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AGXX40 KNHC 201817
MIMATS

MARINE WEATHER DISCUSSION
NWS NATIONAL HURRICANE CENTER MIAMI FL
217 PM EDT SAT SEP 20 2014

MARINE WEATHER DISCUSSION FOR THE GULF OF MEXICO...CARIBBEAN SEA AND TROPICAL N ATLANTIC FROM 07N TO 19N BETWEEN 55W AND 64W...AND THE SW N ATLANTIC INCLUDING THE BAHAMAS.


...GULF OF MEXICO...

MODEL PREFERENCE: LATEST GFS BLENDED WITH PREVIOUS/OFFICIAL FORECAST THROUGH TUE WITH ECMWF ADDED TUE NIGHT THROUGH WED NIGHT. MWW3/NWPS USED FOR WAVE PARAMETERS. HIGH CONFIDENCE THROUGH MON NIGHT THEN MEDIUM CONFIDENCE.

THE PRES GRADIENT OVER THE N CENTRAL AND NE GULF IS WEAKENING...WITH 20 KT WINDS ONLY OBSERVED FROM ELEVATED PLATFORMS. THESE WINDS WILL DIMINISH TO A GENTLE BREEZE THIS AFTERNOON AND TONIGHT...AND SEAS THERE WILL SUBSIDE AS THE GRADIENT SLACKENS WITH THE LOW E OF THE GULF LIFTS NE...AND THE RIDGE JUST N OF THE AREA BREAKS DOWN. AN UPPER TROUGH WILL REMAIN PARKED OVER THE EASTERN GULF INTO WED...WITH THE REAR RIGHT QUADRANT JET DYNAMICS ENHANCING CONVECTION IN THE EASTERN GULF. A NEW COLD FRONT WILL MOVE INTO THE NE GULF EARLY TUE AND BECOME DIFFUSE BY WED NIGHT. THE PRES GRADIENT WILL REMAIN STRONG BEHIND THE FRONT WITH HIGH PRES BUILDING OVER THE SOUTHEASTERN U.S. STEMMING FROM A STRENGTHENING ANTICYCLONE PASSING FROM THE EASTERN OHIO VALLEY INTO THE NE U.S. TUE THROUGH WED NIGHT. THE GFS CARRIES A STRONGER IMPULSE WESTWARD THROUGH THE GULF TO THE S OF THE RIDGE ATTM THAN THE 12Z NAVGEM AND 00Z ECMWF. HOWEVER...THE 12Z UKMET IS EVEN STRONGER HERE. THE 06Z GEFS SHOWS UP TO A 60 PERCENT CHANCE ON WED OF WINDS AND SEAS MEETING THE ADVISORY CRITERIA OF 20-25 KT AND 8 FT...RESPECTIVELY. CONFIDENCE IS LOW. THE 06Z GFS RUN HAD NOT BEEN AS STRONG. HESITANT TO JUMP ON THE LATEST CHANGE IN THE GUIDANCE. WENT WITH A BLEND OF THE GFS AND WEAKER ECMWF FOR TUE EVE ONWARD. ELSEWHERE...WEAK TROUGHING WILL LINGER OVER THE SW GULF THROUGH PERIOD WITH VERY LITTLE IMPACT ON WINDS AND SEAS.




...CARIBBEAN SEA AND TROPICAL N ATLANTIC FROM 07N TO 19N BETWEEN 55W AND 64W...

MODEL PREFERENCE: LATEST GFS BLENDED WITH PREVIOUS/OFFICIAL FORECAST. MWW3/NWPS USED FOR WAVE PARAMETERS. HIGH CONFIDENCE.

RELATIVELY BENIGN CONDITIONS WILL PREVAIL OVER THE CARIBBEAN AND TROPICAL N ATLC WATERS THROUGH THE FORECAST PERIOD. WINDS AND SEAS ARE NOT EXPECTED TO MEET THE ADVISORY CRITERIA OF 20-25 KT AND 8 FT...RESPECTIVELY...THROUGH WED NIGHT. THE SUBTROPICAL RIDGE N OF THE AREA IS WEAK AND TROUGHING IS BUILDING OVER AND N OF THE BAHAMAS ATTM...KEEPING THE PRES GRADIENT WEAK ACROSS THE CARIBBEAN. THE STRENGTH OF THE SUBTROPICAL RIDGE IS EXPECTED TO CHANGE LITTLE THROUGH WED NIGHT...WITH A CUT OFF LOW CURRENTLY JUST W OF THE AZORES EXPECTED TO WEAKEN AND TAKE A TURN TO THE S AND THEN SW...PASSING UNDER THE RIDGE AXIS. THIS WILL KEEP THE PRES GRADIENT WEAK ACROSS THE CARIBBEAN AND TROPICAL N ATLC. THE GFS FORECAST LOOKS AS GOOD AS ANY HERE.




...SW N ATLANTIC INCLUDING THE BAHAMAS...

MODEL PREFERENCE: LATEST GFS BLENDED WITH PREVIOUS/OFFICIAL. MWW3/NWPS USED FOR WAVE PARAMETERS. MEDIUM CONFIDENCE.

THE 15Z SURFACE ANALYSIS SHOWS 1012 MB LOW PRES OFF THE NE FLORIDA COAST WITH A COLD FRONT EXTENDING SW THROUGH CAPE CANAVERAL. THE 1424 UTC ASCAT-A PASS SHOWS 20-25 KT WINDS N OF 29N BETWEEN 71W AND 75W...LOOKING DECIDEDLY MORE LIKE THE STRONG 12Z GFS COMPARED TO THE OTHER MODELS. THE GFS ALSO APPEARS TO BE HANDLING THE FRESH TO STRONG NE WINDS ALONG THE GEORGIA/SOUTH CAROLINA COAST BETTER THAN THE WEAKER ECMWF WHICH IS SLOWER TO WRAP UP THE LOW AND SEND IT N OF THE AREA THAN THE 12Z MODEL CONSENSUS. THE LOW WILL MOVE N OF THE AREA TONIGHT...BUT THE TRAILING FRONT WILL LINGER ACROSS THE AREA INTO CENTRAL FLORIDA THROUGH MON MORNING BEFORE DISSIPATING. THE 06Z GEFS GOES FROM A 10-20 PERCENT CHANCE OF WINDS AHEAD OF THE FRONT N OF 30N MEETING THE 20-25 KT ADVISORY CRITERIA THIS EVENING TO A 70-80 PERCENT CHANCE BY 06Z SUN. THE GEFS PROBABILITIES DROP OFF TO ZERO BY SUN EVENING AS THE LOW PULLS FARTHER N AWAY FROM THE AREA. THE ECMWF HOLDS ONTO THE WINDS AND SEAS AT ADVISORY CRITERIA FOR 6 MORE HOURS WHILE THE 12Z GFS IS IN LINE WITH THE GEFS. WITH THE GFS APPEARING TO HAVE A BETTER HANDLE ON THE CURRENT CONDITIONS WITH THE DEVELOPING LOW AND IN BETTER AGREEMENT WITH THE 12Z MODEL CONSENSUS...THE FORECAST WILL SIDE WITH ITS SOLUTION.

A NEW COLD FRONT WILL MOVE OFF THE SE GEORGIA COAST TUE AND SLOWLY PASS INTO NW WATERS THROUGH WED NIGHT. THE 06Z GEFS SHOWS A CHANCE OF WINDS EXCEEDING ADVISORY CRITERIA OVER NW WATERS FROM TUE EVENING THROUGH WED NIGHT...WITH PROBABILITIES REACHING AS HIGH AS 60-70 PERCENT WED EVENING. THE 12Z GFS HAS BACKED OFF...GENERALLY KEEPING THE WINDS OVER ADVISORY CRITERIA N OF THE AREA. THE ECMWF IS EVEN WEAKER WHILE THE UKMET DEVELOPS A COASTAL LOW N OF THE AREA AND HAS STRONGER WINDS. THE MIDDLE-OF-THE-ROAD GFS SOLUTION SEEMS BEST FOR NOW UNTIL THE GEFS PROBABILITIES AND THE TREND IN THE OPERATIONAL RUN COME INTO BETTER AGREEMENT ON THE FORECAST HERE.



$$


.WARNINGS...ANY CHANGES IMPACTING COASTAL NWS OFFICES WILL BE COORDINATED THROUGH AWIPS 12 PLANET CHAT OR BY TELEPHONE:


.GULF OF MEXICO... NONE.


.CARIBBEAN SEA AND TROPICAL N ATLANTIC FROM 07N TO 19N BETWEEN 55W AND 64W... NONE.


.SW N ATLANTIC INCLUDING THE BAHAMAS... NONE.

$$

*FOR DETAILED ZONE DESCRIPTIONS PLEASE VISIT: HTTP://WWW.NHC.NOAA.GOV/ABOUTTAFBPROD.SHTML#OWF

NOTE: GRIDDED MARINE FORECASTS ARE AVAILABLE IN THE NATIONAL DIGITAL FORECAST DATABASE (NDFD) AT: HTTP://WWW.NHC.NOAA.GOV/MARINE/GRIDS.PHP

FOR ADDITIONAL INFORMATION PLEASE VISIT: HTTP://WWW.HURRICANE WARNINGS.GOV/MARINE

$$


.FORECASTER SCHAUER. NATIONAL HURRICANE CENTER.

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