000 AGXX40 KNHC 171858 MIMATS MARINE WEATHER DISCUSSION NWS NATIONAL HURRICANE CENTER MIAMI FL 255 PM EDT TUE APR 17 2012 MARINE WEATHER DISCUSSION FOR THE GULF OF MEXICO...CARIBBEAN SEA AND SOUTHWEST NORTH ATLC S OF 31N W OF 55W. GULF OF MEXICO... A WEAKENING COLD FRONT EXTENDS FROM SW LOUISIANA SW TO INLAND NE MEXICO EARLY THIS AFTERNOON...WHILE THE WESTERN EXTENSION OF AND ATLC RIDGE CONTINUES ALONG 30N IN THE NE GULF. WEAK HIGH PRES IS NOSING SWD BEHIND THE FRONT. AN UPPER LEVEL TROUGH IS MOVING EWD ACROSS ERN TEXAS AND THE FAR NW GULF. ABUNDANT MOISTURE AHEAD OF THE UPPER TROUGH AND ALONG AND E OF THE COLD FRONT IS RESULTING IN SCATTERED SHOWERS AND TSTMS OVER MUCH OF THE WRN AND CENTRAL GULF W OF ABOUT 89W. WINDS AND SEAS HAVE LOWERED OVER MUCH OF THE GULF EXCEPT IN THE ERN PORTION S OF 26N WHERE A TIGHTER PRES GRADIENT BETWEEN THE RIDGE AND LOWER PRES TO ITS SW TOWARDS THE FRONT IS KEEPING SE WINDS OF 20 KT THERE. SEAS TO 8 FT ARE POSSIBLE IN THE FAR SE WATERS...ESPECIALLY THE STRAITS OF FLORIDA. THE FRONT WILL SLOWLY CONTINUE TO MOVE EWD THROUGH WED WHILE TRANSITIONING INTO MORE OF A QUASI-STATIONARY TYPE BOUNDARY. IT SHOULD REACH FROM THE WESTERN FLORIDA PANHANDLE TO THE EASTERN BAY OF CAMPECHE BY WED PER GENERAL MODEL CONSENSUS. WEAK LOW PRES WILL THEN FORM ALONG THE NRN PART OF THE FRONT...AND LIFT NE THROUGH LATE WED NIGHT PULLING THE WEAKENING FRONTAL TROUGH SOME TO THE E BEFORE DISSIPATING OVER NE WATERS THU. ATLC HIGH PRES WILL EXTEND W INTO GULF LATE THU INTO EARLY FRI BEFORE SHIFTING EWD THROUGH SAT ALLOWING FOR LOW PRES TO MOVE FROM TEXAS ALONG THE FAR NRN GULF AREAS. SLY FLOW WILL INCREASE OVER THE ENTIRE GULF BEGINNING LATE FRI AND INTO SAT AS PRESSURES BEGIN TO DECREASE W OF THE AREA. GLOBAL MODELS ARE CONSISTENT WITH TIMING OF COLD FRONT ASSOCIATED WITH THE LOW TO PUSH OFF THE TEXAS AND SW LOUISIANA COASTS FRI NIGHT. THE FRONT IS EXPECTED TO REACH A PSN FROM S CENTRAL LOUISIANA TO WRN BAY OF CAMPECHE EARLY SAT...AND RACE ACROSS THE GULF TO JUST E OF THE GULF BY EARLY SUN EVENING. BOTH THE GFS AND ECMWF DETERMINISTIC MODEL RUNS FROM 12 UTC THIS MORNING AGAIN SHOW STRONG OFFSHORE FLOW BEHIND THIS NEXT COLD FRONT. HOWEVER...THE ENSEMBLE MEMBERS PREFER THE GFS PARALLEL RUN SHOWING LIGHTER WINDS BEHIND THE FRONT AS IT MOVES ACROSS THE GULF. FOR NOW..WILL KEEP SIMILAR WORDING OF NW 25-30 KT WINDS BEHIND THE FRONT LATE FRI NIGHT AND SAT WITH SLIGHT DECREASE ON SUN. AHEAD OF THE FRONT WILL GO MORE WITH A GFS/ECMWF BLEND WITH SLY WINDS INCREASING TO 20 KT FRI AND TO 20-25 KT LATE SAT INTO SUN. WILL BUILD SEAS HIGH BEHIND THE FRONT ALONG THE LINES OF THE GFS PARALLEL WAVEWATCH OF 12 OR 13 FT MAX. THE OTHER MODELS INDICATE MUCH HIGHER SEAS WHICH COULD BE CORRECT IF WINDS ARE AS STRONG AS ADVERTISED BY THE DETERMINISTIC MODELS. WILL HAVE TO WAIT FOR MORE MODEL RUNS TO ACHIEVE HIGHER CONFIDENCE IN THE LONG TERM. CARIBBEAN SEA... A DISSIPATING SHEAR LINE EXTENDS FROM 15N61W TO 14N70W TO 13N78W. OTHERWISE ATLC HIGH PRES WILL MAINTAIN RATHER STRONG TRADES THROUGHOUT...BUT DIMINISH IN AREAL COVERAGE AND STRENGTH THROUGH WED AS THE HIGH WEAKENS. N TO NE SWELLS WILL GRADUALLY SUBSIDE OVER THE EASTERN CARIBBEAN THROUGH WED NIGHT. BY THU...MOSTLY LIGHT WIND AND SEA CONDITIONS ARE EXPECTED THROUGHOUT UNDER A LIGHTER PRES GRADIENT. THE GULF OF MEXICO COLD FRONT IS FORECAST BY THE MODELS TO MOVE ACROSS THE NRN WATERS OF THE NW PORTION OF THE CARIBBEAN SEA ON SUN PRECEDED BY INCREASING S-SW WINDS OF 15-20 KT AND FOLLOWED BY NW-N 15-20 KT WINDS. THIS OF COURSE COULD CHANGE PENDING FUTURE MODEL GUIDANCE. TROPICAL N ATLC S OF 19N W OF 55W... A DISSIPATING SHEAR LINE EXTENDS FROM 16N55W TO 15N61W. WINDS AND SEAS ARE ON THE DOWNWARD TREND NEAR THE SHEAR LINE. ELSEWHERE N SWELLS TO 7 FT CONTINUE TO SLOWLY SUBSIDE. WINDS DIMINISH TO LESS THAN 20 KT AND SEAS TO LESS THAN 8 FT THROUGH SUN. SW NORTH ATLC S OF 31N W OF 55W... A 1025 MB HIGH IS CENTERED AT 30N74W WITH A RIDGE SE TO NEAR 25N65W. NE WINDS CONTINUE TO DIMINISH OVER THE S PORTION OF THE AREA...WITH LIGHTER WINDS IN THE NE PORTION. THE WILL REMAIN NEARLY STATIONARY THROUGH THU AS A WEAK FRONT MOVES INTO THE FAR NW PORTION. THE FRONT WILL THEN LIFT BACK N AS A WARM FRONT LATE THU INTO LATE FRI AS STRONGER RIDGE BUILDS FROM NEAR BERMUDA TO CENTRAL FLORIDA FRI AND SAT. A FRONTAL TROUGH WILL SWEEP S ACROSS THE FAR NE WATERS THROUGH EARLY TONIGHT. IN THE LONG TERM...SELY WINDS INCREASE TO 20 KT OVER NW PORTION OF AREA AHEAD OF APPROACHING COLD FRONT LATE FRI INTO SAT...THEN INCREASE FURTHER TO 25-30 KT LATER SAT AND SUN PER DETERMINISTIC MODELS AND THE GFS PARALLEL GUIDANCE AS THE COLD FRONT MOVES INTO THE NW PORTION...WITH POSSIBLE GALE FORCE WINDS ALONG OR JUST N OF 31N. NOTE... EFFECTIVE APR 3, 2012 AT 1800 UTC THE OFFSHORE WATERS FORECAST ZONES CHANGED FOR THE CARIBBEAN AND SW N ATLANTIC AND THE GULF OF MEXICO. ISSUANCE TIME FOR THE GULF OF MEXICO OFFSHORE WATERS FORECASTS IS REFERENCED TO THE EASTERN TIME ZONE. FOR DETAILS SEE WWW.NHC.NOAA.GOV/ABOUTTAFBPROD.SHTML#OWF GRIDDED MARINE OUTPUT IS AVAILABLE AT WWW.NHC.NOAA.GOV/TAFB/GRIDDED_MARINE (LOWER CASE). GULF OF MEXICO... .NONE. .CARIBBEAN SEA AND TROPICAL N ATLC... .NONE. .SW N ATLC... .NONE. FOR ADDITIONAL INFORMATION PLEASE VISIT HTTP://WWW.HURRICANES.GOV/MARINE $$ FORECASTER WALLY BARNES