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000
AGNT40 KWNM 281236
MIMATN

Marine Weather Discussion for N Atlantic Ocean
NWS Ocean Prediction Center Washington DC
836 AM EDT Sun May 28 2017

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

For the morning update we will not make any major adjustments to
the ongoing OPC forecast, as the 06Z guidance remains basically
unchanges from the 00Z cycle. We will adjust grids to fit current
conditions and nearby coastal WFO and TAFB forecasts, however.

The latest radar, satellite and lightning density imagery
indicates scattered heavy thunderstorms occurring well off the
Delmarva coast, or roughly 150-250 NM east of the North
Carolina-Virginia border over outer offshore zone ANZ925,
drifting off east and southeast. The latest SREF thunderstorm
guidance indicates that this activity will persist over this
general area for most of today, as a nearly stationary front and
weak low prevail over and west of the central NT2 waters. The
thunderstorm activity will then likely tend to lift more
northeastward tonight into Monday as the front becomes a warm
front and lifts northward. Locally strong winds exceeding gale
force and very rough seas can be found in or near any of these
heavier thunderstorms.

Except for the higher seas in and near thunderstorms, we will
not make major changes to the previous forecast for the morning
update.

-----------------------------------------------------------------
PREVIOUS DISCUSSION...

Will base the early morning grids on the latest 00Z GFS guidance
throughout the next several days in what looks to be a rather
quiet weather period with weak gradients, resultant light
surface winds, and relatively flat seas.

Convection beginning to fire along a forming boundary over the
mid-Atlantic waters, basically extending east from Cape Henry
along 37N. Convergence along the front seen in the most recent
MetOp-B ASCAT overpass just after 01z; weak north to northeast
5-10 kt winds were remotely sensed poleward of the boundary,
while south to southwest 5-15 kt retrievals were returned south
of the front. Based on regional SREF probablisitic and 4km NAM
guidance, scattered showers and thunderstorms are likely as the
boundary creeps north as a warm front later today and into
Monday through the northern NT2 and NT1 offshore zones.

Overall there were no surprises in the 00Z model suite. Weak low
likely to form this morning along the aforementioned front around
the Norfolk area, then lift slowly northeast along the coast
reaching Sandy Hook by Monday afternoon, before turning east
along 40N Monday night and pulling east of OPC waters by Tue eve.
Persistent onshore e to se flow expected north of the low and
warm front, and with good support from the UKMET/NAM and to a
lesser extent the ECMWF, will continue to squeeze out a few 25 kt
winds. Series of low pressure troughs are expected to move
across the waters Tue and Wed, followed by a weak cold front Wed
night into Thu. High pressure progged to build over the offshores
behind the front Thu night.

Seas: since staying close to the GFS throughout, see no reason to
stray far from WW3 guidance. Only modifications: in persistent
east to southeast flow where wave models tend to underperform,
will be adding edit areas that increase significant wave heights
10-15 percent. Realistically, this will only be increasing seas
from 5-6 ft to closer to 6-7 ft for the waters adjacent to the
Delmarva, New Jersey, and Long Island coasts.

Extatropical Storm Surge Guidance: ETSS positive surge values
approaching .3 to .5 ft output in latest guidance Monday from
Cape May to near Montauk Point. ESTOFS output is running a little
higher, closer to the .5 to 1 ft range.



.WARNINGS...Preliminary.

.NT1 New England Waters...
     None.

.NT2 Mid-Atlantic Waters...
     None.

$$

.Forecaster Mills/Collins. Ocean Prediction Center.


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