marine weather discussion for N Pacific Ocean NWS ocean prediction center Washington DC 824 PM PDT sun Jul 21 2019
.Forecast discussion...Major features/winds/seas/significant .Weather for the North Pacific N of 30n and E of 150w.
Inland trough near northern California will continue to be weak and pressure gradient will also continue to be relaxed and winds remain below gale force threshold through most of the forecast period while high pressure will continue to the west of the forecast waters. Weak fronts will move east and will cross the northern waters. Latest NCEP weather map has broad high pressure that extends form the central Pacific into the central and southern waters. Low pressure 1015 mb juts near the tip of the northwest washing ton waters has a cold front stretching south over the western portions of the Washington and Oregon waters. Inland trough over the north California has weakened and pressure gradient has remained well relaxed over most of the forecast waters but still relatively tight over the north California waters.
Seas have continued to be relatively small with a peak now at only 8 ft over the central California waters. Seas range between 6 and 7 ft over the central California waters. Otherwise seas range between 4 and 6 ft over the rest of the forecast waters. Nww3 fits very well the seas observations and has continued to be fairly consistent with observations in previous runs. Ecmwfwave has also continued to be close to the observed seas pattern. In the short term, both wave models have a good agreement on allowing seas to remain small with relatively large seas over the central waters. Will continue using enp for the seas grids.
Global models at 500 mb depict a broad upper level ridge that extends north from central Pacific into the waters leaving only the Washington waters and area that is under an upper level trough with some energy that will allow surface low pressure to move east across the northern waters. Stability index pint to a fairly stable atmosphere across the waters and there is still absence of strong shear across the waters. This synoptic pattern will not vary much through most of the forecast period and so will keep winds below gale force warning and will continue with GFS for winds.
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The 18z surface analysis indicated low pressure just west of the northern Washington offshore waters, with cold front extending south and warm front east of low. The latest available ascat passes from 1705z and 1817z depicted the low very well, with the strongest winds to 20 kt in west semicircle of low, with winds 10 to 15 kt east of low. Another area of 20 kt winds was noted over the central California waters which match up well with model forecast fields. Winds were mostly 15 kt or less over remainder of area.
The 12z models continue to be in very good agreement during the forecast period with only minor differences noted. The cold front currently west of the Washington/Oregon and northern California waters will move into the waters tonight and Monday before dissipating Monday night as the low lifts north of area. Another weak front is forecast to move into the Washington and Oregon waters Wednesday night into Thursday before becoming stationary and dissipating Thursday night. Winds with both these fronts will be well below gale, and will continue to carry no warning headlines through the period. Meanwhile, the trough along the California coast and southern Oregon coast will slowly strengthen through the week. However, any gales will be confined to the far southern Oregon and northern California coastal waters Wednesday into Thursday.
.Seas...The 18z sea state analysis indicated that observed seas continue to match up well with the current wave grids which are based on the wavewatch. With this in mind, will continue to use the wavewatch through the period with differences between wavewatch and ECMWF wam negligible.
.Extratropical storm surge guidance...N/A.
.Pz5 Washington/Oregon waters... None.
.Pz6 California waters... None.
.Forecaster musonda/kosier. Ocean prediction center.