Marine Interpretation Message
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AGPN40 KWNM 202006

Marine Weather Discussion for N Pacific Ocean
NWS Ocean Prediction Center Washington DC
106 PM PDT Sun Aug 20 2017

.FORECAST DISCUSSION...Major features/winds/seas/significant
.weather for the North Pacific N of 30N and E of 150W.

The 18z surface analysis indicated strong high pressure centered
near 40N138W with ridge extending northeast to Vancouver Island,
with low pressure inland over northern California. An ascat pass
from 1802z indicated gales persisting over the far southeast
Oregon offshore waters and the far northeast portion of the
northern California waters. These gales extended east into the
adjacent coastal waters.

The 12z models were all in very good agreement during the entire
forecast period. The high pressure ridge will slowly weaken and
shift southwest later tonight into Tuesday as a weak cold front
approaches the Washington and Oregon waters Tuesday. Meanwhile,
low pressure near the northern California coast will also weaken
through Tuesday night. This will allow winds to decrease below
gale by early Monday over the northern California and far
southern Oregon waters. For the evening forecast issuance, plan
on maintaining gales for PZZ815 and PZZ820 through about 06z with
winds dropping below gale later tonight over the offshore waters
while continuing over the coastal waters through late tonight.
The weak cold front mentioned above will move across the
Washington and Oregon waters Tuesday night through Wednesday
before dissipating over the central California waters Thursday.
The models also indicate the coastal trough slowly strengthening
again Wednesday night through Friday night. This will result in
gales again over the northern California/southern Oregon coastal
waters late Thursday night into Friday night. At this time, it
appears winds will remain just below gale over the offshore
waters. Will populate wind grids using the 12z GFS 10m winds
through the period.

.SEAS...The 18z sea state analysis indicated seas were mostly
within a foot of the latest WaveWatch III and ECMWF WAM, although
based on a recent altimeter pass the seas over the far east
portion of the northern California offshore waters were about 2
to 3 feet too low. Went with a 16 ft max for the analysis. For
the wave grids, will use the WaveWatch III, however will add a
few feet tonight over the northern California waters.



.PZ5 Washington/Oregon Waters...
.PZZ815...Inner Waters from Florence OR to Point St. George...
     Gale today into tonight.

.PZ6 California Waters...
.PZZ820...Inner Waters from Point St. George to Point Arena...
     Gale today into tonight.


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