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AGNT40 KWNM 270718

Marine Weather Discussion for N Atlantic Ocean
NWS Ocean Prediction Center Washington DC
318 AM EDT Tue Jun 27 2017

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

02Z Ascat winds from late last night indicated variable winds up
to 15 kt over a majority of the offshore waters, and a very small
area with up to 20 kt over the srn NT2 waters in the vicinity of
a weak frontal boundary. The infrared satellite imagery indicates
cloud tops becoming colder over srn NT2, and the lightning
density product indicates convective activity developing along
the front. GFS stability indices indicate a marginally unstable
environment over central and srn NT2, and the SREF indicates
tstms will continue with this boundary as it moves slowly to the
east. Will maintain mention of showers and tstms in the next
forecast as a result. In addition, the 00Z GFS/ECMWF/UKMET/GEM
all indicate an upper trough currently over the Great Lakes will
move east into the area over the next 24 hours or so and take the
front to the east while developing it. The models agree fairly
well on the timing, and all show stronger winds ahead of the
front after it passes to the east of the area. The GFS indicates
no more than 20 kt over the offshore waters with this feature,
and the rest of the 00Z guidance agrees with the GFS on timing
and intensity. Will start out with the 00Z GFS 10m winds in the
next forecast, but will use the first sigma winds over unstable
areas to account for the slightly deeper mixed boundary layer.

The 00Z models then indicate several weak surface boundaries will
move through NT1 into Wed, before a high pres ridge builds across
the NT2 waters Wed into Thu. The models remain in good overall
agreement on the synoptic pattern through Thu, so will continue
with the 00Z GFS which seems representative of the overall
consensus. The 00Z models then indicate a cold front will
approach from the NW Thu night before low pres passes north of
the offshore waters Fri which pulls the front across the area.
The GFS is a little slower than the 00Z ECMWF with the low
passing to the north, and also with the next frontal system
approaching from the W on Sat. The 00Z UKMET/GEM has trended
towards the faster ECMWF solution, and although the timing
difference is slight, the 00Z GFS is a bit of a slow outlier. As
a result, am preferring the 00Z ECMWF solution from 00Z Sat

.Seas...The 00Z Wavewatch and ECMWF WAM are well initialized
when compared with current observations that indicate up to 4 ft
seas in the W Atlc this morning. The models agree generally well
throughout the forecast period, so will use a 50/50 blend of the
two solutions.

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


.NT1 New England Waters...

.NT2 Mid-Atlantic Waters...


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