marine weather discussion for N Pacific Ocean NWS ocean prediction center Washington DC 823 PM PDT Mon Aug 21 2017
.Forecast discussion...Major features/winds/seas/significant .Weather for the North Pacific N of 30n and E of 150w.
Synoptic systems affecting winds and seas over the forecast waters will remain weak and winds will remain below gale force threshold through the period. Satellite images show mostly cloudy skies across the forecast waters with cyclonic circulation over the south waters. Latest observations show higher winds to 25 kt over the central waters. At 00z the NCEP weather map has high pressure 1026 mb near 35n140w with its ridge extending northeast into the north waters. Low pressure 1014 mb centered over the western edge of the southern waters. Pressure gradient is fairly relaxed across the region and the models GFS/CMC/ecmwfhr/ukmethr support keeping a relaxed pressure gradient through most of the forecast period. The models have initialized well the 00z surface observations with just minor differences that do not change the main synoptic pattern. Will stay with GFS.
Seas are relatively higher over the southern waters with a peak at 9 ft. Seas range between 3 and 6 ft over the northern and far southeastern waters. Nww3 and ecmwfwave have both agreed well on subsiding seas to below 8 ft across the region most of the period.
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The 18z surface analysis indicated high pressure centered near 38n138w with ridge extending northeast into southern British Columbia. Weak low perssure was just northwest of the Southern California waters. The most recent ascat pass from 1740z missed most of the offshore waters, but did get a decent portion of the coastal waters indicated the strongest winds around 25 kt over the southern Oregon/northern California waters.
No big changes are anticipated for grids as the 12z models continue to be in very good agreement during the period. At the mid/upper levels, closed low off the Southern California coast will slowly shift east the next few days while weakening. At the surface, the high pressure ridge will weaken the next few days as a weak cold front approaches the Washington and Oregon offshore waters later Tuesday, then passes southeast across the waters Tuesday night and Wednesday. The front will then move into the northern California waters Wednesday night before dissipating over the central California waters Thursday. Winds with this front will remain well below gale levels. Otherwise, the coastal trough will reamain weak through midweek before strengthening again later Thursday through Friday night, then weakening again over the weekend. It appears now that any gales later in the week will be confined to the far southern Oregon and northern California coastal waters as all models indicate winds below gale over the adjacent offshore waters. Will continue to populate wind grids using the GFS 10m winds with very good support from ECMWF/UKMET/CMC.
.Seas...The 18z sea state analysis indicated that observed seas were within a foot of the model guidance. Will continue to use the wavewatch iii for wave grids through the period.
.Extratropical storm surge guidance...N/A.
.Pz5 Washington/Oregon waters... None.
.Pz6 California waters... None.
.Forecaster musonda/kosier. Ocean prediction center.