Marine Interpretation Message
Issued by NWS

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AGNT40 KWNM 150123
MIMATN

MARINE WEATHER DISCUSSION FOR N ATLANTIC OCEAN
NWS OCEAN PREDICTION CENTER WASHINGTON DC
930 PM EDT SUN 14 SEP 2014

.FORECAST DISCUSSION: MAJOR FEATURES/WINDS/SEAS/SIGNIFICANT
.WEATHER FOR THE NORTH ATLANTIC OCEAN W OF 50W FROM 30N TO 50N.

DIAMOND SHOALS BUOY 41025 CONTINUES REPORTING WINDS UP TO 20 KT
THIS EVENING W OF STNRY FRONT. LAST HI RES ASCAT OVERPASS WAS
FROM 1540Z AND INDICATED N TO NE 20 KT EXTENDING TO JUST S OF
CAPE FEAR. LATEST MDLS ARE SLIGHTLY UNDERDONE INITIALLY HERE BUT
ELSEWHERE ARE REASONABLE OVER W ATLC. OPC MDL PREFERENCE
CONTINUES WITH 12Z ECMWF TUE THRU FRI AS IT OFFERS COMPROMISE
WITH STRENGTH OF FRONTAL WAVES TO DVLP OFFSHORE. AS STRONG HIGH
PRES BUILDS TO NEW ENGL COAST FRI AND FRI NGT ECMWF AND GFS ARE
IN REASONABLE AGREEMENT WITH STRENGTHENING OFFSHORE PRES
GRADIENT. OVERALL WILL NOT BE SIGNIFICANT CHANGES FROM PREVIOUS
NT1/NT2 FORECASTS. BOTH 18Z MWW3 AND 12Z ECMWF WAVE MDL SIG WV
HGTS HAVE BEEN IN GOOD AGREEMENT WITH LATEST W ATLC SIG WV HGT
OBS THRU THE EVENING. HOWERVER MWW3 APPEARS TO HAVE MUCH BETTER
HANDLE WITH SWELL ASSOCICATED WITH HURCN EDOUARD OVER NEXT FEW
DAYS.

----------------------------------------------------------------
...PREVIOUS DISCUSSION...

OVER THE SHORT TERM...THE NEW 12Z MDLS REMAIN REL CONSISTENT AND
PRESENT NO SIG FCST PROBLEMS. THE MDLS ALL FCST A HIGH PRES
RIDGE TO BUILD IN FM THE NW TONITE...THEN DRIFT SLOWLY OFSHR
MON/MON NITE CAUSING GNRLY WEAK GRADIENTS (MAINLY 10-15 KT...OR
LESS) THRUT THE CSTL/OFSHR WTRS. THEN ON TUE/TUE NITE THE 12Z
MDLS SHARE SMLR FCST TIMING FOR A WEAK COLD FRONT TO PUSH OFSHR
ACRS THE NT1 AND NRN/CNTRL NT2 WTRS. WHERE THE MDLS DO DISAGREE
IS WHETHER OR NOT A FRONTAL WAVE WL DVLP AS THE FRONT MOVES
OFSHR. THE 12Z UKMET DOES NOT FCST A CLEAR CUT FRONTAL WAVE AT
ALL. THE 12Z NAM/GFS/GEM/ECMWF ALL DO FCST A WAVE TO DVLP BUT
WITH SLIGHTLY DIFFERENT TIMING/STRENGTH. THE 12Z
NAM/GFS/GEM/ECMWF THO DO FCST SMLR ASCD GRADIENTS (WITH MAX ASCD
WINDS GNRLY IN THE 15-20 KT RANGE) WITH THIS FROPA. THEREFORE
PLAN ON POPULATING OUR SHORT TERM WIND GRIDS WITH THE 12Z GFS
10M BL WINDS FOR TONITE THRU MON NITE...THEN MAINLY DUE TO ITS
BETTER FCST CONSISTENCY WITH ITS FRONTAL WAVE WL TRANSITION TO
THE 12Z ECMWF BL WINDS FOR TUE/TUE NITE WITH SM FURTHER EDITS
THEN MADE MAINLY IN DEFERENCE TO THE 12Z ECMWF. SO THE END
RESULT WL BE THAT ONLY MINOR SHORT TERM CHNGS WL BE MADE TO THE
PREV OFSHR FCST PACKAGE.

IN THE LONG RANGE...ON WED INTO FRI THE 12Z MDLS AGREE THAT THE
COLD FRONT WL DRIFT SLOWLY SE ACRS THE SRN NT2 WTRS...BUT THE
MDLS CONT TO DIFFER IN REGARDS TO THEIR FCST TIMING/STRENGTH OF
ANY ASCD FRONTAL WAVES. AS A COMPROMISE BTWN THE STRONGER 12Z
GEM/UKMET AND WEAKER 12Z GFS SOLUTIONS WITH A LOW FCST
CONFIDENCE WULD FAVOR THE 12Z ECMWF SOLUTION AS A COMPROMISE.
WHERE THE MDLS DO THO GNRLY AGREE IS THAT AS STRONG HIGH PRES IS
FCST TO BUILD IN FM THE N THAT A MOD STRONG (PRIMARILY UP TO 25
OR 30 KT AT MOST) ENELY GRADIENT WL DVLP ACRS THE NT2 AND SE
MOST NT1 WTRS. THEREFORE FOR THIS GRADIENT PLAN ON CONTG TO
POPULATE OUR LONG RANGE WIND GRIDS THRU FRI NITE WITH THE 12Z
ECMWF BL WINDS.

.SEAS...THE DIFFERENCES BTWN THE 12Z WAVEWATCH III AND 12Z ECMWF
WAM MDLS ARE MINIMAL THRU MON NITE SO AS WAS DONE PREVLY WL USE
A 50/50 BLEND OF THE TWO MDLS THRU THEN. THEN ON TUE THRU FRI
NITE WL TRANSITION TO A 75/25 BLEND OF THE 12Z ECMWF WAM VS THE
12Z WAVEWATCH III SINCE THE 12Z ECMWF SOLUTION WL BE FAVORED
(BUT ALSO WANT SOME WAVEWATCH III IN THE MIX DUE ITS LONG PERIOD
ESE SWELL FM HURCN EDUARDO THAT IT BRINGS INTO THE OFSHR WTRS
MON NITE INTO TUE).

.EXTRATROPICAL STORM SURGE GUIDANCE...BY LATE THU INTO FRI THE
12Z ESTOFS CONTS TO FCST A SLIGHTLY MR SIG POSITIVE SURGE TO
DVLP ALG THE SE COAST THAN THE 12Z ETSS WHICH LOOKS RSNBL.

.WARNINGS...PRELIMINARY.

.NT1 NEW ENGLAND WATERS...
     NONE.

.NT2 MID ATLC WATERS...
     NONE.

$$

.FORECASTER CLARK/VUKITS. OCEAN PREDICTION CENTER.



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