marine weather discussion for N Pacific Ocean NWS ocean prediction center Washington DC 828 PM PDT Mon may 21 2018
.Forecast discussion...Major features/winds/seas/significant .Weather for the North Pacific N of 30n and E of 150w.
Made some near term changes in wind grids after comparing the 12z/18z GFS with the last ascat pass from 18z. Repopulated the grids overnight into Tue morning with the 18z GFS first sigma latyer winds as they are a closer match to the ascat data, but as the offshore ridge weakens later tonight and Tue the coastal enhancement of the northerly winds will diminish and by 18z Tue morning the existing grids using the GFS 10 meter winds will be representative of conditions.
Some minor differences noted in the latest model guidance in the track of the weak low to affect the pz6 waters in the extended time frame. Will leave grids as is for now as the 12z GFS has better support from the 12z ECMWF and global Gem versus the more northern track of the newer 18z GFS and wait until 00z models are in to make any changes.
Otherwise, no significant changes to the wind grids are expected at this time.
Seas...latest enp wave guidance in the pz6 near the central and northern California coast and adjacent offshore waters running up to 1 to 2 ft lower than current surface observations. 12z ECMWF wam seems to have a better handle with the seas in the area. Repopulated the wave grids with 100 percent 12z wam for the evening update overnight to 18z Tue but will transition back to existing grids after that as the ridge weakens along with pressure gradient with 12z GFS 10 meter winds and associated enp guidance looking more representative. Otherwise current wave grids look good, and do not expect any significant changes at this time. ----------------------------------------------------------------- Previous discussion...
12z global models in good agreement through most of the period. For the wind grids, will lean towards the 12z GFS through the period, which has good support from the 12z ECMWF.
High pressure to the northwest of the area will continue to interact with a coastal trough along California tonight, with winds to 25 kt possible over the pz6 waters. Ridge begins to weaken Tue into Tue night as a weakening cold front approaches the region. Models continue to show area of low pressure developing along the front west of the pz6 waters Wed and Wed night, and moving the low towards the pz6 waters on Thu. Models have been having a bit of a time with the track of this system over the past few days, but both the GFS and the ECMWF seem to be on the same Page with this system in taking a weakening low across the central pz6 waters Thu night and Fri, and then whatever is left of the system will move inland Fri night. GFS a bit stronger with the low with a few 25 kt winds in the southwest quadrant as it moves into the pz6 waters. Will keep winds to 20 kt for now as both the ECMWF and the UKMET are a bit weaker.
Models continue to show a weakening trend with the trough developing near Vancouver Island Wed night into Fri, with most of the global guidance keeping winds to 20 kt in the offshore waters, and up to 25 kt to the north of the offshore waters. See no reason to deviate from guidance on this system.
Coastal trough develops along California Fri night through Sat night, as a high pressure ridge builds to the W and NW. Models showing increasing northerly winds along the coast for Sat and Sat night, with some 30 kt possible. Will limit winds to 25 kt for now.
.Seas...Enp wave guidance still a bit off along the central and Southern California coast as ecmwfwave guidance seems to be a bit better in this area. For the wave grids, went with a 50/50 blend of the enp and ecmwfwave for tonight to try and bump enp seas up a bit. After tonight, lean towards enp guidance for the remainder of the forecast. Did limit seas to 10 ft over the California waters Sat night as going with slightly less wind over the area than the GFS is currently showing.
.Extratropical storm surge guidance...N/A.
.Pz5 Washington/Oregon waters... None.
.Pz6 California waters... None.
.Forecaster Bancroft/achorn. Ocean prediction center.