The Kelvin wave bearing down on Southern California this week is not the kind that draws surfers.
You don’t see it crash on shore, and by itself, it’s probably not even noticeable. But it can have a profound effect, adding 6 to 12 inches to background sea levels, potentially for months.
This is a major concern when combined with other sources of sea level rise, and could exacerbate the woes of California coastal cities and property owners.
The “coastally trapped” aquatic pulse has been slithering up the coast for weeks, fascinating scientists and weather watchers as it marched across the equatorial Pacific before splitting upon hitting the coast of Peru.
“It is arriving now,” UC Agriculture and Natural Resources climate scientist Daniel Swain said in an interview.
Swain said there’s not a particular singular moment of arrival. It’s more like “a gradual increase, because the surge, or the bulge in the ocean height itself, is hundreds of miles wide … it takes a while to build.”
Dillon Amaya, an assistant professor at North Carolina State University’s Department of Marine, Earth and Atmospheric Sciences, said last week that he expected the wave would arrive in San Diego in the middle to later part of this week, and in Los Angeles perhaps three days later.
“The Kelvin wave by itself will not cause flooding,” Amaya said. However, “if there are storms forecasted or a high tide coming up, that is when the Kelvin wave could exacerbate damages.”
That could come into play this week. Southern California is expected to face southerly swells from a distant hurricane — Hurricane Rachel — starting Wednesday and peaking Thursday and Friday.
The National Weather Service is warning that coastal flood impacts will probably be more significant than late September’s Hurricane Polo, although less than Hurricane Marie, which shot damaging swells toward a number of coastal homes in Dana Point, Long Beach and Malibu over Labor Day weekend.
The area most susceptible to coastal flooding this week will likely be the Long Beach Peninsula, which is particularly vulnerable to swells coming from the south. Other areas of concern include the coast between Malibu and Ventura, as well as Catalina Island, the weather service office in Oxnard said.
Swells from the west or northwest are also expected soon, too, from another weather system.
Forecasters warned of an increased risk of drownings this week due to larger waves and strong rip currents, and cautioned that the ocean “may be too dangerous for swimming.”
“Make sure you check in with lifeguards to know the conditions, to know if it’s safe to swim,” said Kristan Lund, meteorologist with the National Weather Service office in Oxnard. “It can be pretty deceiving until you’re out there and realize how strong the rip currents actually are.”
The eastern Pacific has weathered an unusually active hurricane season this summer and fall, likely related to the development of a potentially historically strong El Niño. That climate pattern sees the heating of ocean waters in the central and eastern equatorial Pacific, which spur changes in the atmosphere that can affect weather around the world.
While often cast as a rainmaker in Southern California, El Niño can also wreak havoc on the coastline.
The climate pattern also contributes to rising sea levels, since water expands as it heats up. That, combined with seas that have already risen over the past century due to human-caused climate change, puts California’s treasured coast in the oceanic crosshairs.
“We have that thermal expansion from warm sea surface temperatures, from the El Niño — that makes it raise a little bit. The Kelvin waves will make it raise a little bit. And then you have the swell that’s also coming in, making the waves higher,” Lund said.
The federal Climate Prediction Center says there’s a 75% chance that the current El Niño will be stronger than any in the modern record, which dates to 1950. Two of the three strongest on record — in 1982-83 and 1997-98 — coincided with above-average precipitation in California and caused considerable damage. Another very strong El Niño, in 2015-16, did not bring with it above-average precipitation to Southern California, but still brought record coastal erosion.
The imminent arrival of the Kelvin wave comes as California has jolted into emergency mode. Gov. Gavin Newsom last month declared a state of emergency, saying he wanted to mobilize state resources to “prepare for El Niño’s anticipated impacts, like strong storms and coastal flooding.”
“This fall and winter could be dangerous, and Californians should take it seriously,” Newsom’s office said in a statement.
Sea levels are already significantly above the official tide forecasts, which are generated years in advance and don’t account for an El Niño. In Santa Monica, for example, the tides were coming in at about 5 inches above the official forecast from the National Oceanic and Atmospheric Administration as of late August. This week, the tides were coming in 11 inches above forecast.
“I’ve had multiple phone calls from harbor masters and fire chiefs in Southern California over the past week, saying, ‘Why is the harbor flooding? We have king tide-like flooding,’” Swain said in a recent livestream. “And my response has been, ‘You’re exactly right. That’s exactly what we’d expect to see right now. … And if you think it’s a problem now, you might want to be preparing for what could happen later this fall and winter.’”
Scientists have warned that they’re expecting likely the highest sea levels ever recorded on the California coast this season.
Significant beach erosion has already been reported in Laguna Beach, Newport Beach, San Clemente, Carlsbad and Santa Monica — which blamed it for the cancellation of a coastal music festival last month. Municipalities declaring local emergencies related to El Niño, coastal erosion or recent hurricane swells include Los Angeles County, the city and county of San Diego, Orange County, Long Beach, Dana Point, Laguna Beach, San Clemente, Malibu and Carlsbad.
Ocean temperatures off the Southern California coast are now about 7 to 8 degrees above average, Swain said. And it’s record hot in the Pacific from central Baja California to Southern California, he said, citing records that go back to 1982.
The Kelvin wave arriving now is either the second or third one of this El Niño, depending on how you analyze the data, Amaya said. But it’s the biggest so far, according to Swain.
As an El Niño develops, the typical east-to-west trade winds along the equator weaken or even reverse. That allows hotter and higher seas to slosh from the far western equatorial Pacific — like Indonesia — east to a normally cooler part of the ocean near Peru, Amaya said.
As those Kelvin waves hit the coast of the Americas, they are said to become “coastally trapped,” because they have to follow a coastal boundary, with the shoreline to their right in the Northern Hemisphere, according to Michael Jacox, research oceanographer with the NOAA’s Fisheries’ Ecosystem Science Division.
More Kelvin waves are expected later this season, and scientists are concerned about whether one could coincide with exceptionally high king tides, a big storm, or both, raising the risks of a coastal flood.
“We’re probably going to get at least two more major Kelvin waves that will arrive between November and January, during the period of king tides [and] during the period of maximum potential storm activity. This is again, potentially, going to be a significant problem,” Swain said. “I am expecting at this point coastal flooding on par with the kind of flooding we saw in ’82-’83, ’97-’98, ’15-’16.”
People wade through a recreational vehicle park flooded by a king tide on Jan. 3 near Corte Madera in Marin County.
(Ethan Swope / Associated Press)
To be sure, there is always a chance that El Niño may not have the anticipated impact on Southern California.
But Swain and others are betting that it’s unlikely this winter will be boring for California.
“The most likely outcome this winter is that it’s very wet and that there are some episodes of significant flood risk,” Swain said.
The Climate Prediction Center is forecasting above-average precipitation for Southern California during December, January and February.
Swain said he’s less concerned about this week’s Kelvin wave than the prospect of future ones later this year. Already, there are signs another is developing.
“I’m much more concerned about what happens this winter, because we are guaranteed to have king tides. We will have water levels that are at least a foot or two higher than they are now just because of the king tides. So that already is going to produce a worse effect than we’re seeing now. Do we get a big storm during that window? That could really be a big problem,” Swain said.
