Marine Interpretation Message
Issued by NWS

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825
AGNT40 KWNM 250103
MIMATN

MARINE WEATHER DISCUSSION FOR N ATLANTIC OCEAN
NWS OCEAN PREDICTION CENTER WASHINGTON DC
903 PM EDT SAT SEP 24 2016

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

NOTE: OPC IS PROVIDING FORECAST SUPPORT TO NHC FOR T.S KARL AND
T.D. LISA...SO WL BE BRIEF.

A COLD FRONT CONTS TO SINK SLOWLY S ACRS THE CNTRL NT2 WTRS AT
THE MOMENT WITH MAX ASCD WINDS GNRLY IN THE 15-25 KT IN THE
POSTFRONTAL NLY GRADIENT...HIGHEST ACRS THE NE MOST NT2 WTRS. MAX
ASCD SEAS ARE LKLY IN THE 6-8 FT RANGE...ALSO HIGHEST OVER THE NE
NT2 WTRS...WHICH ARE IN LINE WITH THE 18Z WAVEWATCH III AND 12Z
ECMWF WAM MDLS AT THE MOMENT.

OVER THE SHORT TERM...THE 18Z GFS/NAM REMAIN CONSISTENT VS THEIR
PREV RESPECTIVE RUNS AND IN RSNBLY GOOD AGRMT WITH THE OTHER 12Z
GLOBAL MDLS THAT THE COLD FRONT WL CONT TO DRIFT S ACRS THE CNTRL
NT2 WTRS TONITE...THEN ACRS THE SRN NT2 WTRS SUN/SUN NITE WHILE A
HIGH PRES RIDGE BUILDS TO THE COAST SUPPORTING A MOD STRONG (RMNG
IN THE 15-25 KT RANGE) POSTFRONTAL GRADIENT. THE MDLS THEN REMAIN
IN GOOD AGRMT THAT THE RIDGE WL MOV OFSHR MON...THEN PASS E OF THE
OFSHR WTRS MON NITE WHILE A COLD FRONT APRCHS FROM THE W CAUSING A
STRENGTHENING SLY PREFRONTAL GRADIENT TO DVLP OFF THE MID ATLC AND
SRN NEW ENGLD COASTS. SO WITH THE MDLS RMNG CONSISTENT DO NOT PLAN
ON MAKING ANY SIG SHORT TERM CHNGS THRU MON NITE TO THE PREVLY
POPULATED FCST WINDS.

IN THE LONG RANGE...THE LATEST MDLS GNRLY AGREE THAT THE COLD
FRONT WL PUSH OFSHR TUE/TUE NITE WITH THE 18Z GFS NOW FCSTG A
STRONGER SLY PREFRONTAL GRADIENT WITH SM GALE FORCE ASCD SLY BL
WINDS ACRS THE NT1 WTRS. WITH ALL OF THE OTHER MDLS FCSTG A WEAKER
PREFRONTAL GRADIENT WL CONT TO HOLD OFF ON FCSTG ANY PSBL GALES
THEN. THE DISPARITY THEN INCREASES SIGLY BTWN THE LATEST GLOBAL
MDLS WED AND BEYOND. THE 12Z GEM/NAVGEM FCST THE MOST PROGRESSIVE
PATTERN FOR WED THRU THU NITE WHILE THE 12Z/18Z GFS AND 12Z
UKMET/ECMWF BY FCSTG A MORE AMPLIFIED UPR LVL PATTERN WITH A
CLOSED UPR LOW FCST TO APRCH THE MID ATLC COAST THU/THU NITE ARE
LESS PROGRESSIVE. SO WITH THE 18Z GFS TRENDING SLOWER THAN ITS
PREV 12Z RUN...WL FAVOR THE LESS PROGRESSIVE 12Z ECMWF SOLUTION
FOR WED THRU THU NITE AND AS A RESULT WL BLEND IN ITS FCST BL
WINDS AND ASCD ECMWF WAM FCST SEAS TO THE PREVLY USED FCST GRIDS
THEN.



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

THE SAT IMG STILL INDC AREA OF HIGH PRES OVER THE NRN WATERS AND
A BAND OF LIGHTNG ACROSS SRN WATERS WITH MORE INTENSE LIGHTNG TO
THE E OF THE SRN WATERS ASSOCIATED WITH T.S KARL. THE LATEST 18Z
OBSERVATIONS SHOW N TO NE WINDS 10 TO 15 KT OVER THE NRN WATERS
AND W TO NW WINDS 5 TO 10 KT OVER THE SRN WATERS. THE 18Z NCEP MAP
NOW HAS A WEAK COLD FRONT ACROSS THE CENTRAL WATERS WITH A QUASI-
STIONARTY FRONT OVER THE FAR SRN WATERS. INLAND HIGH PRES OVER
CANADA JUST N OF THE GREAT LAKES HAS ITS SE RIDGE INTO THE NRN
WATERS. THE PRES GRADIENT IS VERY SLACK ACROSS THE WATERS.

IN THE UPPER LEVELS MODELS SUGGEST LITTLE ENERGY OVER THE SRN
WATERS BUT MORE SIG ENERGY IS JUST N OF THE REGION. IN THE SHORT
TERM SOME OF THE ENERGY FROM THE N WILL SPREAD S INTO THE FAR NRN
WATERS BUT AN UPPERLEVEL RIDGE WILL QUICKLY PUSH THE ENERGY E OF
THE WATERS AND MAINATIN JUST A RIDGE ACROSS THE REGION. THE
RESULTANT SFC FEATURES WILL BE A COLD FRONT MOVING SE ACROSS THE
NRN AND CENTRAL WATERS THEN A RIDGE WILL SET IN AND KEEP A RELAXED
PRES GRADIENT.

THE GLOBAL MODELS HAVE INITIALIZED WELL ESPECIALLY THE PRES FIELD
AND WITH ONLY SMALL DIFFERENCES IN THE WIND SPEED. IN THE SHORT
TERM ALL THE MODELS GFS/ECMWFHR/UKMETHR/NOGAPS/CMC AGREE WELL ON
THE FEW SYNOP FEATURES OVER THE FRCST WATERS BUT DIFFERENCES EXIST
AFTER 36 HOURS WHEN GFS AND ECMWFHR BECOME MORE PROGRESSIVE THAN
THE REST WITH LOW PRES THAT WILL PASS TO THE NW. OTHERWISE THE
MODELS AGREE ON KEEPING WINDS BELOW GALE FORCE THRU THE PERIOD.
WILL STAY WITH GFS FOR MOST OF THE PERIOD THEN ECMWF IN THE
EXTENDED PERIOD. IN THE SHORT TERM T.S KARL WILL REMAIN TO THE E
AND BE MOVING FARTHER AWAY FROM THE WATERS. LOW PRES WILL PASS TO
THE NW OF THE REGION AS IT PULLS A FRONT E OVER THE WATERS IN THE
EXTENDED PERIOD.

.SEAS...THE SEAS ARE STILL EQUALLY SMALL WITH PEAKS TO ONLY 8 FT
OVER THE ERN PARTS OF THE SRN WATERS THAT ARE MAINLY DUE TO LARGE
SWELL FROM T.S KARL. NWW3 WAVE MODEL HAS CONTINUED TO INITIALIZE
VERY WELL WITH THE 18Z SEAS PATTERN AND SO IS THE ECMWFWAVE MODEL.
BOTH ECMWFWAVE AND NWW3 WAVE MODELS HAVE BEEN QUITE CONSISTENT
WITH OBSERVATIONS IN THE PAST AND AGREE WELL THRU MOST OF THE
FORECAST PERIOD. WILL NOT MAKE MAJOR CHANGES TO THE PREVIOUS
FORECAST AND WILL CONTINUE WITH NWW3. IN THE SHORT TERM SEAS WILL
REMAIN HIGHER OVER THE FAR ERN PARTS. THE SEAS WILL SUBSIDE TO
LESS THA 8 FT OVER THE ERN PARTS BUT BUILD OVER THGE NRN WATERS TO
8 FT IN THE EXTENDED PERIOD.


.EXTRATROPICAL STORM SURGE GUIDANCE...N/A.



.WARNINGS...PRELIMINARY.

.NT1 NEW ENGLAND WATERS...
     NONE.

.NT2 MID-ATLANTIC WATERS...
     NONE.

$$

NOTE: ON OCTOBER 06, 2016...THE NWS FTPMAIL SERVICE WILL DISABLE
THE CURRENT EMAIL ADDRESS. THE NEW EMAIL ADDRESS IS LIVE NOW.
PLEASE TRANSITION TO IT AS SOON AS POSSIBLE TO AVOID A SERVICE
DISRUPTION.

NEW EMAIL ADDRESS...NWS.FTPMAIL.OPS@NOAA.GOV
/ALL LOWER CASE LETTERS/

FOR THE SERVICE CHANGE NOTICE...PLEASE GO TO
HTTP://WWW.NWS.NOAA.GOV/OS/NOTIFICATION/SCN16-37FTPMAIL.HTM
/ALL LOWER CASE LETTERS/

.FORECASTER VUKITS/MUSONDA. OCEAN PREDICTION CENTER.



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