Southern California is bracing for a significant threat to its coastline as a “coastally trapped” Kelvin wave makes its subtle but impactful arrival, according to climate scientists. This aquatic pulse, which has been slithering up the coast for weeks, is expected to add between 6 to 12 inches to background sea levels, a condition that could persist for months.
While not visible like crashing surf, this sea level rise is a major concern when combined with other factors, potentially exacerbating issues for California coastal cities and property owners. UC Agriculture and Natural Resources climate scientist Daniel Swain noted that the arrival is a gradual increase rather than a singular moment, as the ocean height builds over time.
Dillon Amaya, an assistant professor at North Carolina State University, predicted the wave’s arrival in San Diego this week, followed by Los Angeles days later. Amaya cautioned that the Kelvin wave alone will not cause flooding, but it could significantly intensify damages if combined with forecasted storms or high tides.
This convergence is expected soon. Southern California is anticipated to face southerly swells from a distant Hurricane Rachel starting Wednesday, peaking Thursday and Friday. The National Weather Service (NWS) warns that coastal flood impacts will likely surpass those from late September’s Hurricane Polo, though less severe than Hurricane Marie, which damaged coastal homes in Dana Point, Long Beach, and Malibu over Labor Day weekend.
Areas particularly susceptible to coastal flooding this week include the Long Beach peninsula, especially vulnerable to southerly swells. The NWS office in Oxnard also raised concerns for the coast between Malibu and Ventura, and Catalina Island.
This immediate threat comes amid a strengthening El Niño, a climate pattern characterized by heating ocean waters in the central and eastern equatorial Pacific. El Niño not only influences global weather but can also wreak significant havoc on the coastline, often bringing higher sea levels. Scientists warn that a strengthening El Niño could lead to the highest sea levels ever recorded on the California coast this year, dramatically increasing the risk of widespread and damaging flooding.
Kristan Lund, a meteorologist with the NWS office in Oxnard, explained that thermal expansion from warm El Niño sea surface temperatures, combined with Kelvin waves and incoming swells, all contribute to rising ocean heights. The federal Climate Prediction Center estimates a 75% chance that the current El Niño will be stronger than any recorded since 1950. Previous strong El Niños have led to significant damage and coastal erosion.
Indeed, sea levels are already notably above official tide forecasts, which do not account for El Niño. For instance, Santa Monica recorded tides 11 inches above forecast this week. Daniel Swain has reported receiving calls from harbor masters and fire chiefs regarding “king tide-like flooding,” urging preparation for what may come later this fall and winter.
In response to the anticipated impacts, Governor Gavin Newsom declared a state of emergency last month to mobilize state resources for potential strong storms and coastal flooding, urging Californians to take the situation seriously. Coastal communities across Orange County have already taken action, with Los Angeles County, the city and county of San Diego, Orange County, Long Beach, Dana Point, Laguna Beach, San Clemente, Malibu, and Carlsbad all declaring local emergencies related to El Niño, coastal erosion, or recent hurricane swells.
Significant beach erosion has been reported in Orange County cities such as Laguna Beach, Newport Beach, and San Clemente. Recent strong surf has already caused damage, including to Dana Point homes. With ocean temperatures off the Southern California coast now 7 to 8 degrees above average, and record heat in the Pacific, residents and city leaders are increasingly turning to large rocks and seawalls to protect homes and vital infrastructure, such as railroads, from falling into the sea. Forecasters are also warning of increased drowning risks this week due to larger waves and strong rip currents, advising residents to check with lifeguards before swimming, as conditions may be dangerously deceptive.
