Hurricane Marie reshaped Southern California’s coastline last week. El Niño could be far worse

The Hurricane Marie-fueled surf that hit Southern California last week was just a taste of the coastal damage El Niño could bring over the next several months, experts warn.

The destructive waves, driven by a weather system hundreds of miles away in the Pacific Ocean, reached 12 feet at times over Labor Day weekend.

The surf damaged beachfront homes from Malibu to Orange County and triggered evacuation orders for dozens more. It also threatened coastal roads and temporarily suspended service along the Pacific Surfliner railway between San Clemente and Oceanside. And coastal emergencies are still in place in Laguna Beach and Dana Point.

But there’s a good chance this was just the beginning.

The National Weather Service says there is a more than 90% chance this year’s El Niño will be very strong. Scientists also predict an alarming convergence of climate forces to come along with it that could push sea levels and surf to record highs this winter.

Coastal erosion from these atmospheric forces could come even sooner, however, with El Niño-related sea level rise expected to hit Southern California as soon as Oct. 1.

Here’s a look at the factors experts say are converging with potentially devastating effects.

Kelvin waves

First, let’s talk about Kelvin waves.

Kelvin waves are large masses of warm water that move across the ocean, driven by the same high water temperatures near the equator that are behind the wider El Niño climate pattern.

In this case, the wave first moved eastward along the equator until it ran into Central and South America, where the landmass forced it to head north. Now, it’s working its way toward Southern California.

Kelvin waves bump up the sea level about 6 to 18 inches over a large area. In the open ocean, they aren’t particularly noticeable to the naked eye. Scientists use specialized equipment to detect them.

But when pushed up against the coast, they can create much more substantial sea level rise, and scientists say this Kelvin wave is likely to reach the Southern California coast by early next month.

This graphic shows the sea surface heights over 45 days between August and September as the Kelvin wave hit South America, then began its journey north along the coast of Central America. These number are compared to the 1993-2025 baseline sea levels over 45 days between August and September.

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Dillon J. Amaya

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High sea levels push waves farther inland, where they crash against the shoreline with greater force, making erosion worse.

“ Boy, if you have enough water level to support those waves so they dump right on your coast, they're right there,” said Timu Gallien, a UCLA environmental engineering professor who studies coastal erosion. “Now they're coming through your window, now they're on your front porch, quite literally, for the beachfront homes.”

Scientists also say multiple Kelvin waves are likely to come in a sequence, become trapped against the coast and build up sea levels even more.

King tides

El Niño’s warm oceans cause elevated sea levels on their own because warm water takes up more space than cold water. When combined with natural high tides, levels are raised even higher, creating destructive king tides.

This year, by late fall and winter, tides are projected to be at their highest levels in 18 years due to the natural cycle of the moon and planets.

Sea-level rise from the nearly decade-high tides is likely to combine with El Niño’s surge.

“That rides on top of the tide,” Gallien said. “ You've got the tides that are going up and down, then you've got this El Niño signal that goes up and down on top of that tide.”

Storms

Warm El Niño waters also drive storms, and scientists are predicting some of the highest ocean temperatures ever recorded.

“We're going to be experiencing record-breaking water temperatures for many, many months on end on the top of what is already a record-breaking marine heat wave,” said Daniel Swain, a UC climate scientist, during a webinar on El Niño predictions last week.

Warmer seawater evaporates faster, adding moisture in the air that can turn into rain. El Niño also shifts the jet stream, pushing more moisture into Southern California rather than its normal path toward the Pacific Northwest.

Warm waters also create more tropical storms in the eastern Pacific, making them stronger and longer lasting.

Like Hurricane Marie, surges from these storms can travel hundreds of miles until they slam into the California coast.