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000
AGNT40 KWNM 251237
MIMATN

Marine Weather Discussion for N Atlantic Ocean
NWS Ocean Prediction Center Washington DC
737 AM EST Sun Feb 25 2018

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

Current Conditions...The 06z ncep surface analysis shows a
stationary front extending E to W across the central nt2 waters,
with high pressure ridges over the offshore waters N and S of the
front. Latest available ascat and ascat hi-res passes from last
night show 15 to 20 kt winds over the northern Gulf of Maine and
across the NE part of the nt2 area, with 5 to 15 kt winds
indicated over the remaining offshore waters.

Models/Forecast...The medium range models are in good overall
agreement across the offshore waters for today through Tue, so
the previous wind grids will be used for this timeframe, which
are based on a 50/50 blend of the 00z ecmwf/gfs 10/30m solutions.
Confidence in the gale warnings in the Gulf of Maine and Georges
Bank for today and tonight is average. With the exception of the
gfs, the medium range models are agreed that a developing low
with an associated cold front will move off the mid Atlantic
coast on Thu or Thu night. The gfs is also stronger than the
other models concerning the strength of this low. The models are
showing differences regarding the trajectory and timing of the
developing low, but the 00z ecmwf has strong support from the
latest wpc medium range forecast guidance. The 00z ecmwf will be
used for the wind grids for Tue night through the rest of the
forecast period, except its winds will be capped at 35 kt on Thu
and Thu night in deference to the 00z ukmet which is weaker.

Seas...The ecmwf wam and wavewatch both initialized within one
or two feet of recent observations over the offshore waters,
although the Wavewatch is slightly lower with the seas in the NT2
area. The models are in good agreement through Tue in the
offshore waters, so will go with a 50/50 blend of the ecmwf wam
and wavewatch to smooth minor differences. Then will go
exclusively with the 00z ecmwf wam for Tue night through the
rest of the forecast period, in order to be consistent with the
preferred 00Z ECMWF wind grids.

Extratropical Storm Surge Guidance...The models indicate E to SE
flow in the 20 to 30 kt range ahead of a warm front over the NT1
waters today into tonight. Estofs indicates a positive surge in
the 1.0 to 1.5 ft range along the New Jersey and New England
coasts, with up to 2.0 ft in Long Island Sound. up to +1.0 ft
along the nrn mid Atlc through New England coasts, with up to
+2.0 in wrn Long Island Sound. With most of the models showing
30 to 35 kt winds developing off the mid Atlantic coast around
late Thu and Thu night, estofs shows a positive surge in the 1.5
to 2.0 ft range along the New Jersey and Long Island coasts. For
both surges, the etss indicates values that are less than half
those of estofs, and looks underdone.

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

The latest NCEP surface analysis indicates a weak stationary
front across the central and nrn NT2 offshore waters, and a high
pres ridge to the N over NT1 and a second ridge to the S across
the srn NT2 offshore waters. Current surface observations
indicate generally 20 kt or less over the offshore waters,
with the highest at elevated C-MAN stations along the coast of
Maine. Ascat wind retrievals from 0100 UTC last night indicated
about the same over the area, and 00Z GFS winds are initialized
within 5 kt of the data. The 00Z models all indicate that the
stationary front will start lifting N across the area as a warm
front today, ahead of a shortwave trough moving into the ern
CONUS. The models all indicate an increase in the winds between
the warm front and the departing ridge while low pres develops
near the srn New England coast later today, with the GFS
consistently indicating gales across the Gulf of Maine for
several days now. Most of the 00Z models are indicating at least
30 kt, though the 00Z ECMWF trended slightly weaker and now
indicates 25 kt. Confidence in the previous gale headlines for
today into tonight remains near average, planning on continuing
previous headlines in the next forecast. Will start out with the
previous wind grids which are supported well by the 00Z guidance,
but will make a small decrease in the areal coverage of gales to
reflect the downward trend in the guidance. Will then blend in
the 00Z GFS first sigma winds from 06Z Mon through 21Z Tue, to
reflect the 00Z trends with the associated cold front moving
through the area. Also preferring the first sigma winds as it
reflects the deeper mixed layer in cold advection.

The 00Z models then remain in good overall agreement through
Tue, before the models start differing on the passing of weak low
pressure to the N of the offshore waters. The GFS/GEM have been
slightly slower with the low, though there is a bit of spread
with the very weak feature. The 00Z ECMWF/UKMET remain slightly
faster, and the faster solutions were preferred slightly more by
the previous forecast. As a result of the model spread, confidence
in any one solution is low right now, so planning on staying
near the 00Z ECMWF starting at 00Z Wed mainly to maintain
continuity. The 00Z models then come back into decent agreement
on Thu, with a much stronger system expected to move into the wrn
Atlc. The 00Z GFS/GEM/UKMET/ECMWF all indicate a strong cold
front will move offshore, and generally agree well on the front
despite some minor timing differences. There is some slight
disagreement on the track of the low as it moves offshore, with
the 00Z ECMWF/UKMET/GEM all trending a little S from their
previous runs. The 00Z GFS remains to the N, and takes the low
just S of Long Island. However, the bulk of the 00Z ensemble
guidance, including the WPC medium range guidance is all showing
a much stronger signal for a more southerly solution closer to
the 00Z ECMWF. As fer as the intensity is concerned, the models
are all indicating at least gale force winds winds will develop
ahead of this system, as a strong low level jet is forecast to
develop just ahead of the front with GFS/ECMWF 925 mb winds
indicating up to at least 65 kt over the nrn waters by Thu
night. The GFS has been indicating storm force over NT1 by Thu
night, but confidence is somewhat low as a result of the forecast
range and the lack of support from the rest of the models.
However, confidence with minimal gale force winds is above
average as a result of the strong consensus, so planning on
having gale headlines in most of the NT2 waters. Will also cap
winds at 35 kt to reflect the uncertainty. Otherwise, will
continue with the 00Z ECMWF through the remainder of the forecast
period.

Seas...Both the 00Z ECMWF WAM and Wavewatch have initialized
within one or two feet of the most recent observations in the
offshore waters, although the Wavewatch is slightly lower with
the seas in the NT2 waters. However, the models are in good
agreement through Tue in the offshore waters, so will go with a
50/50 blend of the two models to smooth out the minor
differences. Will go exclusively with the 00Z ECMWF WAM for Tue
night through the rest of the forecast period, mainly to match
up with the preferred 00Z ECMWF winds.

Extratropical Storm Surge Guidance...The models indicate E to SE
flow in the 20 to 30 kt range ahead of a warm front over the NT1
waters today into tonight. The 00Z ESTOFS indicates a surge up
to +1.0 ft along the nrn mid Atlc through New England coasts,
with up to +2.0 in wrn Long Island Sound. In contrast, the 00Z
ETSS shows less than half of what the ESTOFS indicates in most
areas, and seems underdone.

.WARNINGS...Preliminary.

.NT1 New England Waters...
.ANZ800...Gulf of Maine...
     Gale today into tonight.
.ANZ805...Georges Bank west of 68W...
     Gale today.
.ANZ900...Georges Bank east of 68W...
     Gale today into tonight.

.NT2 Mid-Atlantic Waters...
.ANZ915...Hudson Canyon to the Great South Channel...
     Gale Possible Thursday night.
.ANZ920...Baltimore Canyon to the Great South Channel...
     Gale Possible Thursday night.
.ANZ828...Inner Waters from Cape Charles Light to Currituck Beach Light...
     Gale Possible Thursday night.
.ANZ925...Outer Waters from Baltimore Canyon to Hatteras Canyon...
     Gale Possible Thursday night.
.ANZ830...Inner Waters from Currituck Beach Light to Cape Hatteras...
     Gale Possible Thursday night.
.ANZ833...Inner Waters from Cape Hatteras to Cape Fear...
     Gale Possible Thursday night.
.ANZ930...Outer Waters from Hatteras Canyon to Cape Fear...
     Gale Possible Thursday night.
.ANZ835...Inner Waters from Cape Fear to 31N...
     Gale Possible Thursday night.
.ANZ935...Outer Waters from Cape Fear to 31N...
     Gale Possible Thursday night.

$$

.Forecaster Scovil/Kells. Ocean Prediction Center.



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