Marine Weather for HS 102


marine weather discussion for N Pacific Ocean NWS ocean prediction center Washington DC 619 PM PST Fri Feb 22 2019

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

Low pressure currently northwest of Vancouver Island will move slowly southeast tonight through Saturday night while weakening. Meanwhile, low pressure is expected to move into the southern pz5 waters by Sunday night. Gales are possible with this system across the offshore waters, but for now will keep the highest winds at 30 knots and see what the later model guidance shows. This low will then move inland Monday. Another low will then move across the northern pz6 waters by Tuesday with winds as high as 30 knots. Farther south, mainly light winds are expected across the southern pz6 waters tonight into Wednesday. For wind grids will continue to use the current grids throughout the forecast period. Current forecast looks reasonable and will continue to carry no warnings across the offshore waters during the forecast period.

For wave height grids will also continue to use the current grids throughout the forecast period.

Extratropical storm surge guidance...N/A.

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

The ascat wind retrievals from 17z and 18z overpasses this afternoon show a large area of 20 kt across the offshore waters with a few small areas of 25 kt along the California coast near Point Arena and Point Conception as a coastal low pressure trough interacts with high pressure to the W of pz5. This is down from last night where the pressure gradient had been tighter, and the 12z GFS/ECMWF both indicate that trend will continue as the high slowly builds E over the offshore waters. Further N, the ascat indicates a large area of 25 kt in the inner pz5 waters near a cold front currently over the area. The 12z models agree on this feature as well, with the GFS/ECMWF indicating the front will move inland allowing the winds to weaken overnight. The 12z ECMWF seems representative when compared with the rest of the 12z guidance over the next 24 hours, and is similar to the previous wind grids. As a result, am planning on starting out with a 75/25 blend of the 12z ECMWF and previous winds.

On sun, the 12z models indicate a shortwave trough will undercut the ridge in the E Pacific and move into the offshore waters by Sun night. The GFS has been indicating stronger surface development of the associated low pressure center as it passes through the nrn pz6/srn pz5 waters late sun into Sun night, as the ECMWF/UKMET have been weaker in the offshore zones. However, the forcing does seem all that impressive, and the 12z ECMWF and UKMET maintain Max winds at 30 kt in the offshore waters, so confidence with winds reaching gale force in the offshore waters is just below average at this point. However, with the channeling expected to develop between the low and the coast, winds should be higher in the coastal zones and confidence with gales developing there is above average. As far as the offshore winds are concerned, the 12z ECMWF again seems representative of the 12z guidance, so planning on continuing the blend used with the first 24 hours of the forecast.

The 12z models then diverge on the next system Tue into Wed, resulting from the differences of where an upper low cuts off as another shortwave phases into the trough across the nrn zones. The GFS has been very inconsistent, and the 12z run has become a fast outlier with taking the low inland. The 12z ECMWF/UKMET/Gem all keep the low offshore, and this idea is supported by a relatively strong signal in the 12z gefs members. Wpc medium range guidance is also favoring a solution closer to the 12z ECMWF, so planning on continuing the previous blend through the remainder of the forecast period.

.Seas...The 12z ECMWF wam is initialized slightly higher and better than the 12z wavewatch with the latest observational data, and indicates seas still up near 15 ft in the pz6 waters with the remaining cold advection over the area. The models agree somewhat over the short range, then start differing somewhat significantly on sun mainly as the result of the overdone GFS winds being higher than the ECMWF. Since the wind grids are a 75/25 blend of the 12z ECMWF winds with the previous grids, am planning on using a similar blend with the 12z ECMWF wam and the previous wave height grids.

.Extratropical storm surge guidance...N/A.


.Pz5 Washington/Oregon waters... None.

.Pz6 California waters... None.


.Forecaster nolt/Kells. Ocean prediction center.

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