A Kelvin wave carrying unusually warm water toward the Americas is raising sea levels along California's coastline, and researchers say it could worsen storms and flooding in a state already preparing for a severe El Niño. The wave is a common ocean phenomenon linked to El Niño, but this one is expected to be more powerful than usual. Richard Seager, a research professor at Columbia University's Lamont Doherty Earth Observatory, said the effects of such a wave are not visible to the casual observer.
Seager said a photograph in The New York Times that showed a surface wave hitting a beachfront condominium was misleading. The National Oceanic and Atmospheric Administration compares a Kelvin wave to water sloshing slowly in a bathtub, with levels rising and falling rather than crashing against the shore. The wave causes temporary sea level rise of roughly 6 to 12 inches. Normally, trade winds push warm water near South America westward toward Asia, pulling cooler water up along the equator and keeping the eastern Pacific cool.
During El Niño, those trade winds weaken, letting warm water piled up in the western Pacific flow back east as a Kelvin wave. The wave travels along the equator and reaches Peru and Ecuador before turning north toward British Columbia and south toward Chile. The current El Niño is a so-called super event expected to rank among the strongest on record. Eastern Pacific temperatures ran 5 degrees Celsius above normal on October 4, which Seager described as a very large anomaly.
Every inch of sea level rise increases the risk of flooding during storms and high tides, and El Niño can push the North Pacific storm track southward, bringing more storms into Southern California. California Gov. Gavin Newsom declared a state of emergency in September to prepare for a particularly severe El Niño season. Rising seas driven by climate change are already inundating seaside roads, railways and neighborhoods in the state.
Emily Yam, senior director of learning and public engagement at the Aquarium of the Pacific in Long Beach, California, said communities without infrastructure built to protect their coastlines will feel the effects, because 6 to 12 inches is not a trivial change. Warmer water also draws species such as hammerhead sharks and devil rays farther north than usual, and NOAA noted that a 151-pound striped marlin caught in August off Washington set a state record.
Hotter water puts stress on coastal ecosystems, and Yam said scientists are preparing for a possible die-off of California's kelp forests, which thrive around 50 to 60 degrees Fahrenheit but have recently seen water reach well into the 70s. The Kelvin wave is pushing warm water into an area already affected by a marine heatwave since May of last year. The temporary sea level rise is expected to last through the start of winter, and El Niño, which began in June, is forecast to weaken rapidly going into 2027.
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