Marine Interpretation Message
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000
AGNT40 KWNM 220140
MIMATN

Marine Weather Discussion for N Atlantic Ocean
NWS Ocean Prediction Center Washington DC
840 PM EST Sun Jan 21 2018

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

The preliminary 00Z OPC surface analysis indicated a weak cold
front east of the central NT2 waters, another front stalling
over the Gulf of Maine, and high pressure over the southern NT2
waters. The 18Z model guidance suggests that little change is
needed to the ongoing OPC grids and forecast for the evening
update. The main forecast concern will be the widespread gales
expected to develop Tue and Tue night over the waters as a
strong cold front crosses the region. Any adjustments to the
previous hazards will not be made until we can fully evaluate
all of the 00Z guidance once it arrives overnight. For the
evening update, we will make only a few minor tweaks to the
previous grids and forecast to align the grids with the latest
observations, and nearby coastal WFO and TAFB grids and
forecasts prior to forecast issuance this evening.

For seas, again little change appears necessary for the evening
update with sea heights ranging from 1 to 3 feet over western
portions of the offshore waters, to near 6 feet over the far
outer NE NT2 waters.

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PREVIOUS DISCUSSION...

The 12Z models were reasonably well initialized with the
offshore winds this morning. The 14Z and 15Z Ascat overpasses
indicated only two limited areas with winds to 20 kt, across the
Gulf of Maine and the outer ANZ910 waters associated with the
two weak cold/stationary fronts. Elsewhere across the offshore
waters Ascat had retrievals of 15 kt or less.  Versus their
respective previous runs, the 12Z models were generally
consistent with their respective previous runs and remain in
good agreement for the next few days with the synoptic pattern
across the west Atlantic. The southern cold front which at 18Z
extended across the central NT2 waters to the Virginia tidewater
area will continue to drift south tonight and eventually
dissipate Mon. The latest models are also consistent that the
cold front off the downeast Maine coast will move south this
evening, then stall near Cape Cod late tonight and Mon before
lifting back north across the waters as a warm front Mon night.
Winds are not expected to substantially increase until late Mon
night and Tue as a strong cold front approaches the New England
/Mid-Atlantic coasts Tue and passes east across the area Tue
night. The 12Z models are generally consistent that an upper
level low will move east across the Ohio valley Tue and lift
northeast across New England Tue night, supporting a developing
surface low and the strong cold front. We have increasing
confidence with the gales which are forecast Tue/Tue night ahead
of the cold front across the outer offshore waters. The 12Z
models are all on board with these hazards. The 12Z GFS and 12Z
ECMWF both show a 50 to 70 kt low level jet developing across the
offshore waters north of Hatteras Canyon, which should be more
than sufficient to get some gales to mix to the surface
especially across the warmer NT2 waters. Based on the latest
guidance, will also expand the gales to include the inner zones
from Cape Fear to Cape Charles as well as zone ANZ930. The front
and associated gales are expected to pass east of the offshore
waters late Tue night. Confidence with the gale hazards is well
above average.

Over the medium range, a secondary cold front will then move SE
over NT1 and northern NT2 waters later Wed and Wed night,
followed by high pressure slowly building E toward the region
Thu and Thu night. The past couple runs of the ECMWF and UKMET
were somewhat more emphatic with surface low development just
east of the northern NT2 waters Thu. The GFS indicates the
development east of the ECMWF/UKMET positions, however does
share the similar strong northwest winds across the northern
outer NT2 waters. Versus its previous run, the 12Z GFS trended
stronger with these northwest winds. Given the 12Z guidance,
chances for these winds reaching gale force are better mainly
near the Gulf Stream across ANZ925, ANZ920 and ANZ910. However,
will wait for more run to run consistency from the GFS before
adding any gales. By Fri/Fri night, models are consistent in
moving the high pressure ridge to the coast and then offshore.


Seas: The 12Z ECMWF WAM and 12Z Wavewatch are a foot low across
the eastern NT1 waters this afternoon, but elsewhere are well
initialized with the offshore/coastal wave heights. The guidance
is in excellent agreement through Mon night, then the ECMWF WAM
builds seas more rapidly and higher than the WW3 Tue and Tue
night. For the wave height grids Tue through Thu night, will be
blending the past two runs of the ECMWF WAM. Then from Fri
through the remainder of the forecast, will use an even blend of
the 12Z WW3 and 12Z ECMWF WAM.

.EXTRATROPICAL STORM SURGE GUIDANCE...No major deviation from
the latest surge guidance appears necessary over the next few
days across the region.

.WARNINGS...Preliminary.

.NT1 New England Waters...
.ANZ800...Gulf of Maine...
     Gale Possible Tuesday into Tuesday night.
.ANZ805...Georges Bank west of 68W...
     Gale Possible Tuesday into Tuesday night.
.ANZ900...Georges Bank east of 68W...
     Gale Possible Tuesday into Tuesday night.
.ANZ810...South of New England...
     Gale Possible Tuesday into Tuesday night.
.ANZ815...South of Long Island...
     Gale Possible Tuesday.

.NT2 Mid-Atlantic Waters...
.ANZ915...Hudson Canyon to the Great South Channel...
     Gale Possible Tuesday into Tuesday night.
.ANZ920...Baltimore Canyon to the Great South Channel...
     Gale Possible Tuesday into Tuesday night.
.ANZ905...The Great South Channel to the Hague Line...
     Gale Possible Tuesday night.
.ANZ910...East of the Great South Channel and south of 39N...
     Gale Possible Tuesday night.
.ANZ828...Inner Waters from Cape Charles Light to Currituck Beach Light...
     Gale Possible Tuesday.
.ANZ925...Outer Waters from Baltimore Canyon to Hatteras Canyon...
     Gale Possible Tuesday into Tuesday night.
.ANZ830...Inner Waters from Currituck Beach Light to Cape Hatteras...
     Gale Possible Tuesday.
.ANZ833...Inner Waters from Cape Hatteras to Cape Fear...
     Gale Possible Tuesday.
.ANZ930...Outer Waters from Hatteras Canyon to Cape Fear...
     Gale Possible Tuesday into Tuesday night.

$$

.Forecaster Mills/Clark. Ocean Prediction Center.



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