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AGNT40 KWNM 240738
MIMATN

Marine Weather Discussion for N Atlantic Ocean
NWS Ocean Prediction Center Washington DC
338 AM EDT Sun Jun 24 2018

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

Over the short term, today through Mon, the 00Z models remain in
good agreement. We will populate grids today through Mon with a
75 percent previous grids, 25 percent 00Z Warw blend, which will
mainly just freshen-up the ongoing OPC forecast over the next
couple of days. The main concern will continue to be the locally
strong winds near or exceeding gale force and very rough seas in
and near the heavier thunderstorms that impact the waters over
the next day or two. The latest GOES-IR imagery, radar and
lightning data show scattered heavy thunderstorms moving E and
NE from S of Cape Cod to Georges Bank, with a few thunderstorms
also off the Delmarva coast and just N of Cape Hatteras. The
latest SREF thunderstorms guidance indicates that the highest
chance for thunderstorms will be near and off the southern New
England and mid-Atlantic coast today into Mon. An ASCAT overpass
from 0147Z last evening indicate the strongest winds over the
offshore waters were near and just S of the north wall of the
gulf stream, with S to SW winds up to 25 kt in this region, with
these winds matching up quite well with the ongoing OPC grids.
We still expect weak low pressure to move E away from the New
England waters today with another low approaching the New
England coast by this evening, moving E and NE over the Gulf of
Maine tonight, and passing S of Nova Scotia Mon. There appears
to be a good chance for gales developing with the low as it
strengthens and passes S of Nova Scotia Mon, with any gales
likely remaining E of the offshore waters. A cold front
associated with this low will push S over the New England waters
tonight, and then the remainder of the area Mon, with high
pressure slowly building SE behind the front from the Great
Lakes. Forecast confidence over the short term is above average,
with no hazards expected over the offshore waters.

Over the medium range, Mon night through Thu night, we will
populate grids with the 00Z GFS and use the stability tool which
places the stronger first sigma layer winds over the unstable
areas and lower 10 meter winds over the stable areas Mon night
into early Thu, as high pressure overspreads the waters from NW
to SE Mon night into Wed, with the high moving E of the area
late Wed into early Thu. The cold front noted above, will stall
over the southern NT2 waters, or off the SE coast, Mon night and
persist into Wed night. Some of the 00Z guidance is suggesting
that low pressure will form along the front off the far SE coast
later Tue into early Thu, with the 00Z GFS showing a weaker low
further W, when compared to the stronger 00Z ECMWF solution. For
now, we will follow the weaker GFS solution, and continue to
monitor the guidance over the next few days. For Thu and Thu
night, we will trend the forecast toward the more conservative
GFS 10 meter wind solution with the low just off the SE coast
remaining weak, and lifting N near the coast as a weakening cold
front approaches from the W and NW. By early Fri, we will trend
the forecast and grids toward the WPC medium range guidance.
Confidence levels fall from above average Mon night and Tue, to
near average by Wed, and to somewhat below average by Thu and
Thu night. Please closely follow the latest OPC forecast over
the next few days.

Seas...The 00Z Wavewatch and 00Z ECMWF WAM appear to have
initialized better over the waters early this morning verses the
earlier guidance. Sea heights range from around 8 feet off the
mid-Atlantic coast to 3 to 5 feet off the New England and far SE
coasts according to the 06Z RA1 OPC sea state analysis. For the
early morning package we will stay close to the previously
adjusted OPC sea height grids for today into Mon, trend the
grids toward a 50/50 blend of the Wavewatch and WAM later Mon
into early Thu, and then something closer to the 00Z Wavewatch
during Thu and Thu night into Fri to better match the wind
forecast described above.

Extratropical Storm Surge Guidance...N/A.

.WARNINGS...Preliminary.

.NT1 New England Waters...
     None.

.NT2 Mid-Atlantic Waters...
     None.

$$

.Forecaster Mills. Ocean Prediction Center.



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