Kelvin wave may lift California coast by up to a foot as supercharged El Niño looms

A Kelvin wave moving eastward could lift California’s coastal sea level by as much as one foot as a powerful El Niño intensifies storm‑surge risk. The wave forms when the usual trade winds from South America to Asia weaken or reverse, allowing a massive slab of warm water to slosh eastward across the equator. It travels thousands of miles, carrying heat from the western Pacific toward the Americas. "You can follow them along … we see the higher sea levels along the equator, and when the wave reaches the coast of South America, it cannot continue to go eastward," Severine Fournier, a research scientist at NASA’s Jet Propulsion Laboratory, explained. "So it goes north and south." One such wave brushed the northern tip of South America in late August and is now racing toward the U.S. west coast, with models suggesting it could touch California within days and keep sea levels elevated for months while El Niño persists. Nate Mantua of NOAA’s Southwest Fisheries Science Center noted that a typical year holds a thick warm water layer in the western Pacific, but when winds slacken, that water surges back toward California. He added that Kelvin waves have been recorded for millennia and that sea levels have already risen about eight inches over the past century, so the wave adds on top of an existing rise. "We can predict a lot of the impacts, but not all," he said. This El Niño appears to be the strongest in at least a thousand years, already breaking temperature records months before its expected peak. The pattern also raises the chance of severe storms, flooding and coastal erosion, compounding the wave‑driven rise. Mike Jacox, a research oceanographer at the same NOAA center, warned that the wave is invisible and does not break like beach waves, but it will raise the baseline for high tides around Thanksgiving and Christmas, making storm surge more damaging. Governor Gavin Newsom declared a state of emergency, staging road‑closure and snow‑removal gear and readying the National Guard for rescue missions. The California Coastal Commission urged residents to inspect flood‑prone areas, improve drainage and address erosion before the storms hit. "A key observation from past El Niño events is that the most damaging storms are often those that coincide with the highest tides," wrote commission head Kate Huckelbridge. Past strong El Niños in 1983, 1998 and 2016 helped refine forecasts, but Mantua cautioned that the combination of rising sea levels and an exceptionally intense El Niño could cause damage beyond any previous winter.

Context

Kelvin waves are a natural part of the ocean’s response to wind changes, but when they align with a record‑breaking El Niño they can temporarily boost coastal water levels, increasing flood risk during already high tides.