z GEFS AND THE LACK OF A GALE WIND BARB FROM THE 00Z ECMWF. THE LAST TWO RUNS OF THE ECMWF HAVE BEEN ON THE NORTHERN EDGE OF THE GUIDANCE. THE 12Z/19 ECMWF ENSEMBLE MEAN NEVER TAKES THE LOW N OF 27N WHILE THE 00Z ECMWF IS FARTHER N THAN THIS MEAN. BELIEVE THE ECMWF FORECAST ALLOWS THE LOW TO BE PULLED TOO FAR N BY THE DEEP LAYER TROUGH PASSING TO ITS N ON THU. MEANWHILE...THE GFS IS A SLOW EASTERN OUTLIER COMPARED TO ALL OF THE OTHER MODELS AND DISSIPATES THE SURFACE LOW MORE QUICKLY AS IT ALLOWS THAT DEEP LAYERED TROUGH TO PULL EASTWARD ON THE SYSTEM MORE THAN THE OTHER MODELS. NEITHER THE GFS OR ECMWF ALONE LOOKS LIKE A GOOD OPTION. THE UKMET IS A MORE SOUTHWESTERLY OPTION WITH THE LOW TRACK THAN THE GFS AND ECMWF. THE PREFERRED SOLUTION WAS TO BLEND THE GFS AND UKMET THROUGH FRI MORNING WHEN THE ECMWF IS A NORTHERN OUTLIER AND TO BLEND THE UKMET AND ECMWF AFTERWARD WHEN THE GFS BECOMES A WEAK WESTERN OUTLIER. THIS SHOULD ALLOW THE GALE FLAG TO COME DOWN THU AFTERNOON AS THE DEEP LAYER TROUGH APPROACHES...BREAKING DOWN THE RIDGE TO THE N OF THE LOW AND SLACKENING THE PRES GRADIENT. THE GALE CONDITIONS ARE EXPECTED TO REMAIN E OF THE SW N ATLC OFFSHORE ZONE. CARIBBEAN SEA AND TROPICAL ATLC W OF 55W... THE 0238 UTC ASCAT PASS AND SEVERAL SHIP OBSERVATIONS SHOW STRONG E WINDS IN THE GULF OF HONDURAS AND FAR NW CARIBBEAN. THESE WINDS ARE EXPECTED TO DIMINISH BY FRI AS THE RIDGING TO THE N BEGINS TO BREAK DOWN DUE TO THE WESTWARD MOVING LOW PRES SYSTEM OVER THE SW N ATLC. THE ECMWF IS FAVORED WITH THAT LOW AND WITH THE WINDS HERE. FARTHER E...THE BREAKDOWN OF THE SUBTROPICAL RIDGE WILL ALSO BE RESPONSIBLE FOR BRINGING WINDS BELOW 20 KT ALONG THE COAST OF COLOMBIA LATER THIS MORNING. ELSEWHERE...RELATIVELY LIGHT WINDS WILL PERSIST OVER THE MUCH OF CARIBBEAN AND TROPICAL N ATLC THROUGH SAT WITH THE SUBTROPICAL HIGH AND TRADE WINDS DISTURBED BY THE PERSISTENT DEEP LAYER TROUGHING OVER THE WESTERN PORTION OF THE SW N ATLC AREA. THE FINAL EXCEPTION WILL IN THE WINDWARD PASSAGE WHERE FRESH TO OCCASIONALLY STRONG NE WINDS WILL CONTINUE THROUGH SUN. GULF OF MEXICO... THERE ARE NUMEROUS OBSERVATIONS OF FRESH SE WINDS IN THE WESTERN GULF AND THE 0240 UTC ASCAT PASS SHOWS STRONG WINDS JUST N OF THE YUCATAN. THE AREA OF FRESH TRADE WINDS WILL SHRINK PRIMARILY TO THE WESTERN GULF LATER TODAY AND THU AS A COLD FRONT MOVES THROUGH THE LOWER MISSISSIPPI VALLEY AND HIGH PRES PINCHES OFF AHEAD OF THE FRONT OVER THE NE GULF...DISTURBING THE E TO W PRES GRADIENT. BY FRI...THE FRONT WILL LIFT AWAY FROM THE AREA AND THE PRES GRADIENT WILL BE REINVIGORATED BY N TO S TROUGHING BUILDING OVER THE PLAINS. THE ECMWF IS FAVORED BY THE WEEKEND AS THE PARTIAL BREAKDOWN OF THE SUBTROPICAL RIDGE BY THE APPROACHING LOW PRES SYSTEM IN THE SW N ATLC COMES INTO PLAY. WARNINGS.. ATLC... .GALE WARNING FROM 23N TO 27N BETWEEN 55W AND 65W. CARIBBEAN... .NONE. GULF OF MEXICO... .NONE. FOR ADDITIONAL INFORMATION PLEASE VISIT HTTP://WWW.HURRICANES.GOV/MARINE $$ FORECASTER SCHAUER