Coastal communities across Southern California are currently assessing damage from recent waves and flooding, even as they brace for potentially destructive conditions from an approaching “coastally trapped Kelvin wave.” Homes from south Orange County to Malibu have experienced flooding and severe damage, while erosion has impacted the coast from Carlsbad to Long Beach.
Laguna Beach and Dana Point in Orange County, along with Carlsbad in San Diego County, recently declared local states of emergency. These declarations cited coastal erosion and sand loss attributed to a south swell generated by Hurricane Marie. El Niño conditions are typically associated with an unusually active hurricane season in the eastern Pacific, where Hurricane Marie formed.
Laguna Beach City Manager Dave Kiff noted that while cities up and down the coast experienced varying levels of damage, Laguna's was "among the greatest, or most significant." Kiff added that concerns about sand and the need for sand replenishment projects, including those from Newport to Huntington to Seal Beach and further south, were common among city managers. Following these declarations, Orange County officials announced the activation of their emergency operations center, a required response when two cities within the county proclaim a local emergency. Orange County Board of Supervisors Vice Chair Katrina Foley affirmed that "Our coastal cities are experiencing serious damage, and the county is mobilizing our emergency response."
The impact on infrastructure is also significant. Transportation officials shared video evidence of severe erosion jeopardizing Metrolink train tracks in San Clemente, where strong ocean waves were seen crashing onto the tracks and sediment crumbling below. Metrolink underscored the severity of the situation in its post, stating, "It is that serious."
Until recently, Kelvin waves were largely an obscure concept, but they are fundamental to El Niño, a climate pattern involving ocean water warming in the central and eastern equatorial Pacific, leading to global weather changes. Coastally trapped Kelvin waves, which must follow a coastal boundary with the shoreline to their right in the Northern Hemisphere, have been understood by scientists for decades, according to Michael Jacox, a research oceanographer with NOAA's Fisheries' Ecosystem Science Division. Advanced computational capabilities now allow scientists like Dillon Amaya, an expert and assistant professor at North Carolina State University, to model and track these waves in real-time. Amaya noted that we are currently experiencing "one of the largest El Niños on record," which is expected to coincide with some of the largest coastally trapped waves on record.
As El Niño develops, typical east-to-west trade winds along the equator weaken or even reverse. This allows warm water and high sea surface heights to shift from the far western equatorial Pacific to the east, near Peru, propelled by equatorially trapped Kelvin waves. Upon reaching South America, these waves split, with one branch traveling north towards California, becoming a coastally trapped wave. Jacox explained that along the coast, these waves elevate sea levels, increase ocean temperatures, and push cold, nutrient-rich waters deeper.
These Kelvin waves can raise sea levels by as much as 6 to 12 inches, with effects potentially lasting for months. Amaya indicated that elevated sea levels, when combined with passing weather or storms, can significantly increase the risk of flooding and beach erosion. The coastally trapped Kelvin wave is presently off the west coast of Mexico and was anticipated to enter the Gulf of California around a recent Saturday. From there, it is estimated to take about 11 days to traverse the gulf's U-shaped coast, and another seven days to travel from Cabo San Lucas to San Diego. It would then take an additional two to three days to reach Los Angeles, and a further 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," traveling approximately 15,500 miles from the western equatorial Pacific up to the Gulf of Alaska over about 120 days. While not a surfable wave and not overtly noticeable to swimmers or boaters, it is expected to increase the sea level off the California coast by an additional 6 inches or so, with effects that could endure for months. This increase, though seemingly minor, could further impact the already damaged California coast, particularly if it coincides with a storm. Jonathan Warrick, a research geologist with the U.S. Geological Survey, highlighted the critical nature of such water level increases, noting that when the water level is a foot or more higher than expected, it can cause severe damage to homes. California has already experienced about a foot of sea level rise over the last 125 years due to human-caused global warming and the melting of polar ice caps, and abnormally high tides have also been observed recently.
