Marine Weather for HS 102


marine weather discussion for N Pacific Ocean NWS ocean prediction center Washington DC 827 PM PDT Fri Jul 20 2018

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

Per the NCEP 00z a 1013 mb low was located over the eastern part of the central pz6 waters with a low pressure trough extending south from the low center. A high pressure ridge was located over the rest of the offshore waters.

The 18z GFS/NAM where in good agreement with the prior 12z model package. In the guidance has been in good agreement with each model cycle during the course of the week. With that noted felt it was reasonable to populate the grids with the latest GFS for this package, with some tweaks made to the grids to keep in the gales through Saturday over the northeast pz6 waters while also making sure to match up the boundary areas between the opc offshore areas and the adjacent WFO coastal areas. Gales winds still expected to subside over the northeast pz6 waters by early Saturday as the low pressure trough east of the region weakens, while a weak area of low pressure forms southwest of the waters. Additionally the high pressure ridge west of the waters retreats to the west which further decreases the pressure gradient overhead.

Repopulated the seas with the 18z nww3 given the choice to use the 18z GFS over the forecast period.

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

High pressure to the west of the northern waters combined with inland low pressure over northern California and that resulted in a tight pressure gradient over the eastern portion of the central waters. The gradient will relax in the extended period and winds will diminish to below gale force threshold. The goes16 rgb geocolor satellite images still show skies with warm clouds over the northern waters and cold clouds are still depicted over the southern waters. The latest NCEP weather map still has high pressure 1035 mb along 140w about 45n and it extends a ridge into the northern waters. Inland low pressure now 1011 mb over northern California extends a trough northwest into the central waters and the pressure gradient is quite tight over the central waters where maximum winds from the north are in the gale force range.

There is still some energy embedded in an inverted upper level trough over the central waters and in the short term, this energy will shift west as high pressure builds in over the land. The upper level high pressure will slowly build west over the waters in the extended period.

Global models GFS/CMC/ecmwfhr/ukmethr/NOGAPS have initialized well the latest surface observations with just small variations on the actual position and value of the high pressure to the west of the region. Models agree well in the short term keeping the high pressure to the west of the region while weakening inland low pressure and that will allow gradient to relax. Will use GFS for winds.

.Seas...They still peak at 15 ft over the area with maximum winds and they range between 6 and 12 ft over most of the region except the far southern waters where seas are less than 6 ft. Nww3 and ecmwfwave models fit well the observed seas pattern over the forecast waters including the high seas. The wave models agree in the short term on keeping relatively large seas over the central waters. Will just Sat with enp fore seas.

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


.Pz5 Washington/Oregon waters... None.

.Pz6 California waters... .pzz820...inner waters from point St. George to Point Arena... gale tonight into Saturday.


.Forecaster Holley/musonda. Ocean prediction center.

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