

338 

AGNT40 KWNM 170117

MIMATN



MARINE WEATHER DISCUSSION FOR N ATLANTIC OCEAN

NWS OCEAN PREDICTION CENTER WASHINGTON DC

917 PM EDT TUE AUG 16 2016



.FORECAST DISCUSSION: MAJOR FEATURES/WINDS/SEAS/SIGNIFICANT

.WEATHER FOR THE NORTH ATLANTIC OCEAN W OF 50W FROM 30N TO 50N.



CRNT SFC RPRTS...AND 18Z RSCAT AND 15Z ASCAT WIND RETRIEVALS INDC

SRLY FLOW UP TO 20 KT OVR THE SHELF WATERS IN NT1...AS A COLD

FRONT MOVING INTO NEW ENGLAND APRCHS THE COAST. 18Z GFS WINDS ARE

INIT A LTL HIGH WHEN COMPARED WITH THE DATA...AND SEEM A LTL

OVERDONE IN NT1 IN THE SW FLOW OVER THE 24 HOURS. THE PREV FCST

FAVORED THE 12Z GFS 10M WINDS FOR THE FCST...SO ATTM PLANNING ON

TONING IT DOWN SLIGHTLY OVR NT1 IN THE SW FLOW...TO ACCT FOR THE

STABLE PBL WHICH SHUD LIMIT MIXING. ALSO PLANNING ON DCRSG THE

ASSOC SEAS SLIGHTLY...TO ACCT FOR THE LOWER FCST WINDS.



OTRW...THE 12Z/18Z MDLS AGREE IN THE SHORT TERM ON THE TMG OF THE

AFOREMENTIONED FRONT AS IT IS XPCTD TO PASS THRU NT1 WED INTO WED

NGT...AS HIGH PRES PERSISTS OVER THE SRN WATERS. THE MDLS ALSO

AGREE ON THE NEXT SYS ON THU NGT INTO FRI THRU NT1...WHICH IS

XPCTD TO BE VRY WK. THE PREV FCST FAVORED THE GFS SOLN...WHICH IS

SUPPORTED SOMEWHAT BY THE REST OF THE 12Z MODELS...SO NOT XPCTG TO

MAKE ANY SIG CHANGES IN THE SHORT RANGE.



IN THE EXTENDED...THE MDLS ALL INDC AN UPR RDG WL BUILD OVER THE

WRN ATLC...WITH A FEW WK H5 VORTS OVR NT2. THERE IS A BIT OF

DISAGRMT ON THE LOC AND INTNSTY OF THE VORT MAXES...ALTHO MOST

SOLNS INDC THEY WL RMN FAIRLY WK. THE PREV FCST STAYED WTIH THE

12Z GFS THRUT THE RMNDR OF THE FCST PD...AND PLANNING ON STAYING

ALONG THOSE LINES AS A RESULT OF THE UNCERTAINTY RAISED BY THE MDL

DISAGRMT.



-----------------------------------------------------------------

PREVIOUS DISCUSSION...



STRONG UPPER LEVEL HIGH PRES THAT HAS DOMINATED ACROSS THE

FORECAST WATERS WILL START TO WEAKEN IN THE SHORT TERM AND WILL

REMAIN WEAK THROUGH THE EXTENDED PERIOD.



THE LATEST SAT IMG STILL INDC TSTMS OVER THE CENTRAL WATERS WITH

EVEN STRONGER TSTMS JUST E OF THE BALT CANYON. THE CURRENT SYNOP

OBSERVATIONS INCLUDING THE ASCAT PASS AT 1420Z SHOW MAX WINDS TO

20 KT BUT SLIGHTLY HIGHER IN AREAS WITH TSTMS. AT 18Z THE NCEP MAP

NOW HAS A WARM FRONT ACROSS THE CENTRAL WATERS IN THE AREA WITH

OBSERVED TSTMS. BROAD HIGH PRES HAS WEAKENED TO 1025 MB E OF THE

REGION BUT STILL HAS ITS WRN RIDGE EXTENSION ACROSS THE WATERS.

THE PRES GRADIENT IS FAIRLY WEAK AND ALL THE MODELS HAVE GENERALLY

INITIALIZED WELL WITH THE OBSERVATIONS. HOWEVER...THE MODELS HAVE

SOME MINOR DIFFERENCES IN THE ACTUAL POSITION OF THE HIGH PRES

1025 MB OVER THE N-ERN EDGE OF THE WATERS. THE GFS/NOGAPS/UKMETHR

MATCH THE POSITION OF THE HIGH WHILE THE ECMWFHR/NAM/CMC HAVE IT

OVER THE BALTIMORE CANYON. THE OTHER NOTABLE DIFFERENCES ARE WITH

THE TRACK AND STENGTH OF THE LOW PRES THAT WILL PASS NEAR THE NRN

WATERS. THE NAM/ECMWFHR SHOW THE LOW WILL PASS FARTHER N OF THE

WATERS WHILE THE GFS/UKMWETHR/NOGAPS/CMC BRING IT CLOSER TO THE

WATERS WITH UKMETHR BEING A TARDY FASTER. THE MODELS ARE WITHIN 2

MB MSLP DIFFERENCE ON THE SAME LOW AND WITHIN 10 KT WINDS SPEED

DIFFERENCE. ONLY CMC HAS WINDS TO 35 KT OVER THE FORECAST WATERS

AS THE LOW GETS CLOSER TO THE WATERS.



THE ENERGY THAT WILL MAINTAIN THE LOW WILL DROP DOWN FROM THE

UPPER LOW PRES TROF AND WILL PASS JUST N OF THE REGION. THERE WILL

ALSO BE SOME ENERGY TO THE S THAT WILL MOVE WITH THE TROF OVER THE

NRN WATERS. A MODEL CHOICE SHOULD BE ONE THAT WILL BRING THE LOW

PRES CLOSER TO THE WATERS SINCE THERE WIL BE TWO SOURCES OF ENERGY

PASSING THE NRN REGION BUT WINDS SHOULD NOT REACH GALE FORCE

THRESHOLD. WILL GO WITH GFS BECAUSE IT HAS INITIALIZED WELL AND

ALSO GIVES THE SOLUTION OF A BLEND BETWEEN THE EXTREME VALUES IN

BOTH THE PRES AND WIND SPEED. THE SYNOP SYSTEMS WILL MOVE E FAST

ENOUGH AND THAT WILL THWART DEEPENING OF THE LOW PRES AS IT PASSES

NR THE WATERS. AS SUCH...WITH MOD TO HIGH CONFDC WILL KEEP WINDS

BELOW GALE FORCE AS THE LOW PASSES TO THE N. THE GENERAL SYNOP

PICTURE WILL BE STARTING TO WEAKEN THE HIGH PRES OVER THE WATERS

IN THE SHORT TERM AND MAINTAIN A RELAXED PRES GRADIENT THRU THE

FORECAST PERIOD AND SO THE WINDS WILL REMAIN BELOW GALE FORCE. 



.SEAS...THE SEAS ARE EQUALLY LOW RANGING BETWEEN 3 AND 5 FT OVER

THE NRN WATERS AND 2 TO 4 FT OVER THE SRN WATERS. NWW3 FITS VERY

WELL WITH THE SEAS PATTERN AND IS CLOSE TO THE ECMWFWAVE. BOTH

WAVE MODELS HAVE BEEN QUITE CONSISTENT AND SO WILL CONTINUE WITH

NWW3 FOR THE SEAS. SE SWELL WILL PREVAIL INITIALLY ACROSS THE

REGION BUT THE NRN HALF WILL HAVE A SW SWELL AS THE LOW PRES

PASSES TO THE N. THE SEAS WILL REMAIN BELOW 6 FT IN THE SE SWELL

BUT WILL BRIEFLY BUILD TO 9 FT OVER THE NRN WATERS THEN SUBSIDE TO

BELOW 8 FT.



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



.WARNINGS...PRELIMINARY.



.NT1 NEW ENGLAND WATERS...

     NONE.



.NT2 MID ATLC WATERS...

     NONE.



$$



.FORECASTER KELLS/MUSONDA. OCEAN PREDICTION CENTER.

