000
AGNT40 KWNM 170715
MIMATN

.Marine Weather Discussion for N Atlantic Ocean
.NWS Ocean Prediction Center Washington DC
215 AM EST SUN 17 DEC 2017

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

The 0120 UTC and 0200 UTC Ascat overpasses continued to indicate
northwest gales across the offshore waters south of Nantucket,
across Georges Bank, and over the northern outer NT2 waters. As
has been the case for the last 12 to 18 hours, the GFS first
sigma level winds are still the best initialized in the ongoing
cold air advection offshore. Even the high resolution HRRR`s
surface winds were well underdone with the gales when compared
to the Ascat data. The 4km NAM was somewhat better, but still
did not Based on the latest guidance will be extending the gale
warnings across the outer ANZ905 and ANZ910 zones to 12Z. The 00
UTC GFS and 00 UTC NAM are consistent that the gales should
shift east of the eastern most offshore zones shortly after
daybreak.

The 00 UTC models are consistent that relatively weak gradients
and surface winds will occur across the offshore waters later
today through Tue, with the upper level flow becoming more zonal
than has been the case over the last week or so. The reinforcing
secondary cold front across the northern NT2 waters will stall
and weaken off the Delmarva Peninsula today, with the models all
indicating a weak surface low will develop and slowly move east
along the front tonight and Mon. The developing low should pull
the weak front south to near Cape Fear Mon before it again
stalls and dissipates Mon night/Tue. Once this mornings gales
shift east of the waters, we have well above average forecast
confidence that the offshore winds will remain below any warning
criteria through Mon night.

The latest models then share a similar timing with another cold
front forecast to move off the northern mid-Atlantic and New
England coasts Tue night. Over the past 24 to 36 hours, the
models have not been very consistent with how amplified the
associated upper level trough will be across New England Tue
night and Wed. Versus its previous two to three runs, the 00 UTC
GFS was again somewhat stronger with the post frontal winds
across the New England and northern Mid Atlantic waters Tue
night and Wed. The 00 UTC UKMET also was slightly stronger than
its 12 UTC/16 run. The past few runs of the ECMWF have all
indicated a some potential for marginal gales Tue night/Wed at
least across the offshore waters generally east of 69W and north
of 39N. Given the run to run model variability, will be keeping
continuity and maintaining some marginal gales Tue night/Wed
across the zones listed below in the warnings summary section.
The models are then consistent that a southern stream low will
develop and move off the southern Mid Atlantic coast late Wed
and Wed night, with the 00 UTC GFS/ECMWF/UKMET all advertising
associated winds as high as 30 kt across the waters south of
Cape Hatteras. Also, the 00 UTC GFS trended toward the slower
ECMWF, and this slower solution is well supported by the latest
GEFS and ECMWF EPS means.

.Seas: NOAA buoy 44011 near Georges Bank reported 16 ft and 14
ft at 05 UTC and 06 UTC respectively, indicating seas have been
building across these outer waters over the past few hours.
Also, the slightly higher 00 UTC ECMWF WAM is now better
initialized than the 00 UTC Wavewatch III with these higher
seas. A 3:1 ECMWF WAM to WW3 blend seems to match the current
observations well. Will be populating the wave height grids with
this blend throughout the forecast period, given our general
preference for the ECMWF winds.

Extratropical Storm Surge Guidance: No major deviation from the
latest guidance appears needed at this time, with little chance
for any significant positive surge along the east coast over the
next few days.

.WARNINGS...Preliminary.

.NT1 New England Waters...
.ANZ800...Gulf of Maine...
Gale Possible Tuesday night into Wednesday.
.ANZ805...Georges Bank west of 68W...
Gale Possible Wednesday.
.ANZ900...Georges Bank east of 68W...
Gale Possible Tuesday night into Wednesday.

.NT2 Mid-Atlantic Waters...
.ANZ905...The Great South Channel to the Hague Line...
Gale today.
Gale Possible Tuesday night into Wednesday.
.ANZ910...East of the Great South Channel and south of 39N...
Gale today.

$$

.Forecaster Clark. Ocean Prediction Center.