A massive ocean wave racing across the Pacific could reach the US West Coast within days, raising the risk of coastal flooding and threatening homes and communities along the shoreline.
Dillon Amaya, an oceanographer at North Carolina State University, said several Kelvin waves are traveling north toward the coast. The next is forecast to arrive near San Diego between late October and the first week of November.
Another Kelvin wave reached California earlier this month and is thought to have worsened coastal flooding and contributed to evacuations of waterfront properties during Tropical Storm Rachel.
Kelvin waves are enormous pulses of warm seawater that develop when the tropical winds normally pushing water westward weaken during an El Niño event.
As those winds fade, warm water that usually gathers in the western Pacific surges eastward along the equator. It first strikes South America before traveling north along the coast toward the United States, temporarily lifting sea levels by as much as a foot.
The National Oceanic and Atmospheric Administration has warned that California could face a “quintuple whammy” this year. Warmer ocean temperatures, tropical storms, unusually high tides, Kelvin waves and climate change could combine to elevate sea levels and put thousands of coastal residents at risk.
“There are one or two more that are still in the tropics,” NOAA said in a statement issued October 6.
Amaya said strong El Niño years commonly produce five or six Kelvin waves as abnormally warm ocean temperatures disrupt weather patterns around the world.
A Kelvin wave in early October 2026 is believed to have intensified flooding linked to Tropical Storm Rachel
Oceanographer Dillon Amaya expects another Kelvin wave to reach the US in late October or early November
The most recent Kelvin wave to move up the West Coast is believed to have compounded Rachel’s effects, raising sea levels by several inches and allowing waves and storm surge to cause greater damage.
From October 10 to 11, 2026, the remnants of Tropical Storm Rachel inundated roads and homes on the Long Beach Peninsula and Newport Beach’s Balboa Peninsula.
In Long Beach, waves spilled over the shoreline and damaged the boardwalk before pushing seawater into houses. Residents were evacuated, and roughly a dozen homes were declared unsafe to occupy.
Other south-facing beaches in the San Diego region also experienced flooding, erosion and wave damage.
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“That storm surge was almost certainly made more devastating because of the Kelvin wave,” Amaya told NPR.
NOAA explained that Kelvin waves can raise sea levels by 6 to 12 inches. On their own, that temporary increase may pose limited danger, but the impact can become much more serious when it coincides with exceptionally high tides or storm surge.
Amaya described the phenomenon as a “planetary-scale wave” stretching thousands of miles. Kelvin waves initially hit the northern half of South America, then turn north and travel along the coasts of Mexico and the United States.
Mark Cane, a climate scientist and professor emeritus at Columbia University, likened the process to an “enormous bathtub” sloshing back and forth during El Niño years.
Several Southern California homes were evacuated after powerful waves hit the coast in October 2026
Kelvin waves develop during El Niño, first reaching South America before moving north along the coast toward the US
‘The slosh is very peculiar, because it only goes west to east along the equator in a Kelvin wave,’ Cane noted.
AccuWeather Long-Range Expert Paul Pastelok said the El Niño that emerged this summer could be a record-breaker, surpassing similar events in 1982 and 1997, with temperatures in the Pacific predicted to rise by nearly five degrees Fahrenheit.
In the US, this warming pushes the natural jet stream flowing over the center of the country farther south, bringing moisture and storms to many southern states that rarely see snow during winter.
In the Pacific, the warmer sea-surface temperatures create the perfect recipe for more tropical storms and hurricanes to form. At the same time, the normal east-to-west trade winds weaken or reverse.
Without those usual trade winds holding the warm water in the west, the giant Kelvin waves form and slowly carry the elevated warm water eastward across the Pacific and up the West Coast.
AccuWeather forecasters have warned that the potentially record-setting heat in the Pacific this year will likely carry the effects of El Niño well into 2027, possibly affecting the climate throughout the entire year.
The next Kelvin waves are expected to arrive along the West Coast throughout the fall and early winter, according to Amaya. Typically, the waves fade before the peak of an El Niño event in early January.
