Kelvin Waves Raise West Coast Sea Levels as El Niño Strengthens

Rising ocean levels along the U.S. West Coast are signaling the arrival of a major development associated with the strong El Niño forecast for 2026. Kelvin waves, enormous ocean waves that travel beneath the surface, have raised sea levels by about 6 to 8 inches along parts of the California coast, increasing the potential for coastal flooding and bringing warmer water that can disrupt marine ecosystems.

Scientists expect several more Kelvin waves to reach the West Coast during the fall and early winter. Dillon Amaya, an assistant professor of atmospheric sciences at North Carolina State University, predicts the next wave will reach San Diego in late October or early November. The National Oceanic and Atmospheric Administration predicts that El Niño will remain strong through early 2027.

The phenomenon has attracted renewed public attention through explanatory videos on TikTok and X, although scientists have studied Kelvin waves for decades. Mark Cane, who developed one of the first models for forecasting El Niño and is professor emeritus of earth and climate sciences at Columbia University, expressed surprise at the sudden interest.

"It does surprise me – I mean, here it's been around all this time," said Mark Cane.

Cane added that the phenomenon was named after British physicist Lord Kelvin, who first described the waves in the late 1800s.

"I'm sure Lord Kelvin is happy in his grave."

Kelvin waves can form along the equator during El Niño years, when a vast region of the Pacific Ocean becomes warmer than usual. The resulting wave can extend thousands of miles, moving eastward beneath the ocean surface toward South America before splitting and traveling north along the West Coast and south toward Chile.

Cane compared the ocean movement to water sloshing inside a bathtub, while emphasizing the wave's unusual direction of travel.

"It's like an enormous bathtub sloshing around," said Cane.

The waves differ from the large surface waves generated by major storms and hurricanes. Their movement is primarily an ocean-scale process that gradually changes sea levels rather than producing a sudden wall of water.

"But the slosh is very peculiar, because it only goes west to east along the equator in a Kelvin wave."

Amaya said the waves should not be confused with tsunamis or surfable waves because their effects occur across enormous distances and develop gradually.

"It's not a wall of water, it's not a tsunami, it's not a wave you can surf," said Dillon Amaya.

He emphasized the planetary scale of the phenomenon and its influence on coastal ocean conditions.

"It's a planetary-scale wave."

Kelvin waves do not directly cause flooding, Amaya explained. Instead, the elevated sea levels they produce make coastal communities more vulnerable when storms or unusually high tides occur.

Josh Willis, a climate scientist at NASA's Jet Propulsion Laboratory, described the potential combination of El Niño, high tides and storm surge as a particularly dangerous scenario for California's coastline.

"El Nino, the high tide and the storm surge all coming at once."

Willis characterized the combination as a "triple whammy" for coastal communities. The risk became apparent in early October, when Tropical Storm Rachel brought storm surge to parts of Southern California that were already experiencing elevated sea levels.

According to Amaya, the Kelvin wave had raised sea levels by approximately 6 to 8 inches before the storm arrived. The subsequent surge flooded neighborhoods and left some oceanfront homes partially submerged.

Amaya said the elevated ocean levels likely intensified the storm's effects on affected communities.

"That storm surge was almost certainly made more devastating because of the Kelvin wave," said Amaya.

Warmer ocean water associated with Kelvin waves can also threaten marine ecosystems by reducing the availability of cold, nutrient-rich water that supports marine life. Researchers have observed tropical species in locations where they are not normally found.

Amaya cited unusual marine sightings as evidence of changing coastal conditions.

"We've seen tropical fishes in places that we don't normally see them," said Amaya.

One example was a whale shark spotted off San Diego, according to Amaya. Scientists have also observed evidence of seabird deaths in response to warmer coastal water temperatures.

"Like a whale shark was spotted off the coast of San Diego."

Strong El Niño years typically produce five to six Kelvin waves, according to Amaya. The waves generally diminish before El Niño reaches its peak, which typically occurs late in the year or in early January.

With NOAA researchers expecting strong El Niño conditions to persist into early 2027, additional Kelvin waves could continue to influence West Coast sea levels, coastal flood exposure and marine temperatures through the fall and early winter.