Coastal communities in Orange County are currently evaluating significant damage from recent high waves and flooding, as Southern California prepares for the potential effects of an approaching "coastally trapped Kelvin wave." This phenomenon, closely linked to the ongoing El Niño climate pattern, is anticipated to increase sea levels and exacerbate existing coastal erosion.
Laguna Beach and Dana Point, both situated in Orange County, recently declared local states of emergency. These declarations cited coastal erosion and considerable sand loss, attributed to a south swell generated by Hurricane Marie. The broader impacts have been felt across Southern California, with homes from south Orange County to Malibu experiencing flooding and severe damage. Extensive erosion has impacted the coastline from Carlsbad northward to Long Beach.
In response to these conditions, Orange County officials activated their emergency operations center. This action is mandated when two cities within the county declare local emergencies. Orange County Board of Supervisors Vice Chair Katrina Foley issued a statement acknowledging the severity of the situation, stating, "Our coastal cities are experiencing serious damage, and the county is mobilizing our emergency response." Further north in San Clemente, transportation officials documented severe erosion threatening the Metrolink train tracks, showing powerful ocean waves crashing directly onto the tracks and sediment crumbling onto the rocks below. Metrolink emphasized the gravity of the situation in its public post, asserting, "It is that serious."
Dave Kiff, Laguna Beach City Manager, commented on the varying degrees of damage along the coast. He noted that Laguna Beach's damage was "among the greatest, or most significant," compared to other cities. Kiff also mentioned ongoing discussions with other city managers regarding "concern about sand and sand replenishment," referencing existing sand replenishment projects from Newport Beach to Huntington Beach and Seal Beach, as well as some farther south.
The impending threat stems from a coastally trapped Kelvin wave, a concept increasingly understood through modern computational modeling. Research oceanographer Michael Jacox from NOAA’s Fisheries’ Ecosystem Science Division explains that "coastally trapped" waves must follow a coastal boundary, with the shoreline to their right in the Northern Hemisphere. These waves are a fundamental component of El Niño, a climate pattern characterized by the warming of ocean waters in the central and eastern equatorial Pacific, which subsequently influences atmospheric conditions globally.
Dillon Amaya, an assistant professor at North Carolina State University and an expert on these waves, highlights that advanced computational capabilities now allow scientists to observe these events in real time. He notes that the current El Niño is "one of 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 even reverse. This allows significant volumes of warm water and high sea surface heights to "slosh back" from the far western equatorial Pacific, where they usually reside, to the east. These movements are propelled by "equatorially trapped Kelvin waves" that remain confined to the equator.
Upon reaching South America, an equatorially trapped Kelvin wave divides, with one part heading north toward California and the other south. At this point, they become coastally trapped. Jacox elaborated on their effects, stating that "Along the coast, these waves elevate sea levels, increase ocean temperatures, and push cold, nutrient-rich waters deeper below the surface." These waves can raise sea levels by as much as 6 to 12 inches, an elevation that could persist for months. Amaya cautioned that "Those elevated sea levels, when combined with passing weather or storms, can substantially increase flood risk and risk for things like beach erosion."
The coastally trapped Kelvin wave is currently located off the west coast of Mexico. Amaya anticipates its entry into the Gulf of California "on or around Saturday." From there, it is expected to take approximately 11 days to traverse the gulf’s U-shaped coastline. Following this, an additional seven days will pass for the wave to travel from Cabo San Lucas, at the southernmost tip of the Baja California peninsula, to San Diego. The wave is then projected to take about two to three days to reach the Los Angeles area, with another two to three days to reach San Francisco. This timeline suggests the Kelvin wave's arrival in Southern California is expected in early October, though the precise timing remains subject to uncertainty. Amaya characterized these waves as "pretty epic," noting their journey of approximately 15,500 miles from the western equatorial Pacific to the Gulf of Alaska, taking about 120 days.
This Kelvin wave is not a surfable wave and will not be overtly noticeable to individuals in the water or on boats. However, its significant effect will be an estimated increase of another 6 inches or so in sea level off the California coast, with effects potentially lasting for months. Jonathan Warrick, a research geologist with the U.S. Geological Survey, underscored the potential impact, stating that an additional 6 inches of sea level rise could "further bludgeon the already battered California coast," particularly if it coincides with a storm. He further explained that "When the water level is extra high, a foot or more higher than we expect it to be, then it can really wreak havoc." California has already experienced approximately one foot of sea level rise over the past 125 years, attributed to human-caused global warming and the melting of polar ice caps, and has recently observed abnormally high tides. The combined effect of these factors presents an ongoing challenge for Orange County’s coastal infrastructure and communities.
