marine weather discussion for N Pacific Ocean NWS ocean prediction center Washington DC 646 am PDT Mon Aug 21 2017
.Forecast discussion...Major features/winds/seas/significant .Weather for the North Pacific N of 30n and E of 150w.
The 12z surface analysis indicated high pressure centered near 38n138w with ridge extending northeast to southwest British Columbia. Trough extended north along the Oregon/Washington coast. The 06z GFS and NAM indicated few if any changes from the 00z run. The coastal trough will gradually strengthen again later in the week with gales again possible over the far southern Oregon and northern California coastal waters Friday night. At this time it looks like any gales will remain just east of the offshore waters so will cap winds at 30 kt. The 12z sea state analysis indicated that observed seas matched up well with the wavewatch iii forecast values.
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Gale warnings will be discontinued over the central waters through because the current pressure gradient has become relaxed as high pressure to the west continue to weaken while slowly retreating southwest and inland low pressure will also continue to weaken. Synoptic systems that will impact the waters will remain weak through most of the period keeping a relaxed pressure gradient across the waters. Satellite images continue to show clouds moving in anticyclonic circulation over the north waters but are moving in cyclonic direction over the central and southern waters. Lightning density map does not show lightning associated with the clouds over the region and even the sref model has prob 0 for tstms threat but inland over California. Latest observations show winds in gale force range over the eastern portion of the central waters. Otherwise winds are mainly from the north to northwest 5 to 20 kt over the north and southern waters. NCEP weather map at 06z has high pressure 1028 mb center near 40n140w with its northeast ridge extending into the north waters while inland trough extends northwest from low pressure over Southern California. Pressure gradient is tight over the central waters. Low pressure in the Gulf of Alaska has a cold front that stretches southwest passing west of the high pressure.
Models GFS/CMC/ecmwfhr/ukmethr/NAM have initialized fairly well the 06z synoptic observations with just minor differences on the central pressure value within 1 mb of the high pressure. Differences are similar in the extended period as high pressure retreats to the southwest. Otherwise, models are in fairly good agreement on the general synoptic pattern and wind speed. Will continue to use GFS as our main model guidance. In the short term the high pressure will slowly move southwest as it weakens. In the extended period, the high pressure will finally dissipate and another high pressure over central Pacific will move east and extend its ridge into the north waters. Inland trough will weaken in the short term but will start to strengthen in the extended period.
.Seas...Seas still range between 6 and 12 ft over the central waters with a peak at 14 ft while they range between 3 and 6 ft over the north and far south waters. Nww3 and ecmwfwave models fit well the observed seas pattern and have been quite consistent in the previous runs. Both wave models are in good agreement through most of the forecast period and so will not deviate from the previous model choice. Will stay close to nww3. In the short term, seas will remain higher over the central waters but will subside to less than 8 ft in the extended period.
.Extratropical storm surge guidance...
.Pz5 Washington/Oregon waters... None.
.Pz6 California waters... None.
.Forecaster kosier/musonda. Ocean prediction center.