Kelvin wave may raise California sea levels by up to a foot as El Niño intensifies
Scientists say a slow-moving Kelvin wave, amplified by a strong El Niño, could lift coastal water levels in California by as much as one foot through the winter, prompting state emergency preparations.
A planetary-scale oceanic Kelvin wave that began near the northern tip of South America in late August is moving toward the U.S. West Coast and could reach California within days. Researchers warn the wave may elevate sea levels along the California shoreline by up to a foot for several months as the ongoing El Niño keeps warm water trapped near the coast.
"You can follow them along … we see the higher sea levels along the equator, and when the wave reaches the coast of South America, it cannot continue to go eastward," said Severine Fournier, a research scientist at NASA's Jet Propulsion Laboratory. "So it goes north and south."
NOAA scientist Nate Mantua explained that when trade winds weaken during El Niño, the piled-up warm water in the western Pacific sloshes eastward toward California. He noted that while Kelvin waves are a natural, long-standing phenomenon, rising baseline sea levels—about eight inches over the past century—mean the wave adds to an already higher baseline.
"We can predict a lot of the impacts, but not all," Mantua added.
The current El Niño is projected to be the strongest in a millennium, raising concerns about heightened storm activity, storm surges, flooding and coastal erosion. Mike Jacox, an oceanographer at the Southwest Fisheries Science Center, said the combination of higher tides and stronger storms could increase flood risk during the winter holiday period.
In response, California Governor Gavin Newsom declared a state of emergency, mobilizing resources such as road-closure equipment and National Guard support. The California Coastal Commission urged residents to inspect vulnerable properties, improve drainage and address potential damage before severe weather arrives.
"A key observation from past El Niño events is that the most damaging storms are often those that coincide with the highest tides," wrote Kate Huckelbridge, head of the commission.
Mantua cautioned that the exceptional intensity of this El Niño, combined with rising sea levels, could produce damage exceeding that of previous strong El Niño winters in 1983, 1998 and 2016.