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AGNT40 KWNM 211958
MIMATN

Marine Weather Discussion for N Atlantic Ocean
NWS Ocean Prediction Center Washington DC
358 PM EDT Sat Jul 21 2018

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


Near term through 18z Sun...GOES-E visible imagery continues to
impress this afternoon, with a still intensifying low pressure
now centered over northeastern NC per the 18z coordinated OPC-
WPC surface analysis. Widespread convection continues to fire in
the tropical moisture plume streaming north across the central
and southern waters, evidenced by the overshooting tops and
lightning strike density data. Perhaps most concerning is the new
convection firing off the VA/NC coasts; would not be surprised
to see storm force gusts within or near any of these showers and
storms. ASCAT overpasses unfortunately whiffed on the W Atlantic
this afternoon, with the most interesting and suspect wind areas
directly within the nadir gaps. We did get forecast validation
from buoy 41025, however, which is located just SE of Cape
Hatteras; earlier in the day winds peaked (8-min average) at 33
kt with gusts to 41 kt. For the afternoon wind grids, out of
deference to some of the stronger and west trends from the
regional guidance, plan to incorporate some of the higher 30m 12z
GFS winds into the grids. Realistically this will not change the
headlines or forecast too much, but primarily serve to continue
expanding the gales within the grids slightly W, while also
expanding the areal coverage of the strongest 40-45 kt winds.
Gales will reach the Jersey shore and western Long Island by 00z
this eve, then diminish below warning threshold by 09z tonight as
the low moves well inland and fills across upstate NY. Worth
mentioning again that higher gusts exceeding storm force are
certainly possible in or near any of the stronger thunderstorms
this evening and overnight.

18z Sun through the end of the period...strong high pressure over
the W Atlantic gradually drifts W towards the offshores,
delivering persistent southerly winds across most of the OPC
waters. Strongest S-SE winds will be Sun into Mon night -
generally in the 20 to 30 kt range - slowly easing from NE to SW
as the high noses farther west toward the offshores and the
gradient weakens. Winds turn more S-SW by late Wed and into Thu
as upper trough moves east across southern Canada, with a frontal
boundary slowly approaching the W Atlantic. 12z models and
ensembles remain in good agreement throughout the medium range,
and out of deference to OPC forecast continuity, plan to run a
1:1 blend between the 00z/12z ECMWF for the representative wind
grids this afternoon.

Seas: at 18z the WW3 was performing better than the WAM, with
highest seas to 14 feet already off the coast of the Outer Banks.
Prefer the higher values from the WW3 into Sunday, which now
increase to about 16 ft in response to strong gales overnight.
These are 1-2 ft higher than the WAM, and are well supported by
12z GWES guidance. After late Sunday, similar to the wind grids,
plan to transition seas to a blend with the most recent 2 runs of
the WAM.

Extratropical Storm Surge Guidance: 12z ESTOFS guidance
indicates positive surge 1.0 to 2.0 ft (and possibly higher)
across the Delmarva, Jersey Shore, and western Long Island by
00z this eve, with a max between 00z-06z in Raritan Bay. The
ESTOFS has been remarkably consistent for the past several runs
showing this scenario, and continues to output higher values
compared to the 12z ETSS. Would continue to favor the higher
ESTOFS values this evening and overnight.

Please continue to closely monitor the latest forecasts and
advisories from the local coastal National Weather Service
offices.

.WARNINGS...Preliminary.

.NT1 New England Waters...
.ANZ815...South of Long Island...
Gale tonight.

.NT2 Mid-Atlantic Waters...
.ANZ820...Hudson Canyon to Baltimore Canyon...
Gale today into tonight.
.ANZ915...Hudson Canyon to the Great South Channel...
Gale tonight.
.ANZ920...Baltimore Canyon to the Great South Channel...
Gale today into tonight.
.ANZ825...Inner Waters from Baltimore Canyon to Cape Charles Light...
Gale today into tonight.
.ANZ828...Inner Waters from Cape Charles Light to Currituck Beach Light...
Gale today.
.ANZ925...Outer Waters from Baltimore Canyon to Hatteras Canyon...
Gale today into tonight.
.ANZ830...Inner Waters from Currituck Beach Light to Cape Hatteras...
Gale today.
.ANZ833...Inner Waters from Cape Hatteras to Cape Fear...
Gale today.
.ANZ930...Outer Waters from Hatteras Canyon to Cape Fear...
Gale today into tonight.

$$

.Forecaster Collins. Ocean Prediction Center.