California beach communities are expected to see rising sea levels in the coming weeks as El Niño continues to strengthen, with more sand erosion and damage possible, according to new data.
Another El Niño-influenced phenomenon — a “coastally trapped Kelvin wave” — is moving up the coast of Mexico and will soon hit the U.S. West Coast.
This isn’t a surfable wave, and it wouldn’t be overtly noticeable to swimmers or boaters either. But it is expected to increase the sea level off the California coast by another 6 inches or so, and its effects could last months, according to Dillon Amaya, an expert on coastally trapped waves and an assistant professor at North Carolina State University’s Department of Marine, Earth and Atmospheric Sciences.
It might not sound like much, but another 6 inches of sea level rise could further bludgeon the already battered California coast, especially if combined with the effects from a storm.
“We saw why that’s important recently, with houses across Southern California getting battered, especially at those high tides. We had hurricane-generated swells and high tides, and the combination was extremely damaging to these homes,” said Jonathan Warrick, research geologist with the U.S. Geological Survey. “When the water level is extra high, a foot or more higher than we expect it to be, then it can really wreak havoc.”
As it stands, the Golden State has already experienced about a foot of sea level rise over the past 125 years from human-caused global warming and the melting of the polar ice caps. And lately, the state has also seen abnormally high tides.
The California coast has also been dealing with a long-lasting marine heat wave unrelated to El Niño, which can also raise the sea level.
“The combination of the wave and El Niño and marine heatwave, all of these all of these factors are contributing essentially another foot of sea level rise — in addition to what we’ve experienced from climate change,” said Amaya, who got his doctorate in oceanography at the Scripps Institution of Oceanography at UC San Diego.
Until recently, Kelvin waves were a pretty obscure concept. But they’re fundamentally at the heart of El Niño: a climate pattern in which the ocean waters in the central and eastern equatorial Pacific heat up and spur changes in the atmosphere that can affect weather around the world.
As El Niño develops, the typical east-west trade winds along the equator weaken or even reverse, “which allows a lot of really hot water and high sea surface heights to slosh back from the far western equatorial Pacific, where they typically sit, all the way to the east,” Amaya said.
That means typically warmer water, like around Indonesia, moves east to a normally cooler part of the Pacific, near Peru — pushed along by Kelvin waves.
Upon hitting South America, the Kelvin wave splits into two, one heading north, toward California.
In the Northern Hemisphere, these Kelvin waves become “coastally trapped,” meaning they have to follow a coastal boundary, with the shoreline to their right, said Michael Jacox, research oceanographer with the National Oceanic and Atmospheric Administration’s Fisheries’ Ecosystem Science Division.
“Along the coast, these waves elevate sea levels, increase ocean temperatures, and push cold, nutrient-rich waters deeper below the surface,” Jacox said.
As they travel, Kelvin waves can raise sea levels by as much as 6 to 12 inches — potentially for months.
“Those elevated sea levels, when combined with passing weather or storms, can substantially increase flood risk and risk for things like beach erosion,” Amaya said.
The coastally trapped Kelvin wave is currently on the west coast of Mexico, perhaps south of Puerto Vallarta. Amaya said he expects the wave to enter the Gulf of California on or around Sept. 19. Once there, it’ll take about 11 days for the wave to hug the gulf’s U-shaped coast and, from there, another seven days for it to travel from the southernmost tip of the Baja California peninsula — Cabo San Lucas — to San Diego.
It’ll then take about two to three days to reach L.A., another two to three more to get to San Francisco.
That would put the wave’s arrival in Southern California in early October, although the exact timing remains uncertain.
“They’re pretty epic. They travel something like 25,000 kilometers [15,500 miles] all the way from the western equatorial Pacific up … to the Gulf of Alaska, and it takes about 120 days,” Amaya said.
Coastally trapped Kelvin waves have been known to exist for decades, as long as scientists have understood El Niño. But computational capabilities have only recently progressed to the point scientists like Amaya have been able to model and track them.
“Now scientists have a way of seeing these things unfold in real time, and not to mention we’re experiencing one of the largest El Niños on record, which is going to correspond with some of the largest coastally trapped waves on record,” Amaya said.
Government forecasters say there’s now a 75% chance this latest El Niño will be stronger than any other since 1950. There is a 98% chance that El Niño will be “very strong” for the three-month period ending in December, the National Oceanic and Atmospheric Administration’s Climate Prediction Center said Thursday.
Temperatures beneath the ocean are significantly above average, in excess of 18 degrees at depth, the center said. That’s the highest such temperature in the modern record of satellite data, according to Michelle L’Heureux, El Niño team lead at NOAA’s Climate Prediction Center.
The upcoming Kelvin wave isn’t the first of this El Niño season, Amaya said. One already passed from the western Pacific to the Gulf of Alaska from early May to mid-June, “and depending on the way you decipher the data, there might have been a second smaller wave that’s already passed passed through,” Amaya said.
The arrival of the Kelvin wave in the coming weeks could exacerbate marine ecosystem impacts already being strained by the ongoing marine heat wave that isn’t related to El Niño, Amaya said. There have been measurements of harmful algal blooms along the California coast already.
During the previous “very strong” El Niño in 2015-16, there were five or six coastally trapped Kelvin waves that made their way up the coastline. The strongest ones occurred in the winter, a period that saw record erosion along the California coast.
“So I do think that there’s a good chance that the strongest coastally trapped waves are ahead of us,” he said.
And the hurricane season in the eastern Pacific Ocean is far from over, which could create additional risks for California. El Niño makes a more active hurricane season in the eastern Pacific more likely. On Thursday afternoon, a new tropical storm, Norbert, was spinning hundreds of miles southwest of Baja California, heading west.
“A very strong developing El Niño event is going to increase the likelihood of late season tropical storms and hurricanes in the East Pacific Ocean, and strengthen the ones that do occur,” UC climate scientist Daniel Swain said last month. “And the more of them there are, and the stronger they are in the tropics, the better the chances of some recurving tropical circulation or remnant moisture making it up to California sometime between August and October.”
