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000
AGNT40 KWNM 201354
MIMATN

Marine Weather Discussion for N Atlantic Ocean
NWS Ocean Prediction Center Washington DC
954 AM EDT Sun May 20 2018

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

The preliminary 12Z OPC-NCEP surface analysis shows a broad
south and southwesterly flow over the waters this morning, with
a warm front extending S and SE from eastern Nova Scotia, and a
pair of cold fronts over western New England and the Great
Lakes. The 06Z GFS is very similar to the 00Z cycle which was
used for the ongoing forecast. For the morning update we will
only adjust grids slightly in deference to adjacent coastal WFO
grids and TAFB grids, and also fit the grids to conditions
observed right before issuance time later this morning. The
latest GOES visible satellite imagery, and radar and lightning
data show scattered showers and a few thunderstorms off the SE
U.S. coast with areas of rain over southern New England waters
and E of the Delmarva coast. The latest SREF thunderstorms
guidance shows the highest threat for thunderstorms off the SE
coast today, and with the cold front crossing the area tonight
into Mon. Locally very gusty winds and very rough seas are
possible in and near any of the heavier thunderstorms, with
winds potentially near gale force or higher in the stronger
thunderstorms into Mon.

Seas...Sea heights will be adjusted to fit an altimeter pass
from earlier this morning which indicated seas up to 9 feet off
the mid-Atlantic coast. Otherwise, only minor adjustments will
be made for the morning update mainly to align OPC sea height
forecasts with nearby coastal WFO and TAFB gridded sea heights
over the region during the next few days.

-----------------------------------------------------------------
PREVIOUS DISCUSSION...

High pressure will remain anchored to the east of the southern
waters and that will maintain a weak ridge across the southern
waters while weak fronts will pass over the northern waters and
pressure gradient will remain fairly relaxed through the forecast
period. GOES 16 RGB Satellite images still show few cloud
clusters over most of the region except North of 40N. Convective
clouds are still inland along the coasts from the south eastern
states into the Virginia coast. The NCEP map at 06Z has a
stationary front across the north waters along 40N that extends
inland. Area of high pressure with several centers is still east
of the region and a ridge extends into most of the central and
southern waters which is in line with the latest satellite
images. Pressure gradient is fairly relaxed and observed maximum
winds are only 25 kt in a few areas.

At 500 MB, an upper level ridge cover the region with a short
wave just north of the great lakes with some energy that will
pass east across the northern waters. Models also show that a few
more short waves with some energy will pass through the northern
waters during the forecast period. The low lever jet will remain
to the north of the region and that will keep most of the shear
to the north denying any energy to reach the waters. As such,
pressure gradient must remain relaxed across the region keeping
winds below gale force threshold.

The global models GFS/ECMWFHR/UKMETHR/CMC have initialized
fairly well the 06Z surface observations. In the short term, the
models are in a good agreement on keeping high pressure anchored
to the east of the southern waters with a weak ridge across the
central and southern waters. In the extended period there is an
uncreased chance of energy moving into the northern waters that
will start to tighten the pressure gradient over the NT1 waters
and the Baltimore Canyon. The global models differ slightly in
the extended period on the orientation of a low pressure trough
that will be associated with a low that will pass north of the
region. Otherwise, the general synoptic pattern will remain the
same and so will keep consistency with previous model choice and
stay with GFS.

.SEAS...They are over 6 ft over the southern waters with a peak
at 7 ft while seas are less than 6 ft over the rest of the
region with smallest seas at 3 ft over the far north of the maine
waters. NWW3 and ECMWFWAVE models fit well the 06Z observed seas
pattern. Both wave models also agree in the short term on
slightly building seas over the northern waters to peak at 9 ft.
The variations in the wave model solution in the extended period
are very dismal and so will keep consistency and stay with a
50/50 blend for the seas.


.EXTRATROPICAL STORM SURGE GUIDANCE...n/a.


.WARNINGS...Preliminary.

.NT1 New England Waters...
     None.

.NT2 Mid-Atlantic Waters...
     None.

$$

.Forecaster Mills/Musonda. Ocean Prediction Center.


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