marine weather discussion for N Pacific Ocean NWS ocean prediction center Washington DC 302 PM PDT Mon Oct 16 2017
.Forecast discussion...Major features/winds/seas/significant .Weather for the North Pacific N of 30n and E of 150w.
A 1908z ascat-a overpass indicated winds running generally 20 to 25 kt in the SW flow ahead of a cold front approaching the NW waters, covering most of NW half of pz5 waters. These winds are close to 12z GFS 10m winds. Winds are light in the SW-NE ridge over the se pz5 waters while ascat indicated northerly winds to 20 kt in the gradient between a coastal trough and the weak ridge to the NW. The 1730z pass of ascat showed light winds elsewhere to the S with the trough. These features are weakening as the front approaches. Low pressure was centered near 53n 130w per the 18z NCEP preliminary surface analysis with an associated cold front extending southwest from the low center. Although no gales are apparent from ascat, another low will form just north of the Washington waters tonight in response to some digging of a shortwave trough coming from the W with an associated cold front pushing southeast over the Washington and Oregon offshore waters tonight into Tue, with the front dissipating over Oregon waters later Tue night. Weak high pressure will cross the waters north of the front late Tue and early Tue night. Most of the 12z model guidance including the GFS and ECMWF bring a period of gales to the NW Washington offshore waters near the front tonight, and we will also add gales to NW part of inner zone 800 for the afternoon package, for tonight. Visible GOES-W satellite omagery and GFS stability guidance suggest there could be negative static stability at times behind frontal passages. With good agreement between GFS and other model guidance in the near term will populate grids with the 12z GFS modified with the smart tool that places stronger first sigma level winds in unstable areas and 10m winds in stable areas. A stronger cold front will then push E and move over Washington, Oregon and northern California offshore waters later Tue night and Wed. This front will bring a good chance for gales over all of the Washington and the NW Oregon offshore waters late Tue night into Wed. The front will weaken as it moves into northern and central California waters Wed night into Thu with winds forecast to diminish below gale force, except over NW Washington waters where gales may re-develop as a strong upper level disturbance moves east into the area with associated negative static stability. For now plan to keep gales out of the two southern pz5 zones. Any gales will then end over the offshore waters during Thu as the disturbance slowly lifts north of the waters, and the front continues to slowly weaken as it moves further to the south. A weak high pressure ridge will then build into the region Fri ahead of the next cold front.
Starting Fri night the models start to diverge with the timing of the next frontal system to affect to waters Fri night with the GFS looking like a slow outlier while the 12z UKMET/ECMWF are faster and 12z Gem agood compromise. Since grids arev not available for the Gem plan to the use the more representative old 00z ECMWF for winds starting 18z Fri and for the reminder of the forecast, which is close to wpc guidance.
.Seas...Both the 12z enp wavewatch and 12z ECMWF wam appear to have initialized quite well over the offshore water per the latest observations and earlier altimeter data. Sea heights range from 5 feet over Southern California waters to around 10 to 12 ft in the far NW. For the new package we will use a 50/50 blend of the wavewatch and wam for tonight into Fri and after that with old ECMWF used for winds, will use the 00z ECMWF wam.
.Extratropical storm surge guidance...N/A.
.Pz5 Washington/Oregon waters... .pzz800...inner waters from Cape Flattery to Cape Shoalwater... gale tonight. Gale Wednesday. Gale possible Saturday into Saturday night. .Pzz900...Outer waters from Cape Flattery to Cape Shoalwater... gale tonight. Gale Tuesday night into Wednesday. Gale possible Wednesday night into Thursday. Gale possible Friday night into Saturday. .Pzz805...Inner waters from Cape Shoalwater to Cape Lookout... gale Wednesday. Gale possible Wednesday night. Gale possible Saturday into Saturday night. .Pzz905...Outer waters from Cape Shoalwater to Cape Lookout... gale Tuesday night into Wednesday. Gale possible Wednesday night. Gale possible Friday night into Saturday night. .Pzz810...Inner waters from Cape Lookout to Florence or... gale possible Wednesday night. Gale possible Saturday into Saturday night. .Pzz910...Outer waters from Cape Lookout to Florence or... gale Wednesday. Gale possible Wednesday night. Gale possible Friday night into Saturday night. .Pzz915...Outer waters from Florence or to point St. George... gale Wednesday. Gale possible Wednesday night into Thursday. Gale possible Saturday into Saturday night.
.Pz6 California waters... None.
.Forecaster Bancroft. Ocean prediction center.