Kelvin Wave Lifts West Coast Sea Levels Up to a Foot as El Niño Intensifies

Sea levels along the U.S. West Coast have risen by about 6 inches to a foot since early October 2026 as a Kelvin wave — a pulse of warmer-than-normal ocean water — moves north from the tropics, according to an Associated Press report carried by PBS NewsHour. Researchers tie the event to this winter's strong El Niño, a periodic warming of the equatorial Pacific that typically raises sea levels and ocean temperatures far from the tropics.

What a Kelvin wave actually is

A Kelvin wave is not a breaking wave like a tsunami. Oceanographers describe it as a wide, low bulge of warm water, extending roughly 12 to 20 miles offshore and about 200 meters deep, that travels along the coastline rather than crashing onto it. The PBS/AP report compares the effect to water sloshing in a bathtub or swimming pool during an earthquake. The current pulse is moving north at an estimated 150 miles per day.

Michael Jacox, a research oceanographer with NOAA Fisheries' Ecosystem Science Division, and Sean Vitousek, a research oceanographer with the U.S. Geological Survey, are among the scientists cited in the PBS/AP report tracking the wave's progress up the coast.

Why this is tied to El Niño

Kelvin waves occur regularly during El Niño events, but researchers say this winter's strong El Niño could intensify their effects. The PBS/AP report notes that past major El Niño years — 1982-83, 1997-98 and 2015-16 — were associated with record beach erosion on the West Coast. Scientists tracking the current event expect this El Niño to generate roughly five to six Kelvin waves in total, with activity continuing from October 2026 through February 2027.

NASA's Jet Propulsion Laboratory, which leads the agency's sea level change science team, describes El Niño more broadly as a climate pattern marked by higher-than-normal sea levels and warmer ocean temperatures along the equatorial Pacific, driven in part by thermal expansion of warmer water. NASA scientist Ben Hamlington and University of Hawaii oceanographer Phil Thompson, both cited in a NASA/JPL analysis, have linked strong El Niño winters to a higher chance of coastal high-tide flooding on North and South American Pacific coasts.

King tides add another layer in the Bay Area

In the San Francisco Bay Area, the Kelvin wave's effect is compounding with seasonal king tides. CBS News' San Francisco affiliate reported that December 2026 tides are forecast to reach 7.33 feet, which the report's headline describes as the highest king tide in the Bay Area in 18 years, though still short of the all-time San Francisco record of 8 feet set on January 27, 1983.

According to the CBS SF report, several factors are converging this winter: Earth reaches its closest point to the sun in early January, the moon reaches perigee, and an 18.6-year lunar wobble cycle is currently in what the report calls its amplified phase. El Niño's warmer water adds further height through thermal expansion, on top of at least 8 inches of long-term sea level rise attributed to climate change over the past century.

What officials are watching

Local governments are monitoring the combined effects. The PBS/AP report cites Alyssa Napuri, deputy chief of staff for Orange County Supervisor Katrina Foley's office, among local officials following the wave's progress for potential coastal flooding and erosion impacts.

NASA's earlier sea level analysis, conducted with its JPL-led science team, projected that by the 2030s, high-tide flooding that swamps roads and spills into low-lying buildings could become more frequent along Pacific coasts of the Americas — a trend El Niño years are expected to accelerate temporarily.