The Washington outer coast is known for its rough seas and large waves. Extremes of wave height ranging from 50 ft (15m) to 90 ft (29 m) have been recorded on and beyond the continental shelf (Strickland and Chasan, 1989).

The height and direction of waves vary seasonally. During summer, waves are lower in height, predominately from the northwest. This results in longshore currents and sediment transport to the south. In winter, waves are generally higher and from the southwest, causing north-flowing currents and sediment transportation along the coast (Ballard, 1964 in Terich and Levenseller, 1986). The most severe wave conditions are caused by winter storms originating near Japan that move onto the U.S. Pacific coast. Storm winds ahead of warm fronts generate waves with wave heights up to 19-23 ft (6-7m); winds associated with cold fronts generate waves of 26-33 ft (8-10m) (Kachel and Smith, in press). Tsunamis, long-period sea waves produced by submarine earthquakes or volcanoes, occasionally strike the Washington coast. The Alaskan earthquake of 1964 produced a tsunami that reached a height of almost 13 ft (4m) at Seaview, Washington.

The oceanic current system off the coast of Washington is comprised of the California Current, Davidson Current, and California Undercurrent. The California Current flows southward beyond the continental shelf throughout the year. This current is approximately 1,000 km wide with a typical velocity of 10 cm/second. It brings water low in temperature and salinity, with high oxygen and phosphate contents (Hickey, in press). The California Current is strongest in July and August in association with westerly to northwesterly winds. The California Undercurrent, a narrow (20 km) subsurface countercurrent, flows northward along the upper continental slope with its core at a depth of about 200m. This current is also strongest in the summer with a mean velocity of about 10 cm/second. It brings warmer water with more saline, and less oxygen and phosphate (Hickey, 1979). An additional southward flowing bottom current (the Washington Undercurrent) flows deeper along the slope at about 400m depth during the winter. During winter, the California current either moves offshore or is replaced by the northward flowing Davidson Current. The Davidson Current flows during winter and early spring in association with southerly or southwesterly winds. It flows at a mean velocity of 20 cm/second and is associated with water masses with the same characteristics as the California Undercurrent. Currents over the continental shelf tend to follow the seasonal pattern of the oceanic currents, but are also strongly influenced by

- local winds
- bottom and shoreline configuration
- freshwater input
- From (Strickland and Chasan, 1989)

Simplified Mean Winter and Summer Current Patterns on the Washington Shelf:

- Mean Flow along the bottom is northward in all seasons
- Mean surface flow is southward in summer, accompanied by Coastal Upwelling of Deeper
- Near-bottom currents move northward and slightly offshore over the entire year
- Mean Surface Flow is northward in Winter, accompanied by Coastal Downwelling of Surface Water (Strickland and Chasan, 1989).

Local currents are highly variable and are dependent on passing weather systems, or large scale weather effects such as El Niño. While currents are flowing south along the coast during spring and summer months, the forces of northwesterly winds and the earth's rotation combine to push the surface waters offshore. As these waters move offshore they are replaced from below by cold and nutrient-rich waters. This process is called upwelling. It introduces nitrates, phosphates, and silicates that are essential for high plant based plankton (phytoplankton) production that forms the basis for the oceanic food chain. The majority of this upwelling occurs within 20-50 miles (10-20 km) off the coast. The strongest offshore flow occurs in the upper 33 ft (10m) of the water column. The submarine canyons that indent the Washington shelf are sites of increased upwelling (Parmenter and Bailey, 1985). Water upwelled from the Astoria and Quinault canyons moves across the shelf and is uplifted into the nearshore zone (Hickey, in press). Water upwelled in the Juan de Fuca canyon reaches almost to the surface layer and provides an increase in nutrients over the entire canyon (Freeland and Denman, 1982, in Hickey, in press).

Downwelling, or sinking of surface waters, occurs along the coast during winter when southwest winds push surface waters onshore. Tides on the Washington coast and Strait of Juan de Fuca occur with two high and low tides each day. A highest high and a lowest low tide are followed by a moderate high tide and a moderate low tide. Tidal changes along the coast are large, averaging about 12 ft (3.5m). This ensures a rich intertidal community.

The Columbia River is the largest river on the U.S. west coast. Its large input of freshwater to the ocean affects the coastal waters of Washington and Oregon. A low-salinity surface plume is directed northward along the Washington coast by the prevailing currents in winter.