marine weather discussion for N Pacific Ocean NWS ocean prediction center Washington DC 833 PM PDT Wed may 22 2019
.Forecast discussion...Major features/winds/seas/significant .Weather for the North Pacific N of 30n and E of 150w.
The GFS is initialized well against the available observations, earlier ascat passes and the 00z NCEP surface analysis. The GFS has good support from the non-NCEP models from 12z cycle. Since the current forecast is based on the 12z GFS and the more recent 18z GFS shows little change as the overall pattern has become more stable, no changes are planned for the evening update. Still expecting gales in the colder and unstable conditions over the next 18 to 24 hours, with gales maxing out in strength and extent tonight and early Thu with a decreasing trend setting in Thu as the high to the W recedes W. To the N there is a good model signal for NW gales developing over the at least the northernmost zones of pz5 Thu night into Fri night and maxing out Fri night as a new high develops and moves toward the northern waters while a coastal trough develops. Confidence in both areas of gales is above average. The 00z sea state analysis indicated that both the enp and ECMWF wam were slightly low versus the analysis, by up to 2 ft off California. Chose to update the wave grids through Fri night for the duration of the gale event except with a boost of up to 10 percent which matches up best with the current conditions and analysis, and also do not plan on making any changes to wave grids beyond Fri night. ----------------------------------------------------------------- Previous discussion...
Inland low pressure will persist while high pressure will remain strong to the west of the waters and that will in turn maintain a tight pressure gradient with winds in the Gale Warning threshold especially over the inner central and northern waters. Latest NCEP weather map now has high pressure 1032 mb near 40n137w that extends a ridge north into the Gulf of Alaska while inland low pressure 1000 mb over southern Nevada and Arizona border area extends a trough northwest into north California. Pressure gradient is fairly tight over the forecast waters and in particular the central waters. Maximum winds are northwest 35 kt over the central California waters.
At 500 mb level, models show a strong ridge along 140w that stretches into the Gulf of Alaska while a broad trough with some energy is depicted inland just east of the forecast waters. Models show that in the short term, the north portion of the ridge will shift east but will remain intact over the southern portion. Low pressure trough will recede into the central waters and that will induce more energy into the central waters forcing the surface trough to strengthen an force a tight pressure gradient over the central waters. In the extended period the ridge will keep swinging clockwise as more energy shifts into the southern waters. The ridge will strengthen again and push the energy over the southern waters inland but allow some energy to be introduced over the northern waters.
Global models GFS/CMC/ukmethr/ecmwfhr have initialized well the current synoptic observations with small differences up to 5 kt on the windspeed over the central waters. CMC is the strongest while ukmethr and ecmwfhr are weaker than the observations while GFS matches the observations. However, global models have a general agreement in the short term on keeping a tight pressure gradient over the eastern portions of the central and southern waters. Models also agree on weakening gradient into the extended period. For this issuance will continue to use GFS.
.Seas...They are largest over the central waters with a peak at 18 ft near Point Arena and Point Reyes. Otherwise seas range between 9 and 17 ft with relatively smaller seas over the far northern and far southern waters. Nww3 fits fairly well the sea state analysis of the observed seas. Ecmwfwave model is also close to the observed seas and in the short term, both wave models have shown a good agreement on keeping relatively large seas over the southern and central waters. Seas will build to peak over the northern waters in the extended period. Will keep consistency and stay with enp for seas.
.Extratropical storm surge guidance...There are no significant positive surge events expected over the next few days. However, please consult products issued by your local National Weather Service forecast office for additional information.
.Pz5 Washington/Oregon waters... .pzz800...inner waters from Cape Flattery to Cape Shoalwater... gale Thursday night into Friday. Gale possible Friday night. .Pzz900...Outer waters from Cape Flattery to Cape Shoalwater... gale Friday. Gale possible Friday night.
.Pz6 California waters... .pzz820...inner waters from point St. George to Point Arena... gale tonight into Thursday. .Pzz825...Inner waters from Point Arena to Pigeon Point... gale tonight into Thursday. .Pzz925...Outer waters from Point Arena to Pigeon Point... gale Thursday. .Pzz830...Inner waters from Pigeon Point to Point Piedras Blancas... gale tonight into Thursday.
.Forecaster Bancroft/musonda. Ocean prediction center.