Concern mounts over slow-moving, planetary-scale Kelvin wave heading for Calif

A massive, slow-moving planetary Kelvin wave propelled by an exceptionally strong El Niño is heading toward the US West Coast and could raise California sea levels by as much as a foot for months. Kelvin waves form when the Pacific trade winds weaken or reverse during El Niño, allowing a huge slab of warm water to surge east along the equator and then divert north and south when it reaches the Americas. One such wave hit northern South America in late August and is moving up the coast; scientists expect its influence to linger through the winter and into early next year. Sea levels have already risen about eight inches over the past century, and the current El Niño - likely the biggest in at least 1,000 years with temperatures already exceeding previous records - supercharges the threat by trapping warm water along the coast.

The elevated baseline from the Kelvin wave raises the floor for high tides, storm surge and coastal erosion, increasing the risk that storms coinciding with peak tides this winter will cause major flooding and damage. California has declared a state of emergency, staged road‑closure and snow‑removal equipment, readied the National Guard and urged residents to shore up vulnerable areas and drainage. Past strong El Niño years (1983, 1998, 2016) guide expectations, but researchers warn the combination of higher sea levels and an unusually intense event could produce worse impacts than seen in previous major El Niño winters.