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000
AGXX40 KNHC 211804
MIMATS

MARINE WEATHER DISCUSSION
NWS NATIONAL HURRICANE CENTER MIAMI FL
204 PM EDT SUN SEP 21 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 THU NIGHT. MWW3/NWPS USED FOR WAVE PARAMETERS. MEDIUM CONFIDENCE.

AN UPPER TROUGH WILL REMAIN PARKED OVER THE EASTERN GULF INTO WED...WITH THE REAR RIGHT QUADRANT JET DYNAMICS ENHANCING CONVECTION PRIMARILY IN THE SOUTHEASTERN GULF. A NEW COLD FRONT WILL MOVE INTO THE NE GULF EARLY TUE AND BECOME DIFFUSE WED. THE PRES GRADIENT WILL REMAIN STRONG OVER THE NE AND N CENTRAL GULF 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...AND A TROPICAL WAVE PASSING THROUGH THE YUCATAN CHANNEL AND THE SW GULF OF MEXICO. THE 00Z ECMWF IS CONSIDERABLY WEAKER OVER THE GULF OF MEXICO WITH THE ENERGY ASSOCIATED WITH THE TROPICAL WAVE COMPARED TO THE GFS. THE REAR RIGHT QUADRANT OF THE JET SHOULD PROVIDE A FAVORABLE ENVIRONMENT FOR THE DEVELOPMENT OF THUNDERSTORMS NEAR THE NORTHERN EXTENT OF THE WAVE AND A MECHANISM TO STEAL AWAY SOME OF THE ENERGY FROM THE WAVE. THE FORECAST WAS ADJUSTED MORE TOWARD THE 12Z GFS BECAUSE OF THIS...BUT THE LACK OF SUPPORT AMONG THE OTHER MODELS LENDED TOWARD BLENDING IN 25 PERCENT ECMWF TO DAMPEN THE WINDS IN THE NORTHERN GULF FOR NOW. THE OFFICIAL FORECAST NOW CALLS FOR WINDS AT OR ABOVE ADVISORY CRITERIA PRIMARILY IN THE NE GULF WHERE THE PRES GRADIENT IS EXPECTED TO BE STRONGEST WED.




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

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

RELATIVELY BENIGN CONDITIONS WILL CONTINUE 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 THU 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 SW OF THE AZORES EXPECTED TO WEAKEN AS IT MOVES S AND THEN SW...PASSING UNDER THE RIDGE AXIS. THIS WILL KEEP THE PRES GRADIENT WEAK ACROSS THE CARIBBEAN AND TROPICAL N ATLC. THERE ARE SOME DIFFERENCE IN THE MODELS WITH THE STRENGTH OF THIS SYSTEM AS IT PASSES S OF THE RIDGE AND EVEN LARGER DIFFERENCE ARISE AS TROUGHING BUILDS OVER THE SW N ATLC LATE IN THE PERIOD. A BLEND OF THE GFS AND ECMWF WAS USED TO HELP DIMINISH THE UNCERTAINTY IN THE STRENGTH OF THE PRESSURE GRADIENT OVER THE CARIBBEAN.




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

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

A 1404 UTC ASCAT-A PASS CLIPPED THE SE EDGE OF THE WIND FIELD OF THE LOW PRES SYSTEM OFF THE MID ATLC COAST...SHOWING WINDS TO 30 KT WITHIN THE FORECAST AREA S OF 31N. THE GFS HAS BEEN THE STRONGEST MODEL WITH THE WIND FIELD OVER THE FORECAST AREA AND WAS FAVORED EARLY IN THE PERIOD WHEN ADJUSTING THE GRIDS...AS WAS THE MWW3. THERE IS GOOD AGREEMENT IN THE 12Z GFS...00Z ECMWF AND THE 12Z GEFS ON WINDS DROPPING BELOW ADVISORY CRITERIA HERE BY 00Z.

A NEW COLD FRONT WILL MOVE OFF THE SE GEORGIA COAST TUE AND SLOWLY PASS INTO NW WATERS THROUGH WED NIGHT. THE 12Z GEFS HAS BACKED OFF ON THE CHANCES OF WINDS EXCEEDING ADVISORY CRITERIA OVER NW WATERS FROM TUE EVENING THROUGH WED. THE 12Z GFS HAS ALSO BACKED OFF CONSIDERABLY ON THE WIND HERE...KEEPING 25 KT WINDS SQUARELY N OF THE FORECAST AREA. THE ECMWF CONTINUES TO BE EVEN WEAKER. IT BUILDS AN INVERTED TROUGH OVER THE SE COAST...AS DOES THE UKMET. THE ECMWF ENS MEAN AND 12Z GEFS SHOW MORE INVERTED TROUGHING HERE THAN THE 12Z GFS. BECAUSE OF THIS...ADJUSTED TOWARD A WEAKER WIND FIELD BY BLENDING IN THE LATEST GFS AND THE 00Z ECMWF...ESPECIALLY FROM TUE NIGHT ON.

$$


.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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