000
AGNT40 KWNM 150236
MIMATN

Marine Weather Discussion for N Atlantic Ocean
NWS Ocean Prediction Center Washington DC
936 PM EST Fri Dec 14 2018

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

High pressure will continue to move east to the northeast of the
waters with its ridge extending southwest into the far
southeastern waters in the near short term. Low pressure will
quickly move northeast from the southern states as another high
pressure remains to the north of the region and the resultant
tight pressure gradient has generated gale force winds over the
waters. Latest GOES16 RGB Geocolor satellite images show
relatively thickening warm clouds moving east across the region
but dry airmass is also depicted over the mid west. Scatterometer
retrievals around 2359Z missed most of the forecast region but
indicated stronger winds to the northeast of the Baltimore
Canyon. Latest NCEP weather map has weak low pressure 1024 Mb
over the central waters while strong high pressure 1036 MB is
just east of the northern waters. Pressure gradient has become
tight over the southern waters where maximum winds are in the
gale force range but remains fairly relaxed across the rest of
the waters.

Seas are relatively small across most of the waters except the
southern waters were seas peak at 14 ft the inner waters adjacent
to Georgia and South Carolina. Otherwise, seas range between 2
and 5 ft. Both wave models NWW3 and ECMWFWAVE have matched very
well the seas pattern over the waters and they both agree in the
short term on seas tarting to build form the south as low
pressure approaches the waters. Seas will build to 16 ft and will
keep pushing the peak values northeast across the southern then
into central waters. Forecast NWW3 seas are still relatively
lower than those of ECMWFWAVE. Will stay with ECMWFWAVE for seas.

In the upper levels, at 500 MB level, global models have an
upper level ridge across the waters with some significant energy
embedded in an upper level trough across the mid west. In the
short term, the models suggest hat the energy over the Midwest
will shift east with a bulk of it passing over the southern
states, then lift northeast into the Mid Atlantic states and
enter the central waters. The resultant surface features will be
a strong low pressure moving east and eventually reach the waters
and that will tighten pressure gradient over the waters.

Models GFS/ECMWFHR/UKMETHR/CMC have initialized the synoptic
surface observations fairly well. Models have also agreed in the
short term to continue moving high pressure to the east of the
northern waters and its ridge over the southern waters, east of
the waters. Some differences exist in the extended period as low
pressure approaches the waters mainly on timing and they differ
also on the secondary low pressure that has formed near the
coastal waters ahead of the main low to the southwest. ECMWFHR
has more than two lows popping up along a front while the other
models stick to just two lows. Otherwise, low pressure area will
impact he waters in the extended period and that will keep a
tight pressure gradient that is well supported by the upper level
synoptic features. Will keep consistency and continue to use
ECMWFHR for winds and will retain warning headlines.



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PREVIOUS DISCUSSION...

GOES-E water vapor imagery continues to impress this afternoon,
with broad closed upper low slowly churning E across the Deep
South. Associated cold front and coincident squall line has
pushed into the far eastern Gulf of Mexico this afternoon, and
scattered thunderstorms continue to fire across the far SW
offshore zone ANZ835. Return flow across our southern waters has
steadily increased throughout the day, and earlier ASCAT
overpasses returned widespread 20-30 kt winds across the Gulf
Stream south of about 35N. There were a few embedded gale barbs,
however noted these were co-located in areas of deep convection.
That said, all model guidance initiated these winds poorly at
best, however the broad scale of strong 25+ kt winds were best
handled in the 12z ECMWF. Accordingly, will incorporate the
latest ECMWF into the near term forecast grids, however will make
extensive edits out of deference to forecast continuity and
current gale conditions. This first round of gales ends west to
east across Baltimore Canyon Sat.

Upper low exits offshore the Mid Atlantic coast late Sun, then
slowly tracks NE across the central and northern waters Mon and
Mon night. OPC preference has been nearer to a non-NCEP solution
for the past couple of days, and the operational ECMWF remains
along the NW side of the 12z global consensus and ensemble means.
This is actually preferred with the last 3-4 consecutive cycles
of guidance trending this surface low farther NW. Unfortunately,
the close approximation of the low tucked into the coast results
in a stronger gradient along its north and northwest quadrants,
and based on the low location and trends, will be including gales
in this package just off the Jersey Shore and Long Island from
12z Sun to 00z Mon. Confidence in these gales is only average,
but trending up.

Then for Mon night into Tue night, sharp upper trough digs
quickly SE across Quebec, capturing the upper low along 65W. This
injection of upper support leads to near rapid cyclogenesis of
the surface low near Nova Scotia Mon night into Tue, and behind
the passing secondary cold front, isallobaric gradient wind
response should easily support another round of widespread gales
across all offshore waters north of about 37N, and east of about
73W. Will use a blended solution here between a boosted version
of the 12z ECMWF with the 12z GFS in order to iron out minor
location differences in pockets of strongest winds. Even this
being at the end of the medium range, gale confidence here is
the highest of the entire forecast. High pressure ridge is
expected to build over the W Atlantic Wed and Wed night.

Seas: similar to the wind grids, will be able to generally use
the WAM for most of the forecast period. Do plan on increasing
seas in periods of gales through Sun night, then boost the WAM as
much as 20-25 percent for the strong gales in CAA Mon night and
Tue.

Extratropical Storm Surge Guidance: both the 12z ETOFS and ETSS
paint positive surge values in excess of 1 ft from near Wallops
Island north to Montauk Point during the day Sunday, with highest
values to 1.5 ft along the Jersey Shore into Raritan Bay. With
confidence increasing that the surface low may be tucked closer
into the coast - and onshore gales possible N and NW of the low
center - these guidance values from the surge models may prove
too low. Keep close tabs to your local coastal National Weather
Service office for more forecast details.



.WARNINGS...Preliminary.

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

.NT2 Mid-Atlantic Waters...
.ANZ820...Hudson Canyon to Baltimore Canyon...
Gale Sunday.
Gale Possible Monday night into Tuesday.
.ANZ915...Hudson Canyon to the Great South Channel...
Gale Sunday.
Gale Possible Monday into Tuesday.
.ANZ920...Baltimore Canyon to the Great South Channel...
Gale Saturday.
Gale Possible Sunday night into Tuesday.
.ANZ905...The Great South Channel to the Hague Line...
Gale Possible Sunday night into Tuesday night.
.ANZ910...East of the Great South Channel and south of 39N...
Gale Saturday.
Gale Possible Monday into Tuesday night.
.ANZ828...Inner Waters from Cape Charles Light to Currituck Beach Light...
Gale tonight.
.ANZ925...Outer Waters from Baltimore Canyon to Hatteras Canyon...
Gale tonight into Saturday night.
Gale Possible Monday night into Tuesday.
.ANZ830...Inner Waters from Currituck Beach Light to Cape Hatteras...
Gale tonight.
.ANZ833...Inner Waters from Cape Hatteras to Cape Fear...
Gale tonight.

$$

.Forecaster Musonda/Collins. Ocean Prediction Center.