000
AGNT40 KWNM 230812
MIMATN

Marine Weather Discussion for N Atlantic Ocean
NWS Ocean Prediction Center Washington DC
312 AM EST Thu Jan 23 2020

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

The GOES infrared satellite imagery indicates some remaining
cold air advection across srn NT2 offshore waters this morning
in the tightened pressure gradient between high pressure over the
NT1 offshore waters and strong low pressure SE of the area near
Bermuda. The Ascat wind retrievals from 02Z last night indicated
an area of gale force winds over the outer srn NT2 waters, and
also a small area along the N wall of the Gulf Stream. Current
surface reports still show winds up to 35 kt in the inner NT2
waters, and a Sentinel altimeter pass from around 03Z showed
winds to 30 kt just NW of the current report of 35 kt. All of the
00Z model winds are initialized low when compared with the
current data, with values up to 10 kt low in most of the models.
However, the models indicate that the winds should weaken early
this morning with the low moving off to the E which will allow
the pressure gradient to weaken. As a result, am expecting all
gales to shift E of the offshore waters by 12Z this morning, with
about average confidence, so planning on allowing all gale
headlines from last night to expire at that time. The models
indicate that the gales will continue to the E of the offshore
waters going into Fri, so planning on stay near the previous
grids up to that point since they are generally well supported
by the 00Z models.

The 00Z models then remain in good overall agreement through the
remainder of the forecast period, starting with high pressure
persisting across the W Atlc and the offshore zones into Sat. The
models then indicate a strong cold front will move into the W
Atlc late Sat into Sun as the associated low center tracks NE
along the New England coast. There are some slight timing
differences between the 00Z GFS and the ECMWF, with the rest of
the global models near the two solutions. There is also a
fairly strong signal for the development of gales ahead of the
front in the southerly flow over NT1 on Sat night and Sun.
Although the cooler SSTs in NT1 normally creates a hurdle for
stronger winds aloft to mix down in warm advection as they
typically generate an inversion near the surface, the
anomalously warm SSTs with values 3+ degrees Fahrenheit above
the historical values should allow for a weaker inversion. In
addition, the guidance indicates a strong low level jet will
develop just ahead of the boundary which will increase the
vertical shear and turbulent mixing. As such, the prospect for
gales seems reasonable, and model soundings support this idea
with GFS mixed layer winds showing marginal gales. As a result,
am planning on keeping previous warning headlines with average
confidence in the next package. As for the wind grids, am
planning on using a blend of the 00Z GFS 10m/first sigma winds
with the bias corrected 00Z ECMWF winds from Sat 00Z through the
end of the forecast period.

.Seas...A 03Z Sentinel altimeter overpass indicated wave heights
to 19 ft along the N wall of the Gulf Stream in srn NT2, while a
06Z surface observation approximately 120 nm S of Cape Fear
indicated seas to 21 ft very close to the altimeter overpass. The
00Z Wavewatch and ECMWF WAM are initialized extremely low in this
region when compared with the data, with values in the guidance
roughly 9 ft low. Since the previous grids are initialized
somewhat better, am planning on starting out with them. However,
will still need to make some large adjustments. Will continue
with the previous grids into Fri night, then switch to a blend of
the 00Z Wavewatch and ECMWF WAM as a compromise to the small
differences between the two models through the end of the
forecast period.

.EXTRATROPICAL STORM SURGE GUIDANCE...The 00Z surge models are
showing positive values ranging between 0.5 to 2 ft along the SE
coast today into Fri with the NE flow along the far SE coast.
This may be a tad underdone with the underdone GFS winds proving
the forcing for the surge models. Water level observations along
the Southeast US are about 0 to 0.5 ft higher than the predicted
levels this afternoon, suggesting that the latest ETSS and
ESTOFS are still a bit underdone with the surge. Another positive
surge may develop further N from the Delmarva northward to
southern New England Fri night into the weekend as onshore winds
increase over this region with the another strong low pressure
system moving into the area over the weekend. The 00Z ESTOFS and
ETSS are both showing values in excess of 1.5 ft in the NY Bight
area with the SE flow ahead of the system. For more detailed
information, follow the latest forecasts issued by your local
National Weather Service forecast office.

.WARNINGS...Preliminary.

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

.NT2 Mid-Atlantic Waters...
.ANZ915...Hudson Canyon to the Great South Channel...
Gale Possible Saturday night.
.ANZ905...The Great South Channel to the Hague Line...
Gale Possible Saturday night.
.ANZ910...East of the Great South Channel and south of 39N...
Gale Possible Saturday night.

$$

.Forecaster Kells. Ocean Prediction Center.