What are Kelvin waves, and what do they mean for El Niño?
A Kelvin wave can temporarily elevate coastal water levels. The current wave is forecast to reach California this fall.
A wave heading for California could lift sea levels by a foot, exaggerating coastal flooding and erosion that could cause serious damage.
In an El Niño year, another climate term is likely to make headlines: the Kelvin wave. These waves are not like the breaking waves at the beach, but are planetary waves that occur over long periods of time, stretching thousands of miles across the equatorial Pacific.
Kelvin waves are vast pulses that travel through the ocean or atmosphere. Forecasters monitor them because a warm, or downwelling, Kelvin wave can transport subsurface heat eastward and contribute to the development or strengthening of an El Niño event. However, a single Kelvin wave does not guarantee an El Niño.
What causes Kelvin waves?
Easterly trade winds normally push warm surface water toward the western Pacific. When those winds weaken or reverse and become a burst of westerly wind, warm water can begin sloshing east, initiating a downwelling Kelvin wave along the equator.
How long do Kelvin waves last?
A Kelvin wave generally takes about two to three months to cross the tropical Pacific. Its influence can persist as subsurface heat reaches the surface or the wave interacts with the coast of South America.
How do Kelvin waves warm the Pacific Ocean?
Sea level height data from the international Sentinel-6 Michael Freilich satellite collected from March to May 2026. (Image: NASA/JPL-Caltech)
Scientists have been closely monitoring sea level height data from satellites, including the international Sentinel-6 Michael Freilich satellite, showing the emergence of a Kelvin wave.
A downwelling Kelvin wave thickens the ocean’s warm upper layer and pushes the thermocline, the boundary between warm surface water and colder deep water, farther down. This limits the amount of cold water reaching the surface and can raise ocean temperatures.
Could Kelvin waves raise sea levels along the U.S. Pacific coast?
The incoming tide and swell approaches a recently built sand berm and closed parking lot at Aliso Beach in Laguna Beach, where recent storm surges caused damage to the parking lot and erosion, Tuesday, Sept. 1, 2026. (Allen J. Schaben / Los Angeles Times via Getty Images)
When an equatorial Kelvin wave reaches South America, some of its warm water can turn north and travel along the coast as a coastally trapped Kelvin wave. Because warmer water expands, the wave can temporarily elevate coastal water levels.
The current wave is forecast to reach California in late September and move toward San Francisco by early October, potentially raising water levels by roughly 1 foot. That temporary increase could worsen coastal flooding and erosion if it overlaps with high tides, large surf or a coastal storm. It would occur on top of the long-term sea level rise caused by climate change. NASA says past El Niño events have raised West Coast water levels by more than 7.9 inches.
What is the difference between Kelvin waves and Rossby waves?
Equatorial Kelvin waves travel east, while Rossby waves generally travel west and move more slowly. When a Kelvin wave reaches the eastern Pacific, part of its energy can reflect westward as a Rossby wave. Both are planetary-scale waves, not ordinary beach surf.
Can Kelvin waves influence hurricanes?
This aerial view shows a sinkhole on a street and driveway of a seaside home affected by large swells produced by Hurricane Marie in Malibu, California, on Sept. 8, 2026. Hurricane Marie stayed well offshore of Southern California during Labor Day weekend, but its large swells produced dangerous surf and rip currents, with waves reaching around 10 feet in some areas. (Photo by David Swanson / AFP via Getty Images)
Oceanic Kelvin waves do not directly create hurricanes. By influencing El Niño, however, they can help change tropical rainfall and wind shear. El Niño often suppresses Atlantic hurricane activity while favoring activity in parts of the Pacific. Atmospheric Kelvin waves can also organize thunderstorms and sometimes make conditions more favorable for tropical cyclone formation.
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