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AGNT40 KWNM 280714
MIMATN

Marine Weather Discussion for N Atlantic Ocean
NWS Ocean Prediction Center Washington DC
314 AM EDT Wed Jun 28 2017

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

The latest NCEP surface analysis indicates low pres just E of
the nrn NT2 waters which is pulling a weak cold front across the
srn NT2 zones. In addition, the analysis high pres inland over
the Ohio valley region and a weak low pres trough over New
England. Current surface observations and the Ascat wind
retrievals from 02Z last night indicate winds up to 15 kt across
the W Atlc as the high is starting to build offshore. The 00Z
GFS/ECMWF/UKMET/NAM winds are all initialized well when compared
with the data, and all indicate the front over the srn NT2 waters
will pass SE of the offshore waters early this morning as the
high moves off the Mid Atlc coast by this afternoon. In addition,
the models all indicate the trough over New England will pass E
through the NT1 waters today into tonight. 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 and maintain a
ridge over the NT2 waters through Sun. The models have also been
indicating a weak warm front will move NE across the NT1 waters
Thu and Thu night with winds out of the SW up to 25 kt according
to the GFS/ECMWF/UKMET solutions. In contrast, the 00Z 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 the weakest with the
winds. The 00Z ECMWF seems to be a decent compromise, so planning
on switching to the 00Z ECMWF solution at 12Z Fri.

The 00Z models all indicate another cold front will approach the
area from the NW Sat and move into the area late Sun. The GFS has
been a fast outlier with the timing of the front, as the 00Z
ECMWF/UKMET/GEM are all slower. Since the bulk of the 00Z
guidance supports the ECMWF solution with this feature, will
continue with the 00Z ECMWF through the remainder of the forecast
period.

.Seas...The 00Z Wavewatch and ECMWF WAM are well initialized
with the offshore wave heights as seas currently 4 ft or less in
the offshore waters this morning. The models continued to be
within a ft or so of each other across the offshore waters
through 12Z before small differences start developing as a result
of the aforementioned differences between the associated weather
models. As a result, planning on using a 50/50 blend of the two
models into 12Z Fri. Will then transition to the 00Z ECMWF WAM
exclusively after 12Z Fri to reflect the preferred winds of the
00Z ECMWF.

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

.WARNINGS...Preliminary.

.NT1 New England Waters...
     None.

.NT2 Mid-Atlantic Waters...
     None.

$$

.Forecaster Kells. Ocean Prediction Center.



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