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AGNT40 KWNM 291440

Marine Weather Discussion for N Atlantic Ocean
NWS Ocean Prediction Center Washington DC
1040 AM EDT Thu Jun 29 2017

.FORECAST DISCUSSION...Major features/winds/seas/significant
.weather for the North Atlantic Ocean W of 50W from 30N to 50N.

At 12z a 1026 mb high was located near 37N70W over the northeast
NT2 waters with its ridge extending across the rest of the NT2
waters and into the NT1 waters. Available ship/buoy obs from the
last several hours have indicated roughly 5-15 kt winds across
the region which meshes well with the ongoing forecast in place.
Will not be making changes to the ongoing forecast in this
intermediate update given agreement between the 06z GFS/NAM and
their prior 00z runs through tonight plus accounting for the
slightly diverging solutions seen in the 00z guidance from Friday
into Sun night. A high pressure ridge remains the dominate
feature through Saturday, with a cold front moving into the
waters later in the day Saturday, pushing east of the NT1 and
northern NT2 waters by late Sunday with its southern portion
hanging back across the central and southern NT2 waters through
Monday night.


The 06Z NCEP surface analysis shows a 1024 mb high centered
offshore near 36N 73W while a cold front east of the waters
transitions to a stationary frontal boundary just south of the
NT2 waters. Current surface observations and ASCAT wind
retrievals from 0145 to 0245Z last evening indicate winds up to
15 kt across the W Atlc except up to 20 kt in easterly flow south
of the high mainly in ANZ835. The 00Z GFS/ECMWF/UKMET/NAM winds
are all initialized well when compared with the data, and all
indicate the high will move east across the central and northern
NT2 waters today into tonight leaving a ridge W into the
Carolinas. The 00Z GFS is in good agreement with the rest of the
00Z models on the aforementioned features, so planning on
starting out with it in the next forecasts.

The 00Z models remain in good overall agreement into Fri, and
indicate high pres will pass east of the area Thu night and
maintain a ridge over the NT2 waters through Sat. The models
have also been indicating a weak warm front passing NE across
the NT1 waters later today and Thu night with winds out of the
SW up to 25 kt according to the 00Z ECMWF/UKMET and latest two
runs of the GFS. In contrast, the GEM/NAM both indicate gales in
the warm advection over the cooler waters in the Gulf of Maine,
and seem overdone. The 00Z GFS has trended a little weaker from
the 18Z run, and is now a bit weaker than the 00Z ECMWF. Plan on
shifting to a 50/50 blend of the 00Z GFS and 00Z ECMWF boundary
later winds late Thu night as a compromise and continue using
this blend through Sun night given the small differences in the
southerly flow following passage of the warm front and ahead of
an approaching weak cold front.

The 00Z models all indicate a cold front will approach the area
from the NW Sat and move into the area late Sun or Sun night.
The bulk of the 00Z guidance supports the 00Z GFS with timing of
the front except for 00Z UKMET which is fast outlier. Will
therefore use the 00Z GFS for the remainder of the forecast
through Mon night, with the front forecast to weaken over the
waters with winds 20 kt or less Mon and Mon night.

Seas...The 00Z WNA Wavewatch and 00Z ECMWF WAM both initialized
well over the offshore waters. Only minor differences were noted
between the models, so a 50/50 blend of the models will be used
over the entire forecast period to smooth out the model
differences and with the 50/50 blend used for winds as noted

.Extratropical Storm Surge Guidance...N/A.


.NT1 New England Waters...

.NT2 Mid-Atlantic Waters...


.Forecaster Holley/Bancroft. Ocean Prediction Center. is the U.S. government's official web portal to all federal, state and local government web resources and services.