Marine Interpretation Message
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000
AGNT40 KWNM 191347
MIMATN

Marine Weather Discussion for N Atlantic Ocean
NWS Ocean Prediction Center Washington DC
847 AM EST Fri Jan 19 2018

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

At 12z a high pressure ridge was located across the offshore NT1
and NT2 waters. Strong low pressure that had been impacting the
region continued to pull away to the east and was located near
40N58W. With the 06z GFS/NAM in good agreement through the near
term see no reason to make major adjustments to the ongoing
forecast. Low pressure that brought warning headlines to the
offshore waters continues to pull away to the east as mentioned
earlier. Hence warning headlines in place in the prior forecast
will be allowed to expire to start this forecast. Continue to
anticipate brief period of gales in the northern NT1 waters
Saturday as strong low pressure swings by to the north through
Eastern Canada. Beyond that next opportunity for gales will be
Tuesday night into Thursday as winds increase ahead of a strong
cold front expected to move through the waters.

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

Earlier ASCAT overpasses confirmed trends seen in Goes-16 Air
Mass imagery, with strongest storm force wind returns now along
the south and southeast quadrants coincident with PV anomaly and
jet streak. Near term higher resolution guidance from the 00z
NAM and 05z HRRR pull associated gale force winds outside of the
OPC forecast area in the next couple of hours as the low
continues moving quickly off to the NE at about 30 kt. This is
well represented in the ongoing OPC grids, and will allow
headlines to expire across the outer zones ANZ905 and ANZ910 with
next forecast issuance.

Sat and Sat night: as alluded to in the previous discussion,
guidance initially trended stronger through the day yesterday,
then remained fairly consistent in the 00z cycles with strong
gradient south of approaching cold front over the far northern
waters Sat afternoon. With high pressure settled over the
southern zones, guidance continues to suggest a gradient
supportive of minimal gale headlines generally north of about
40N. With nearly unidirectional winds and excellent agreement
with the timing of the front, was able to use an even blend
between the GFS first sigma level, UKMET, and NAM to produce
desired coverage of winds and minimal gales. These hazards will
be brief (18z to 00z). Confidence is slightly above average.

Sun onwards, trended grids to previous forecast which preferred
the timing of the ECMWF as another strong cold front moves across
OPC waters. With the 00z run comparing favorably to the previous
12z cycle, see no reason to make changes to the ongoing forecast
already in place. Gale headlines will remain in the forecast
beginning around 18z Tue.

Seas: opted to use the WW3 through late Sat night to better match
the OPC wind grids, however did increase values to ensure seas
increased to 12 ft during periods of gales. Trended forecast to
previous grids / 12z ECMWF WAM thereafter.

Extratropical Storm Surge Guidance...no major deviation from the
latest surge guidance appears necessary through the forecast
period.


.WARNINGS...Preliminary.

.NT1 New England Waters...
.ANZ800...Gulf of Maine...
     Gale Saturday.
     Gale Possible Tuesday into Tuesday night.
.ANZ805...Georges Bank west of 68W...
     Gale Saturday.
     Gale Possible Tuesday.
.ANZ900...Georges Bank east of 68W...
     Gale Saturday.

.NT2 Mid-Atlantic Waters...
.ANZ920...Baltimore Canyon to the Great South Channel...
     Gale Possible Tuesday into Tuesday night.
.ANZ905...The Great South Channel to the Hague Line...
     Gale Saturday.
     Gale Possible Tuesday night.
.ANZ910...East of the Great South Channel and south of 39N...
     Gale Possible Tuesday night.
.ANZ925...Outer Waters from Baltimore Canyon to Hatteras Canyon...
     Gale Possible Tuesday into Tuesday night.

$$

.Forecaster Holley/Collins. Ocean Prediction Center.



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