Technology and Science14 September, 20263 min read
Coastally Trapped Kelvin Wave Floods and Erodes Southern California, Triggering States of Emergency
This article is an automated aggregation of coverage from news outlets. Our editorials offer in-depth analysis curated by the NewsCord team.
Kelvin waves move along Mexico's coast toward Southern California, driven by El Niño. Expected to arrive in early October, triggering coastal flooding and erosion.
Kelvin wave nears SoCal
Southern California communities from south Orange County to Malibu are assessing damage as a “coastally trapped Kelvin wave” brings flooding and severe erosion, with Laguna Beach, Dana Point and Carlsbad declaring local states of emergency last week.
“Homes from south Orange County to Malibu were flooded and severely damaged.”
The Los Angeles Times reported that erosion chewed away the coast from Carlsbad to Long Beach, and Orange County officials activated their emergency operations center after two cities in the county proclaimed a local emergency.
Transportation officials posted a video showing severe erosion jeopardizing the train tracks used by Metrolink in San Clemente, with strong ocean waves crashing on the tracks and sediment crumbling onto the rocks below, and Metrolink said, “It is that serious.”
In San Diego County, Carlsbad declared a local emergency in an effort to save Carlsbad Boulevard, also known as Old Highway 101, from severe erosion as the wave moves up the coast of Mexico toward the U.S. West Coast.
The Los Angeles Times said government forecasters put “a 75% chance” that this latest El Niño will be stronger than any other since 1950, and NOAA’s Climate Prediction Center said there is a “98% chance” El Niño will be “very strong” for the three-month period ending in December.
How the wave works
The Los Angeles Times explained that Kelvin waves are “fundamentally at the heart of El Niño,” and that “coastally trapped” Kelvin waves must follow a coastal boundary, with the shoreline to their right in the Northern Hemisphere. NOAA research oceanographer Michael Jacox said, “Along the coast, these waves elevate sea levels, increase ocean temperatures, and push cold, nutrient-rich waters deeper below the surface,” describing how the waves can raise sea levels by as much as 6 to 12 inches potentially for months. The Sacramento Bee described a mass of warm, elevated ocean water hundreds of miles long moving north at roughly 6 mph, currently less than 350 miles from Southern California’s beaches, and said sea levels inside the wave are running roughly 4 to 8 inches above normal.
The Sacramento Bee also said the bulge passed Acapulco in mid-June, Puerto Vallarta in mid-July and the tip of Baja in early August, and that it is centered off central Baja California this week. It projected timing for arrival, saying it will arrive in San Diego by late September, Los Angeles shortly after that, and San Francisco around mid-to-late October, while warning that the wave “quietly raises the baseline the tides ride on top of for weeks or months at a time.”
Flooding, erosion, and timing
KTLA reported that Kelvin waves are slow-moving “humps” of elevated ocean water trapped along the coast, and said Dr. Daniel Swain warned that the “worst-case scenario” would be if “all three of those things, the El Niño Kelvin wave sea level elevation, peak king tide high tide and a significant storm, line up.”
“That would probably bring record-breaking coastal flooding this year.”
KTLA said Swain warned that if multiple Kelvin waves arrive in quick succession, “the effects of the first wave won’t fully diminish by the time the next one arrives,” and it described the waves as only about 6 to 18 inches tall.
The Los Angeles Times said the winter is expected to bring more damaging storms and framed the coastally trapped Kelvin wave as moving up the coast of Mexico and soon hitting the U.S. West Coast.
La Opinión reported that specialists warned sea level in Southern California could rise in the coming weeks due to a Kelvin wave, and quoted Dr. Dillon Amaya saying, “when the sea level rises so much in such a wide area, it takes between three and six months to return to normal.”
La Opinión also said Amaya described Kelvin waves as raising the sea level between 6 and 12 inches (15 to 30 centimeters) above its usual level, increasing the risk of coastal flooding, and it placed the wave “currently located off the coast of Mexico, moving north at six miles per hour,” expected to reach the California coast in early October.