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AGNT40 KWNM 240122
MIMATN

Marine Weather Discussion for N Atlantic Ocean
NWS Ocean Prediction Center Washington DC
922 PM EDT Wed May 23 2018

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


Cold front has pushed south across the mid-Atlantic waters this
evening, and is now draped from near Cape Hatteras ENE through
the waters between 35N-37N. The boundary remains a focal point
for ongoing convection, with the lightning strike density product
revealing widespread thunderstorms equatorward of the front.
Caution for locally very strong winds exceeding gale force and
very rough seas in and near the stronger thunderstorms.

Overall the ongoing forecast grids look to be in excellent shape
this evening, and aside from only minor edits in deference to
coastal forecast offices and TAFB, will not be make major
changes to the grids already in place. For more details, see
discussion below.

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PREVIOUS DISCUSSION...

Per the 18z Atlantic surface analysis a stationary front was
located across the northeast NT2 waters, extending into the
southern NT1 waters, where it transitioned into a cold front off
the southern New England coast. High pressure ridging was located
over the remainder of the NT2 offshore waters. Latest available
ASCAT high resolution imagery revealed 5-15 kt winds in the NT1
waters with winds increasing to 10-20 kt over the NT2 waters.
GOES16 satellite imagery as well as lightening data continued to
show a line of thunderstorms over the northeast NT2 waters
extending southwest into the southwest NT2 waters. As always,
the possibility for locally very strong winds exceeding gale
force and very rough seas in and near the stronger thunderstorms
remains possible.

12z guidance continued to remain in general agreement through
late Saturday, so similar to the last two forecasts will use the
latest GFS in this package. The aforementioned frontal
boundaries over parts of the offshore waters will slide south
through the mid- Atlantic and southern waters through tonight.
The front will stall and gradually dissipate Thursday into Friday
over the southern NT2 waters. Guidance agrees strong low
pressure will pass through eastern Canada Thursday through Friday
night with a strong cold front approaching the Gulf of Maine
Thursday night into Friday, weakening as it passes through the
far northern waters. The front will is expected to weaken and
dissipates Sat. Concerning Sunday and Monday, days 4 and 5, the
latest GFS continues to be the farthest east in regards to AL90,
bringing the center of the system across Florida Sunday and into
Georgia by Monday. Based on this scenario the 12z GFS increases
winds over the southwest NT2 waters Sunday into Monday with the
model suggesting warning hazards during a time on Sunday. Given
the GFS continues to remain an apparent outlier when compared to
the rest of the global guidance, will favor using the 12z ECMWF
which keeps AL90 over the eastern and central Gulf of Mexico
Sunday and Monday. Winds are still anticipated to increase over
parts of the southern NT2 waters near the end of the period as
what becomes of AL90 interacts with high pressure ridging
anticipated over the waters, but these winds remain below that of
the GFS and certainly below warning hazard levels.

.SEAS...The WW3 and ECMWF WAM initialized fine at 12Z, and with
continued little differences between the guidance into Saturday
evening, will use the 12z WW3 through that time frame. Then
trend toward and use the 12z ECMWF WAM wave guidance from late
Saturday on. Beneath its continued far east track of AL90, the
12z WW3 continues to build seas to 15 feet. This latest official
forecast and the ECMWF WAM will contain seas generally 6-9 feet
or less near the end of the period.

.EXTRATROPICAL STORM SURGE GUIDANCE...No significant positive
surge events are expected through the next few days.



.WARNINGS...Preliminary.

.NT1 New England Waters...
     None.

.NT2 Mid-Atlantic Waters...
     None.

$$

.Forecaster Collins/Holley. Ocean Prediction Center.


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