Coastal communities in Southern California are currently evaluating the damage sustained from recent waves and flooding, even as conditions are expected to worsen with the approach of a "coastally trapped Kelvin wave."
Homes from south Orange County up to Malibu have experienced flooding and severe damage. The coastline from Carlsbad to Long Beach has been significantly affected by erosion.
Laguna Beach, Dana Point, and Carlsbad declared local states of emergency last week. These declarations cited coastal erosion and sand loss, effects attributed to a south swell generated by Hurricane Marie. This aligns with the typical pattern for El Niño, which often leads to a more active hurricane season in the eastern Pacific, where Hurricane Marie originated.
Laguna Beach City Manager Dave Kiff indicated that Laguna's damage was among the most significant compared to other cities along the coast. He noted that city managers from various municipalities expressed concerns regarding sand and the need for sand replenishment. Existing sand replenishment initiatives span from Newport to Huntington and Seal Beach, with others located further south.
Orange County officials announced the activation of their emergency operations center, a measure required when two cities within the county declare local emergencies. Orange County Board of Supervisors Vice Chair Katrina Foley stated that coastal cities are enduring serious damage, prompting the county to mobilize its emergency response efforts.
Further south, transportation officials shared video evidence illustrating severe erosion threatening the Metrolink train tracks in San Clemente. The footage depicted strong ocean waves crashing against the tracks, with sediment crumbling onto the rocks below. Metrolink emphasized the gravity of the situation, calling it "that serious."
In San Diego County, Carlsbad also declared a local emergency in an effort to protect Carlsbad Boulevard, also known as Old Highway 101, from severe erosion.
Scientists have understood the existence of coastally trapped Kelvin waves for decades, recognizing their fundamental link to El Niño. El Niño is a climate pattern characterized by the warming of ocean waters in the central and eastern equatorial Pacific, which in turn influences global weather patterns. Michael Jacox, a research oceanographer with NOAA’s Fisheries’ Ecosystem Science Division, explained that "coastally trapped" waves must follow a coastal boundary, keeping the shoreline to their right in the Northern Hemisphere.
Recent advancements in computational capabilities have enabled scientists, including Dillon Amaya, an expert in these waves and an assistant professor at North Carolina State University, to model and track them in real time. Amaya noted that the current El Niño is among the largest on record, correlating with some of the largest coastally trapped waves recorded.
As El Niño develops, the typical east-to-west trade winds along the equator weaken or can even reverse. This allows large volumes of warm water and high sea surface heights, which usually reside in the far western equatorial Pacific, to move eastward. This warm water, often found around Indonesia, is pushed by equatorially trapped Kelvin waves towards typically cooler parts of the Pacific, near Peru, remaining confined along the equator.
Upon reaching South America, a Kelvin wave divides, with one part heading north towards California, where it then becomes coastally trapped. Jacox explained that along the coast, these waves raise sea levels, increase ocean temperatures, and push cold, nutrient-rich waters deeper below the surface.
Kelvin waves are capable of elevating sea levels by approximately 6 to 12 inches, with these effects potentially lasting for months. Amaya cautioned that these elevated sea levels, when combined with passing weather or storms, can substantially increase the risk of flooding and beach erosion.
The coastally trapped Kelvin wave is currently off the west coast of Mexico. Amaya projected that the wave would enter the Gulf of California around Saturday. From there, it is expected to take about 11 days to navigate the gulf's U-shaped coast, followed by another seven days to travel from Cabo San Lucas at the southernmost tip of the Baja California peninsula to San Diego. Subsequently, it is estimated to take two to three days to reach Los Angeles, and an additional two to three days to arrive in San Francisco. This timeline places the wave's arrival in Southern California in early October, though the precise timing remains uncertain.
Amaya described these waves as "pretty epic," noting their journey of roughly 15,500 miles from the western equatorial Pacific to the Gulf of Alaska, a process that takes about 120 days. While not a surfable wave or overtly noticeable to swimmers or boaters, it is expected to increase the sea level off the California coast by an additional 6 inches, with effects that could persist for months.
Jonathan Warrick, a research geologist with the U.S. Geological Survey, highlighted the significant impact another 6 inches of sea level rise could have, especially when combined with a storm. He recalled recent events where hurricane-generated swells and high tides battered homes across Southern California, causing extreme damage. Warrick stated that when the water level is significantly higher than expected, it can "really wreak havoc." California has already experienced about a foot of sea level rise over the past 125 years due to human-caused global warming and melting polar ice caps, and has also recently seen abnormally high tides.
