Kelvin wave expected to raise West Coast sea levels through winter

A Kelvin wave moving north along the West Coast is expected to increase sea levels by six inches to a foot, traveling at roughly six miles per hour and reaching Oregon and Washington within a week. The surge will persist from October through February, according to oceanographers.

"It's not that this Kelvin wave is going to come and flood anything on its own," said Michael Jacox, a research oceanographer with NOAA's Fisheries Ecosystem Science Division. "If you start with sea levels that are 6 inches higher than normal, when you have really high tides, big storms or storm surges, the water levels are now 6 inches higher. The effects can be amplified."

Kelvin waves are a regular feature of El Niño events, forming when equatorial trade winds weaken or reverse, pushing a bulge of warm water eastward before it travels north and south along the Americas' coasts. The wave is a broad, shallow uplift—about 12 to 20 miles offshore and 200 meters deep—rather than a visible surface disturbance.

Scientists warn that the elevated baseline could worsen existing coastal challenges, such as beach erosion and flood risk. Sean Vitousek, a USGS research oceanographer, noted that past strong El Niño episodes produced the worst recorded erosion on the West Coast, and higher sea levels can increase wave impact on property and infrastructure.

Local officials are taking precautionary steps. Alyssa Napuri, deputy chief of staff for Orange County Supervisor Katrina Foley, said emergency sand is being placed on beaches as forecasts show water levels could rise six to 12 inches. Governor Gavin Newsom has declared a state of emergency to accelerate protective measures, while Washington state officials are monitoring the situation but have not yet initiated special preparations.

The ultimate impact will depend on the interaction of the Kelvin wave with storms and spring tides later this winter.