Marine Interpretation Message
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000
AGNT40 KWNM 122022
MIMATN

Marine Weather Discussion for N Atlantic Ocean
NWS Ocean Prediction Center Washington DC
322 PM EST Tue Dec 12 2017

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

A complex low pressure system over the eastern Great Lakes and
western New England will move NE tonight with an associated
strong cold front sweeping E and SE over the offshore waters. A
1523Z ASCAT overpass indicated a large area of SW winds up to 30
kt or so over NT2 waters and S and SE winds to 25 kts over NT1
waters. There were a couple of 35 kt barbs near the edge of the
pass over central NT2 waters which may have been impacted by a
few thunderstorms in that region this morning.

Over the short term, we will refresh the grids and forecast
using the 12Z GFS tonight into Thu night (using the stability
tool with places the stronger first-sigma layer winds over the
unstable waters and slightly lower 10 meter winds over the
stable waters) as it fits the ongoing forecast and latest
observations rather well, and is in good agreement with non-GFS
models over the next few days. This will lead to gale force
winds developing over all offshore waters tonight into Wed, with
storm force winds developing over far NE NT2 waters later
tonight as the strong front passes E over these waters which are
near the north wall of the gulf stream. Thunderstorms have
become fairly widespread this afternoon and extend from NE NT2
waters or just S of Georges Banks SW over the outer portion of
the central NT2 waters, E of Cape Hatteras. Thunderstorms will
remain likely over this region into tonight near and ahead of
the strong cold front. Caution for strong wind gusts near and
exceeding gale to storm force and very rough seas in and near
the stronger thunderstorms tonight. Conditions will only improve
briefly Wed night ahead of the next low pressure system that
will impact the waters Thu as it tracks E along 40N or so. This
system will allow gales to return to central and northern NT2
waters Thu into Thu night, with a period of storm force winds
over NE NT2 waters once again by 18Z Thu or so. The 12Z GFS
backed-off on these winds slightly so we have manually forced
them back into the forecast as the 12Z GFS may be a little
underdone regarding winds over these waters at that time.
Confidence levels are somewhat above average over the region
tonight through Thu night with decent model agreement through
this period.

For Fri through Sat night, we will use a 50-50 blend of the 12Z
GFS stronger first sigma layer winds and 12Z ECMWF guidance over
the region, as yet another developing low passes NE over the
region. This blend will also tend to maintain gales as was noted
in the previous few OPC forecasts, with confidence levels near
average with gales developing over only NT2 waters Fri night
into Sat night. For Sun and Sun night, we will transition the
offshore forecast toward the 12Z ECMWF guidance as high pressure
moves E over the waters Sun, passing E of the waters Sun night as
this solution appears to fit rather well with the latest medium
range guidance from WPC. The next cold front will approach the
region from the W Sun night. For now, we will keep winds below
gale force for Sun night as this is the very end of the forecast
package, and we would prefer better model agreement before adding
any hazards to the forecast.

.Seas...The latest observations indicate the the 12Z Wavewatch
may be a little too low initially, while the 12Z ECMWF WAM is a
little too high. The previous grids and forecast appear to be
close to the initial conditions over the waters this afternoon.
For the afternoon package we will rely on the previous grids and
forecast for tonight into Thu night, transition to a 50/50 blend
of the Wavewatch and WAM by Fri into Sat night, and then use a 75
percent WAM/25 percent Wavewatch blend thereafter, as we lowered
the winds from the ECMWF guidance late in the period, and this
blend will lower the sea heights forecast somewhat which will
better match the wind forecast.

.EXTRATROPICAL STORM SURGE GUIDANCE...No significant issues with
the latest surge guidance is noted at this time.

.WARNINGS...Preliminary.

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

.NT2 Mid-Atlantic Waters...
.ANZ820...Hudson Canyon to Baltimore Canyon...
     Gale tonight into Wednesday.
     Gale Thursday.
.ANZ915...Hudson Canyon to the Great South Channel...
     Gale tonight into Thursday.
     Gale Possible Saturday.
.ANZ920...Baltimore Canyon to the Great South Channel...
   Gale into Thursday. Gale Possible Friday night
   into Saturday night.
.ANZ905...The Great South Channel to the Hague Line...
     Storm tonight.
     Gale Wednesday into Wednesday night.
     Storm Thursday.
     Gale Possible Thursday night.
     Gale Possible Saturday into Saturday night.
.ANZ910...East of the Great South Channel and south of 39N...
     Gale late today.
     Storm tonight.
     Gale Wednesday into Wednesday night.
     Storm Thursday.
     Gale Possible Thursday night.
     Gale Possible Saturday into Saturday night.
.ANZ825...Inner Waters from Baltimore Canyon to Cape Charles Light...
     Gale tonight into Thursday.
.ANZ828...Inner Waters from Cape Charles Light to Currituck Beach Light...
     Gale late today into Thursday.
.ANZ925...Outer Waters from Baltimore Canyon to Hatteras Canyon...
     Gale late today into Thursday.
     Gale Possible Friday night into Saturday.
.ANZ830...Inner Waters from Currituck Beach Light to Cape Hatteras...
     Gale late today into Thursday.
.ANZ833...Inner Waters from Cape Hatteras to Cape Fear...
     Gale late today into tonight.
     Gale Wednesday night into Thursday.
.ANZ930...Outer Waters from Hatteras Canyon to Cape Fear...
     Gale late today into Thursday.
     Gale Possible Friday night.
.ANZ835...Inner Waters from Cape Fear to 31N...
     Gale late today into tonight.
.ANZ935...Outer Waters from Cape Fear to 31N...
     Gale late today into tonight.
     Gale Possible Friday night.

$$

.Forecaster Mills. Ocean Prediction Center.


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