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750
AGNT40 KWNM 161951
MIMATN

.Marine Weather Discussion for N Atlantic Ocean
.NWS Ocean Prediction Center Washington DC
250 PM EST TUE 16 JAN 2018

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

We did not have any Ascat data near the weak surface low east of
Cape Hatteras this morning, which makes it difficult to
determine how the models are initializing this feature. The 12Z
models are generally in good agreement that the low will slowly
strengthen tonight and Wed, as it tracks northward through the
waters toward western Long Island and Cape Cod. The previous
wind grids, which were based on a blend of the GFS first sigma
level and ECMWF 10m winds, still look reasonable. Will continue
to include some limited areas of 30 kt winds across the east
quadrant of the low over the northern NT1 zones and the Gulf of
Maine, which is supported by the 12Z GFS and 12Z 4km NAM. The
latest models then all forecast a sharply amplified upper level
trough to move to the southeast US coast late Wed and move east
across the Mid- Atlantic waters Wed night and Thu. There
continues to be some differences between the models mainly with
the associated surface low development and the strength of the
winds behind the secondary cold front. The UKMET and Canadian
GEM have consistently been a strong outliers, and this continued
with the 12Z runs. The ECMWF has shown the most run to run
consistency over the past couple days and continues to offer a
compromise between the stronger UKMET/GEM and weaker GFS. Made
some changes to the gale hazards based on the 12Z ECMWF and 12Z
4km NAM to include ANZ830 and ANZ833 late Wed night. Also, will
be dropping the gales across ANZ920 as the recent models
indicated a southward shift in the axis of strongest winds.
Given the negative low level lapse rates acros the Gulf Stream,
will adjust the ECMWF winds higher by about 5 to 10 percent Wed
night and Thu. Confidence remains above average with the gale
hazards.

The 12Z models then forecast a high pressure ridge to move off
the southeast US coast Thu night/Fri and remain quasi-stationary
along 30N/31N through Sun. The guidance is also relatively
consistent that as a cold front drops south into New England,
west to southwest winds will increase to 25 kt or 30 kt across
all the offshore waters north of Baltimore Canyon late Fri night
and Sat. The front is expected to then stall and weaken across
the northern NT2 waters Sat night and Sun.

Seas...The 12Z ECMWF WAM and 12Z Wavewatch III are generally
well initialized with the west Atlantic wave heights this
afternoon. Versus its previous run, the 12Z ECMWF WAM was
slightly lower with the highest seas associated with the gales
across the southern NT2 zones Wed night and Thu. As would be
expected with the GFS being weaker with these northwest winds,
the 12Z WW3 is 3 to 5 ft lower than the 00Z/12Z ECMWF WAM. Will
populate the wave height grids with an even blend of the 00Z/12Z
ECMWF WAM through Thu night, then transition solely to the 12Z
ECMWF WAM thereafter, which will match our preference for the
ECMWF winds during the medium range.

Extratropical Storm Surge Guidance...No major deviation from the
latest surge guidance appears necessary through the forecast
period as offshore flow will generally be predominant.

.WARNINGS...Preliminary.

.NT1 New England Waters...
     None.

.NT2 Mid-Atlantic Waters...
.ANZ925...Outer Waters from Baltimore Canyon to Hatteras
Canyon...
     Gale Wednesday night into Thursday.
.ANZ830...Inner Waters from Currituck Beach Light to Cape
Hatteras...
     Gale Wednesday night.
.ANZ833...Inner Waters from Cape Hatteras to Cape Fear...
     Gale Wednesday night.
.ANZ930...Outer Waters from Hatteras Canyon to Cape Fear...
     Gale Wednesday night into Thursday.
.ANZ935...Outer Waters from Cape Fear to 31N...
     Gale Wednesday night into Thursday.

$$

.Forecaster Clark. Ocean Prediction Center.



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