Marine Interpretation Message
Issued by NWS

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AGNT40 KWNM 281208
MIMATN

MARINE WEATHER DISCUSSION FOR N ATLANTIC OCEAN
NWS OCEAN PREDICTION CENTER WASHINGTON DC
808 AM EDT TUE JUL 28 2015

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

UPDATE...O6Z NCEP SFC ANALYSIS INDICATES A STNRY FNT EXTNDG ACROSS
THE SRN NT2 WTRS AND A LOW PRES TROF APRCHG THE NEW ENG
COAST...BUT OTHW WEAK HI PRES RDG PREVAILS OVER THE OFSHR WTRS.
LATEST AVAIL ASCAT PASSES FROM LAST NITE SHOW LIGHT WINDS OF 15 KT
OR LESS ACROSS THE OFSHR WTRS. LIGHTNING DENSITY DATA AT 1110Z
SHOWS SCT SHOWERS/TSTMS OVER THE NRN GULF OF MAINE AND ASSOCD WITH
THE STNRY FNT OVER THE SRN NT2 ZONES. TWO WEAK COLD FNTS WILL MOVE
ACROSS THE NT1 AND NRN NT2 WTRS TONITE AND WED...THEN AGAIN LATE
SAT AND SAT NITE.

MODELS...THE 00Z MED RNG MDLS ARE IN GUD OVERALL AGREEMENT ACROSS
THE OFSHR WTRS DURG THE FCST PRD...EXCEPT 00Z UKMET SHOWS WHAT
APRS TO BE A TRPCL OR SUBTRPCL LOW IN THE SW PART OF THE NT2 AREA
FOR THU INTO SAT. THE UKMET MOVES THIS LOW NE ALONG THE CAROLINA
COAST LATER SAT...THEN SIGNIF STRENGTHENS IT AS IT TAKES THE LOW
NE OFF CAPE HATTERAS ON SAT NITE. THE REPRESENTATIVE AND
CONSISTENT GFS 10M SOLN WILL BE USED TO POPULATE THE WIND GRIDS
FOR TODAY INTO EARLY THU...THEN WILL GO WITH A 50/50 BLEND OF THE
GFS 10M/ECMWF FOR LATER THU AND THU NITE SINCE THERE ARE SOME
MINOR DIFFS WITH HOW THE MDLS HANDLE THE TRACK OF THE PSBL TRPCL
OR SUBTRPCL SYSTEM. WILL USE PURE ECMWF FOR FRI THRU SAT NITE
SINCE IT LOOKS LIKE A GUD COMPRIMISE BTWN THE SLOW UKMET AND FAST
GFS SOLNS. THE ECMWF MDL WINDS WILL BE CAPPED AT 30 KT FOR FRI
NITE THRU SAT NITE...SINCE THE CONSENSUS OF THE MDLS DOES NOT
SUPPORT GALES ATTM. AM NOT PLANNING TO MAKE ANY SIGNIF CHANGES TO
THE CURRENT FCST TREND.

SEAS...WNA VERSION OF WAVEWATCH III MDL AND ECMWF WAM BOTH
INITIALIZED WELL OVER THE OFSHR WTRS VERSUS LATEST BUOY OBS AND
ALTIMETER PASSES. WILL GO WITH THE WNA WAVEWATCH III FOR THE SHORT
RANGE...THEN SWITCH TO A 50/50 BLEND OF THE TWO MDLS FOR THE
LONGER RANGE TO MATCH UP WITH ATMOS MDLS AND RESOLVE SOME TIMING
DIFFS IN THE NT2 AREA.

EXTRATROPICAL STORM SURGE GUIDANCE...N/A.

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

THE MAIN FCST ISSUE FOR THE EARLY AM PACKAGE WILL BE THE DEVELOPMENT
AND MOVEMENT OF LOW PRES OFF THE SOUTH CAROLINA COAST THU INTO
THE UPCOMING WEEKEND. EXCEPT FOR THIS LOW PRES AREA...LITTLE
CHANGE WILL BE MADE TO THE ONGOING OPC FCST WITH A STNRY FRONT
PERSISTING OVR SRN NT2 WTRS THRU WED...WITH WEAK HIGH PRES N OF
THE FRONT OVR NRN NT2 OFF WTRS PREVAILING OVR THESE WTRS TODAY
INTO WED BEFORE MOVG SE TOWARD BERMUDA LATE WED INTO THU. OVR NT1
OFF WTRS...A WEAK COLD FRONT IS STILL FCST TO MOVE OFFSHORE
TONITE...STALL OVR THE WTRS WED INTO WED NITE...AND THEN RETURN N
AS A WARM FRONT THU. ANOTHER WEAK FRONT WILL APPROACH NT1 WTRS
FROM THE NW THU NITE INTO FRI...AND MOVE SE INTO THE NT1 WTRS FRI
NITE...FOLLOWED BY YET ANOTHER WEAK COLD FRONT SAT NITE. LOW PRES
IS NOW APPEARING MORE LKLY TO FORM OFF THE SOUTH CAROLINA COAST
THU. THE LOW WILL INTENSIFY SOME AS IT TRACKS NE OVER CENTRAL AND
THEN NE NT2 OFF WTRS THU NITE INTO SAT NITE. THERE IS SOME CHANCE
FOR GALES DVLPG OVR PORTIONS OF THE ERN AND NE NT2 OFF WTRS LATER
IN THE WEEK INTO THE WKND. FOR NOW...WE DO NOT FEEL CONFDC ENUF
TO ADD THEM TO THE OFF WTRS FCST...SO WE WILL KEEP ANY GALES THAT
DVLP E OF THE OFF WTRS FOR THE EARLY AM PACKAGE...AND CONT TO
EVALUATE THIS POSSIBILITY OVR THE NEXT FEW DAYS.

MODELS...THE 00Z MDLS ARE IN DECENT AGREEMENT OVR THE OFF WTRS
TODAY INTO EARLY THU. THE 00Z GFS HAS REMAINED QUITE CONSISTENT
FROM ITS PAST FEW MDL CYCLES SO WE WILL ONCE AGAIN USE THE 10M
GFS WINDS FOR THE EARLY AM PACKAGE FOR TODAY INTO EARLY THU. BY
LATE THU INTO THE WKND...THE 00Z GLBL MDL SOLUTIONS BEGIN TO
DIVERGE. THE 00Z UKMET REMAINS AN OUTLIER IN BRINGING A DVLPG AND
RATHER INTENSE LOOKING TROPICAL OR SUB-TROPICAL SYSTEM OVR THE
NT2 OFF WTRS FRI INTO THE WKND...SO IT WILL CONT TO BE IGNORED
FOR THIS PACKAGE. FOR THE EARLY AM PACKAGE FOR THU AND THU NITE
WE WILL USE A 50-50 BLEND OF THE 00Z GFS AND 00Z ECMWF MDLS AS
THEY BOTH INDICATE LOW PRES FORMING OFF THE SOUTH CAROLINA COAST
AND TRACKING SLOWLY NE. THE 00Z ECMWF IS CLOSER TO THE COAST VS
THE 00Z GFS...AND WE BELIEVE A BLEND OF THESE TWO MDLS SEEMS LIKE
THE BEST OPTION FOR THE FCST AT THIS TIME. FOR FRI INTO SAT
NITE...WE WILL TRANSITION TO USING JUST THE 00Z ECMWF MDL GUID.
WE WILL...HOWEVER...LOWER ITS WINDS BY 10 PERCENT OVR NT2 OFF
WTRS FOR FRI INTO SAT NITE...THEREFORE KEEPING GALES OUT OF THE
OFF WTRS FOR THIS FCST PACKAGE...AS WE WOULD PREFER TO SEE A FEW
MORE MDL CYCLES BEFORE ADDING GALES TO THE OFF FCST.

SEAS...BOTH THE 00Z WNA WAVE WATCH III AND 00Z ECMWF WAM WV MDLS
INITIALIZED WELL OVR THE OFF WTRS PER THE LATEST OBS AND
ALTIMETER PASSES. FOR THE SHORT TERM PORTION OF THE FCST THRU WED
NITE WE WILL REMAIN CLOSE TO THE WNA WW3 MDL OUTPUT. FOR THE LONG
TERM PART OF THE FCST...WE WILL USE A 50-50 BLEND OF THE 00Z WNA
WW3 AND 00Z ECMWF WAM MDLS WHICH WILL FIT A LITTLE BETTER WITH THE
WIND FCST AS NOTED ABV. WE WILL ALSO LOWER SEA HTS FCST BY A FT
OR TWO OVR MAINLY ERN AND NE NT2 OFF WTRS BY FRI INTO THE WKND AS
WE LOWERED WINDS BY 10 PERCENT FROM THE MDL GUID OVR THAT REGION
AS DESCRIBED ABV.

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

.WARNINGS...PRELIMINARY.

.NT1 NEW ENGLAND WATERS...
     NONE.

.NT2 MID ATLC WATERS...
     NONE.

$$

.FORECASTER SCOVIL/MILLS. OCEAN PREDICTION CENTER.



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