Marine Interpretation Message
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000
AGNT40 KWNM 170811
MIMATN

Marine Weather Discussion for N Atlantic Ocean
NWS Ocean Prediction Center Washington DC
311 AM EST Sat Nov 17 2018

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

Over the short term, today into Mon, the 00Z guidance is in good
agreement over the waters with strong low pressure moving NE
away from the region as high pressure builds E toward the region
in the wake of the low. ASCAT overpasses between 0040Z and 0225Z
last evening still indicated fairly widespread gales occurring
over eastern NT1 and NE NT2 waters, with these gales lining up
with the ongoing OPC forecast. These gales are forecast to shift
E of the waters around 9-10Z this morning. Otherwise, no hazards
are likely over the region into Mon. A weak secondary cold front
is still forecast to pass SE over New England waters tonight,
and then dissipate Sun. High pressure will cover most of the
region Sun into Sun night, with the high moving off to the E of
the waters later Sun night into Mon with weak low pressure and
an associated cold front developing over the New England waters.
For the early morning package, we will populate winds with a
50-50 blend of the previous grids and 00Z high resolution Warw
winds for today through Sun, with little change from the past
few OPC forecasts. For Sun night into Mon we will transition
more toward the 00Z ECMWF winds with the 00Z ECMWF a good
compromise in the guidance. Forecast confidence is slightly
above average over the area today into Mon.

Over the medium range, we will continue to populate our winds
with the 00Z ECMWF guidance, except to use the boost tool, which
will raise winds up to 15 percent, over and E of the gulf stream
Mon night into Tue night over the waters. This will allow for a
period of gales to develop Tue night in the wake of a cold front
and low pressure area moving E and NE of the waters, over the
far NE NT2 waters, or zones ANZ905-910, with both the 00Z GFS
and 00Z UKMET trending more toward the 00Z ECMWF solution at
that time. Confidence in these gales is near average with some
added confidence as they would occur near the north wall of the
gulf stream later Tue night. The low will then move NE away from
the waters during Wed, with winds capped at 20 kt for now as a
weak high pressure ridge quickly crosses the area. A cold front
will approach from the NW by early Wed evening, then cross the
area overnight Wed into Thu. As there remains differing
solutions regarding both the timing and strength of this front
we will cap winds at 25 kt over the waters later in the forecast
period, and make additional adjustments to the forecast over the
next few days once better model agreement develops. Forecast
confidence falls to below average over the waters Wed and Wed
night. Please closely monitor the latest OPC forecasts over the
next few days as there is the potential for more widespread
gales developing by Wed night and beyond.

Seas...Both the 00Z Wavewatch and 00Z ECMWF WAM appear to have
initialized fairly well over the waters early this morning. For
the early morning package, we will use a 50/50 blend of these
two wave models today into Mon, rely more on the WAM guidance
later Mon into Wed to match the winds, and then use a 70 percent
WAM/30 percent Wavewatch blend later in the forecast period in
an attempt to match the adjusted wind forecast as noted above.
Some manual edits will also be made in deference to nearby
coastal WFO and TAFB grids, and to better match the wind
forecast especially later in the forecast package.

.EXTRATROPICAL STORM SURGE GUIDANCE...No significant positive
surge events appear likely over the region during the next 3-5
days.

.WARNINGS...Preliminary.

.NT1 New England Waters...
     None.

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

$$

.Forecaster Mills. Ocean Prediction Center.


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