A Kelvin wave driven by El Niño could raise California sea levels by a foot for months, heightening coastal flood risks as Newsom declares an emergency.
A slow-moving underwater surge known as a Kelvin wave is advancing across the Pacific toward the U.S. West Coast, and scientists warn it could lift sea levels along California’s shores by six inches to a full foot while a strengthening El Niño lingers.
The Sun reported the wave hit the northern tip of South America in late August and began tracking toward California, raising the prospect of dangerous coastal flooding and heavier beach erosion in the months ahead.
Forecasters have also warned that the developing El Niño could rank among the strongest on record. California Gov. Gavin Newsom responded on September 21 by proclaiming a state of emergency so officials can mobilize resources for what could become a wetter, more intense winter.
Kelvin waves form when trade winds across the equatorial Pacific slow or reverse during El Niño years. Those winds normally blow from South America toward Asia. When they ease, warm water piles up and rolls east in a giant, slow-moving slosh that can span thousands of miles.
Meteorologist Blake Mathews described the process in plain terms to NewsNation.
"It’s an underwater wave that is caused by the slowing of the trade winds across the equatorial waters of the Pacific,"
Mathews said. He offered a simple picture of the mechanics:
"Think of it like water in a bathtub. You put a large fan on one end of the tub and turn it on and the water begins to move to the opposite end,"
He continued:
"Once the fan is turned off, the water begins to flow back to where it came from. That’s a Kelvin Wave in a nutshell."
Once that mass of warm water settles along the California coast, El Niño can trap it there. Sea levels then stay elevated for months rather than dropping after a single storm.
Nate Mantua, a research scientist at NOAA’s Southwest Fisheries Science Center, told The Guardian what that combination means in El Niño winters over the northern Pacific.
"In the El Niño winters in the northern Pacific, we tend to have a lot of storminess, we tend to have more storms and big storm waves in the ocean than we typically do,"
Mantua said. He added:
"So you add that on top of this elevated sea level... then you just expose places to more of the ocean’s energy and simple inundation."
In short, the same storm hits harder when the baseline water level is already higher. Waves travel farther inland. Beaches erode faster. Low-lying stretches flood more easily.
Kate Huckelbridge, head of the California Coastal Commission, made the tide problem explicit in a memo reviewed by The Guardian.
"A key observation from past El Niño events is that the most damaging storms are often those that coincide with the highest tides,"
Huckelbridge wrote. She continued:
"Storms that peak during high tides are far more likely to cause damage than if the same storm peaked during low tide."
That is the practical risk for coastal towns: a foot of extra water underfoot, plus storm waves timed with high tide.
Newsom’s September 21 proclamation does not stop the ocean. It is designed to free up state resources before the wet season deepens. The Kelvin wave’s exact arrival window along California remains partly prospective in the available accounts, and no confirmed flood deaths, injuries, or measured damages from this specific wave were reported in the initial coverage.
What is on the record is the forecast range itself, six inches to a foot of elevated sea level for months, stacked on top of an El Niño that forecasters say could become historically strong. Coastal residents and local taxpayers are the ones who will live with flooded roads, chewed-up beaches, and storm repairs if those warnings hold.
Natural cycles still set the terms. California’s leaders can declare emergencies and move money; they cannot repeal a Pacific Kelvin wave or the winter storms that ride in behind it.
