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AGNT40 KWNM 242020

Marine Weather Discussion for N Atlantic Ocean
NWS Ocean Prediction Center Washington DC
420 PM EDT Mon Jul 24 2017

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

In the near term, the primary forecast concern is with regard to
conditions near gale as a surface low moves northeast from off of
the mid-Atlantic coast to the Canadian Maritimes by the end of
the day Tuesday. There were a couple of observations of 40kt
associated with deep convection well off of the coast of Virginia
at 18UTC, and model soundings from both the GFS and ECMWF would
suggest any deep convection would easily mix down to the sea
surface winds of 35 to 40kt. Uncertainty remains with regard to
sustained winds. Observations both from ships and available ASCAT
has capped winds to 30kt outside of deep convection, and the
ECMWF and UKMET 10-meter wind forecasts, along with the GFS
30-meter winds for generosity, are sub-gale over the offshore
waters through tonight. Still have concern that an observation or
two could show a gale-force wind in vicinity of the Gulf Stream,
from about ANZ905 southwest into ANZ925 overnight into Tuesday
morning before the axis of higher 850mb and surface winds moves
northeast. The forecast will reflect winds in much of this area
from 20-30kt, diminishing gradually into Tuesday. Farther north,
the tight gradient that develops as the surface low moves
northeast along the front would also support an increase in wind
to 20-30kt off the coast of Maine, particularly ANZ800. The ECMWF
actually would support marginal gales there, but the GFS and
UKMET are weaker, and will also forecast winds there just below
gale based on the model consensus and the stable air.

Subhazard conditions are highly likely Tuesday night into Friday.
After that, guidance diverges on the strength and placement of
low pressure moving off of the Atlantic coast by Saturday
morning. The GFS and its ensembles continue to be weaker and
farther east with more of an open wave aloft, while the latest
ECMWF is even stronger than its 00UTC run with surface low
pressure deepening to near 992mb by late Friday afternoon off of
the Massachusetts coast. The UKMET is seemingly the most
consistent, with low pressure similar to a track of the ECMWF but
weaker by 5 to 10mb. As with the previous forecast, will continue
to lean toward the UKMET and sub-gale conditions Friday afternoon
into Saturday, while noting that if the ECMWF verifies gale-force
winds would be expected over parts of especially the northern
waters by Friday. Very late in the seven-day forecast period, the
timing and location of individual features varies, and as such
leaned toward the GFS with a front nearly stationary from off the
Georgia and Carolina coasts northeast into the central Atlantic,
with weak surface waves moving along it for an unsettled pattern

.SEAS...Preferred the slightly higher ECMWF WAM in terms of seas
through Thursday, resulting in waves into the lower teens feet in
vicinity of the Gulf Stream in zones ANZ910 and ANZ920 overnight.
With a lean toward the UKMET and GFS for the later parts of the
forecast period, preferred the Wavewatch model adding a foot from
Thursday night through the end of the forecast. Made some
modifications to the Wavewatch based on the expected winds with
the UKMET compromise.



.NT1 New England Waters...

.NT2 Mid-Atlantic Waters...


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