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AGNT40 KWNM 271347

Marine Weather Discussion for N Atlantic Ocean
NWS Ocean Prediction Center Washington DC
947 AM EDT Sat May 27 2017

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

There will be no warning headlines and seas will subside to
below 8 ft from Sunday through the forecast period. The latest
satellite images show cyclonic circulation northeast of the
waters with few clouds with cold tops over NT1 zones and
Baltimore Canyon. The maximum winds are 25 kt over the eastern
portion of the central waters. At 1200Z the NCEP map has low
pressure 1000 MB just southeast of Nova Scotia with its southwest
trough extending across the Maine waters and associated cold
front passing east of the forecast region. High pressure with
center south of 31N close to 150W extends a weak ridge into the
far southern waters. The pressure gradient is well relaxed across
the forecast waters.

The seas are relatively larger over the eastern portion of the
central and northern waters with a peak at 10 ft. NWW3 and
ECMWFWAVE wave models fit well the 1200Z seas pattern. Both wave
models have been quite consistent with the previous observations
and have been in a fairly good agreement. In the short term,
both wave models agree on seas subsiding to below 8 ft with small
differences just on the areal coverage. The differences continue
into the extended period and so will continue with just NWW3
through the forecast period for seas.

The models GFS/CMC/ECMWFHR/UKMERHR/NAM have initialized well the
1200Z surface observations with just small differences mostly on
the wind direction. In the short term the systems are very weak
and development and dissipation of small temporary features
differ among the models. Otherwise the synoptic pattern remain
about the same and so will just continue with GFS for winds.


At 06Z NCEP surface analysis has low just SE of Nova Scotia with
a slow weakening trend and a trailing low pressure trough SW into
the srn NT1 waters. High resolution ASCAT-B pass from 0140Z with
limited coverage appears to indicate strongest gradients and
winds, up to 30 kt, have shifted east of the offshore waters with
the low leaving moderately strong gradients (up to 20 or 25 kt)
at least over the outer waters and also along and south of the
Gulf Stream and lighter winds north of Hatteras in the inner
waters. Latest 00Z models are initialized well with this low and
the 00Z GFS looks representative. With a bit of instability along
the Gulf Stream in the westerly flow south of the low noted in
the GFS, will populate grids with the 00Z GFS boundary later
winds modified using a tool that places the higher first sigma
level winds over unstable areas and the 10m winds over stable

The 00Z models are in good agreement through the forecast period
with minor differences in placement of a slow moving warm front
with waves moving off the mid-Atlantic coast Sat night into sun
night while a broad upper ridge inland moves to the coast Sun and
offshore Sun night. A frontal system advances toward the coast
ahead of a large upper level system near the Great Lakes and
southern Canada with models especially the 00Z GFS/UKMET/00Z GEFS
ensemble mean hinting at forming a weak triple point low near the
New Jersey coast early Mon and moving it across the NT1 waters
Mon night into Tue night while pushing a weak cold front offshore
with the front stalling across the central NT2 waters Wed and
Wed night with weak associated gradients. For the new forecast
populated with the 00Z GFS through the forecast period again
using the 10m_30m stability tool. No headlines are indicated in
this evolving weak zonal pattern.

Seas...The seas are highest around 10 ft over the NE NT2 waters
closer to the departing low pressure area and 2 to 6 ft closer to
the coast. The wave models 00Z NWW3 and 00Z ECMWFWAVE have
matched well the observed seas pattern and both wave models have
shown consistency in the previous runs. Populated wave grids with
the 00Z NWW3 throughout.



.NT1 New England Waters...

.NT2 Mid-Atlantic Waters...


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