One of the first major signs of this year’s strong El Niño pattern has reached the United States in the form of a Kelvin wave, a deep ocean phenomenon currently raising sea levels along the West Coast. While oceanographers and climate scientists have long understood these subsurface waves, the current event has gained widespread public attention, with digital video explanations generating thousands of views across platforms like TikTok and X.
Named after the 19th-century British physicist Lord Kelvin—who also developed the Kelvin temperature scale and first described the wave mechanics in the late 1800s—the phenomenon develops during El Niño years when a vast expanse of the Pacific Ocean becomes significantly warmer than usual. Mark Cane, professor emeritus of earth and climate sciences at Columbia University and creator of one of the first predictive El Niño models, compares the mechanics to a planetary-scale container of water.
“It’s like an enormous bathtub sloshing around,” Cane says. “But the slosh is very peculiar, because it only goes west to east along the equator in a Kelvin wave.” Part of this warm water stretches thousands of miles, moving slowly east beneath the ocean surface until it reaches South America, where it splits and travels both north along the West Coast and as far south as Chile.
Despite their immense scale, these phenomena bear no resemblance to the massive, highly visible waves that crash into shorelines during hurricanes or major storms. Dillon J. Amaya, an assistant professor of atmospheric sciences at North Carolina State University, emphasizes that the disturbance is not a wall of water, a tsunami, or something that can be surfed. Instead, it is a planetary-scale wave whose impacts unfold gradually, raising baseline sea levels and bringing elevated risks of coastal flooding and warmer water temperatures.
While Kelvin waves do not cause flooding on their own, Amaya explains that they effectively load the dice by making background conditions significantly more favorable for inundation. When combined with triggering factors such as very high tides or major storms, the danger intensifies. Josh Willis, a climate scientist at NASA’s Jet Propulsion Laboratory, notes that the conditions raise the probability of a compound hazard along the California coast involving El Niño, high tides, and storm surges arriving simultaneously.
Southern California communities experienced this exact scenario in early October, when sea levels were already elevated by approximately six to eight inches due to the Kelvin wave. When Tropical Storm Rachel subsequently struck, the resulting storm surge flooded neighborhoods and left oceanfront homes partially submerged. Amaya points out that the storm surge was almost certainly made more devastating because of the pre-existing Kelvin wave.
In addition to altering sea levels, the waves transport warmer water up the coast, causing disruptions and placing environmental stress on marine life. Researchers have already documented tropical fish appearing in unusual northern locations, including a whale shark spotted off the coast of San Diego. The subsurface movement can also suppress nutrient-dense cold waters that sustain productive marine ecosystems, with researchers already observing instances of seabird mortality linked to the elevated coastal temperatures.
During a strong El Niño cycle, typically five to six Kelvin waves occur. Amaya predicts that the next wave will reach San Diego in late October or early November, with several additional waves anticipated through the fall and early winter before subsiding ahead of the El Niño’s peak. National Oceanic and Atmospheric Administration researchers project that the current El Niño pattern will remain strong through early 2027.
