Marine Weather for HS 102


marine weather discussion for N Pacific Ocean NWS ocean prediction center Washington DC 803 PM PDT Sat Mar 24 2018

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

The ascat pass from 19z shows winds to 30 kt associated with low center crossing the Oregon waters. The low will continue to weaken as it tracks se to a position near the SW Oregon coast by Sunday morning. The most recent enp guidance agrees well with current observations and wave grids. At this time I don't expect to make any changes to the grids or associated text forecast. As the trough strengthens along the California coast over the next several days a slight chance of gales remain along the northern and central California coast Monday night and Tue.

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Weakening low pressure over the Oregon offshore waters this afternoon will reach the Oregon coastal waters by tonight and then dissipate early sun. Unfortunately the latest ascat overpasses missed most of the offshore waters, but did indicate gales just off the southern Oregon coast at 1734z. Otherwise, we still expect a cold front to sweep E over Washington, Oregon and northern California offshore waters sun into Sun night. A warm front will lift NE and pass N of the offshore waters Mon into Mon night as high pressure builds to the W of the central and northern California waters. The high will persist W of these waters Tue. A coastal low pressure trough will form over Southern California sun, expand N to the central California coast Sun night and Mon, and the northern California coast Mon through Tue. Any gales associated with the Oregon low will quickly diminish this evening as the low continues to weaken as it moves se. There will be a threat for gales developing over the far eastern portions of the California offshore waters, or far inner zones, beginning later sun off the Southern California coast, then spreading northward Mon into Tue. For now, we will keep maximum winds near 30 kt and continue to monitor future model guidance as the threat for gales appears highest over the California coastal waters later sun through Tue. For the afternoon package we will rely on the previous grids into tonight, and then with excellent model agreement later tonight through Tue remain close to the 12z GFS winds (using the 10 meter winds over stable waters and higher first sigma layer winds over unstable areas), with slightly above average confidence in the forecast over the next few days.

For Tue night we will again remain close to the 12z GFS winds, with the California coastal trough lifting N to the SW Oregon coastal waters. For Wed through Thu night, we will transition our forecast and grids more toward the 12z ECMWF guidance as it appears to better match a general model consensus over the eastern Pacific during mid and later parts of next week, with the 12z GFS more of an outlier in bringing low pressure E toward the Queen Charlotte islands by Thu with the majority of the guidance keeping low pressure further W over the central Gulf of Alaska. This scenario is also closer to the wpc medium range forecast for mid and later parts of next week. We will use the ECMWF wind boost smart tool (which raises winds up to 15 percent) when transitioning toward the ECMWF winds Wed through Thu night over the region, as ECMWF winds typically verify too low. No warning headlines appear likely over the offshore waters Tue night through Thu night, with gales, if any, likely holding over the coastal waters during mid to late week due to the interaction between high pressure W of the waters and the coastal low pressure trough. Confidence levels are near average over the waters during mid to late week.

Seas...both the 12z enp wavewatch and ECMWF wam models appear to have initialized within a couple feet of the observations over the waters this afternoon. For the late afternoon package we will use a 50/50 blend of these two wave models into Tue night, and then as we transition toward the ECMWF for winds also transition toward the wam for sea heights for Wed through Thu night.

.Extratropical storm surge guidance...N/A


.Pz5 Washington/Oregon waters... None.

.Pz6 California waters... None.


.Forecaster Shaw/Mills. Ocean prediction center.

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