Marine Weather for HS 102

Forecast

marine weather discussion for N Pacific Ocean NWS ocean prediction center Washington DC 701 am PST Thu Nov 23 2017

.Forecast discussion...Major features/winds/seas/significant .Weather for the North Pacific N of 30n and E of 150w.

Ascat overpasses just after 06z returned several gale force wind retrievals associated with low pressure just NW of the outer Washington offshore waters. Model trends suggest the low begins to fill only after about 18z today as the low moves E skirting the northern opc zones. Accordingly, plan on adding in a brief period of gales until 18z as the associated low pressure trough moves across zone 900, with conditions dropping below warning criteria as the boundary weakens into zone 800 by 21z.

Upper ridge begins to shift east by Saturday, as upper trough digs southeast from the Gulf of Alaska. Digging shortwave carves out a high amplitude, slowly eastward progressing trough over the E Pacific late Saturday through Monday. A series of shortwaves are expected to round the base of the reloading trough and impact the offshore zones during this time. Model agreement and even run to run consistency Saturday and beyond remains poor at best, but not too unusual during a transition season. Accordingly, overall forecast confidence is below average.

For now will continue with previous grids from the night shift, which after Saturday, are based on a non-NCEP UKMET and ECMWF solution. Will re-evaluate entirety of forecast with upcoming 12z model suite.

----------------------------------------------------------------- Previous discussion...

Gale force winds slated for Saturday will be retained because a series of troughs and fronts will pass east across the northern waters. Satellite images show most of the cold cloud across the northern and central waters. At 06z, NCEP map has a cold front across the northern waters that extends from low pressure 992 mb over Vancouver Island and a trough trough extends southwest from the same low. High pressure 1022 mb over the southern waters has extended its ridge into the southeaster portion of the central waters and southern waters. Pressure gradient over the central and southern waters is fairly relaxed while over the northern waters, pressure gradient is fairly tight where maximum winds now just below gale force threshold have been observed. Though winds are now diminishing as a trough moves across the northern waters it will be quickly followed by a cols front that will re-enforce the gradient and allow winds to reach gale force strength again. Models GFS/CMC/ecmwfhr/ukmethr/NAM/NOGAPS/jma have initialized the 06z surface observations fairly well with just small variations mostly on the actual position of the cold front and trough to the west of the region. The models are generally in good agreement in the short term on building high pressure over the southern waters and as low pressure approaches the waters form the Gulf of Alaska, models agree on tightening the pressure gradient again over the northern waters and allow winds to increase. In the extended period, models show some differences on the position of low pressure that will approach from the southwest with GFS being the fastest and ukmethr being the slowest keeping ecmwfhr and CMC in between. GFS brings the low into the northern waters while ukmethr and ecmwfhr keeps it over the western edge of the northern waters while CMC weakens it and keeps it west of the northern waters. Otherwise, models have a very similar solution apart from timing and track differences. Ecmwfhr is the only model that keeps the winds below gale force. So either model choice will need some adjustments in the extended period. For now will retain the official winds.

.Seas...Peaked at 18 ft over the northeastern portion of the northern waters and they are relatively high over the rest of the northern and central waters. Seas are less than 6 ft over the southern waters south of 35n. Both wave models nww3 and ecmwfwave fit the observed seas pattern well but have differences on the actual peak value over the northern waters where nww3 has a peak at 18 ft while ecmwfwave peak value is 16 ft. For this issuance will continue with nww3 initially then switch to ecmwfwave in the extended period.

.Extratropical storm surge guidance...

.warnings...preliminary.

.Pz5 Washington/Oregon waters... .pzz800...inner waters from Cape Flattery to Cape Shoalwater... gale possible Saturday night into Sunday night. .Pzz900...Outer waters from Cape Flattery to Cape Shoalwater... gale today. Gale possible Saturday night into Monday. .Pzz805...Inner waters from Cape Shoalwater to Cape Lookout... gale possible Saturday into Saturday night. Gale possible Sunday night into Monday. .Pzz905...Outer waters from Cape Shoalwater to Cape Lookout... gale possible Saturday into Monday. .Pzz810...Inner waters from Cape Lookout to Florence or... gale possible Saturday into Sunday. .Pzz910...Outer waters from Cape Lookout to Florence or... gale possible Saturday into Sunday. .Pzz815...Inner waters from Florence or to point St. George... gale possible Saturday into Sunday night. .Pzz915...Outer waters from Florence or to point St. George... gale possible Saturday into Sunday night.

.Pz6 California waters... .pzz820...inner waters from point St. George to Point Arena... gale possible Saturday night. Gale possible Sunday night. .Pzz920...Outer waters from point St. George to Point Arena... gale possible Saturday into Sunday night. .Pzz925...Outer waters from Point Arena to Pigeon Point... gale possible Saturday. Gale possible Sunday.

$$

.Forecaster Collins/musonda. Ocean prediction center.

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