Coastal flooding impacted homes and roads this week from Newport Beach, extending to Long Beach, due to a highly unusual combination of meteorological and oceanic events. Scientists indicate this event offers insights into the challenges California's coast faces amidst predictions for a "super" El Niño winter.
The flooding was attributed to several converging factors: swells from Tropical Storm Rachel, unusually high tides, a record-hot ocean, and an El Niño-fueled Kelvin wave. Jonathan Warrick, a research geologist with the U.S. Geological Survey, described the situation as "unprecedented," noting that this combination may become more frequent in the future due to an extended El Niño season and continued sea level rise.
Newport Beach temporarily closed its beaches and piers in response to the approaching Tropical Storm Rachel. A National Weather Service coastal flood warning encompassed Orange County beaches, among others, through Sunday. The highest flooding risks along the Orange County coast were projected for Sunday morning as swells, onshore winds, and high tides converged. The high tide in Newport Beach on Sunday morning was recorded at 9:48 a.m.
The core of Rachel was anticipated to make landfall in northern Baja California. Its effects, combined with the other oceanic conditions, raised concerns about coastal damage. Warrick highlighted that this week's occurrences could provide clues for the upcoming winter, stating, "This is exactly the type of event that will be seeing a lot more of in the coming decades" with sea level rise.
A significant contributor to the elevated sea levels was an El Niño-fueled Kelvin wave, which traveled slowly up the coast from Peru. This type of wave is not visible at the surface but can raise background sea levels by approximately 6 to 12 inches, also bringing warmer waters that contribute to increased sea volume. Dillon Amaya, an expert on Kelvin waves and an assistant professor at North Carolina State University, noted that while the hurricane was the direct "triggering factor" for storm surge, the Kelvin wave likely "conditioned the background sea state such that flooding was more dangerous this time."
This particular Kelvin wave is expected to maintain elevated sea levels for several months, with another Kelvin wave already being monitored as it approaches the coast of Mexico. City officials, including those in affected coastal communities, undertook preparations for Tropical Storm Rachel, constructing sand berms and fortifying vulnerable areas with sandbags.
Looking ahead, the National Oceanic and Atmospheric Administration’s Climate Prediction Center reported a near 100% probability that this El Niño season will be categorized as "very strong." There is also an 83% chance it could be the strongest on record since 1950. Historically, two of the strongest El Niños in the past 75 years resulted in extensive damage to the Southern California coast. A notable instance occurred in September 1997 when Tropical Storm Nora, during a "very strong" El Niño, sent breakers crashing into beachfront properties in Seal Beach, seriously damaging three homes and causing minor damage to 45 others. Such events are prone to occur during peak high tides around the summer and winter solstices, with especially large tides expected around Thanksgiving, Christmas Eve, and January 22, intensifying the risk of coastal erosion and flooding if they coincide with strong winter storms, according to Reinhard Flick, a researcher at the UC San Diego Scripps Institution of Oceanography.
Mark Merrifield, director of the Scripps’ Center for Climate Change Impacts and Adaptation, added that around Christmastime, California is expected to experience very strong king tides that will add to the high sea levels caused by El Niño.
