marine weather discussion for N Pacific Ocean NWS ocean prediction center Washington DC 819 PM PDT Thu Apr 25 2019
.Forecast discussion...Major features/winds/seas/significant .Weather for the North Pacific N of 30n and E of 150w.
Per the 00z NCEP surface analysis a high pressure ridge was located across the Washington, Oregon and California offshore waters. A trough of low pressure was located inland extending from S central Oregon, down through the central parts of California. Will populate the grids with a 66/33 blend of the existing grids and 00z warw through 26/21z to have a bit of new data in the forecast, then allow the rest of the grids and warning headlines to remain as is given the 18z GFS/NAM are in good agreement with the prior 12z guidance. Please see the previous discussion below for additional information.
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Current surface analysis shows a 1031 mb high centered to the W-NW of the outer Washington waters near 48n135w with a ridge axis extending S-se to W of the central California waters near 36n132w. A 1012 mb low is centered across inland northern California near 40n122w with surface troughing extending southward from the low center across the San Joaquin Valley. Latest ascat passes depict an area of 20 to 25 kt winds across the Oregon and Washington waters, and a potentially similar area, missed in the latest pass, off the coast of northern California.
The pressure gradient in place between the troughing across interior California and high pressure to the W of the offshores is expected to strengthen Friday night into Saturday over the southern Oregon and northern California waters. 12z model guidance continues with consistency in the placement of the strongest winds and timing of gale force winds beginning Friday night in the coastal zones and spreading outward into pzz820 by Saturday morning. The 12z ECMWF is slightly slower and the 12z GFS is slightly stronger, and so as a result, blended GFS and ECMWF solutions with slightly more weight given to the GFS, maintaining the timing aspect of onset of gales, but tapering down the wind field resulting in an area of 35 to 40 kt. Gale force conditions are expected through Sunday night. Winds will begin to gradually diminish Monday as both the high pressure to the NW shifts farther northward and the inland troughing persists across California but begins to slowly move eastward Monday night into Tuesday. Thereafter, high pressure located across the Gulf of Alaska will start building back south- southeastward early next week with 20 to 30 kt northerly winds expected off the northern California waters.
Seas...seas will begin building ahead of the onset of gale force conditions off the northern California coast Friday and guidance anticipates a peak wave height of 17 ft Sunday around 12z generally in the coastal and inner northern California waters. Otherwise, favored the 12z enp wave model for the grids given good confidence in the 12z GFS wind field through a majority of the forecast period.
.Extratropical storm surge guidance...N/A.
.Pz5 Washington/Oregon waters... .pzz815...inner waters from Florence or to point St. George... gale possible Sunday.
.Pz6 California waters... .pzz820...inner waters from point St. George to Point Arena... gale Saturday. Gale possible Saturday night into Sunday night.
.Forecaster Holley/Huffman. Ocean prediction center.