Officials warn of simultaneous flood, debris-flow, and coastal hazards
On a cloudless autumn afternoon last week, sunlight sparkled on the water that had quietly swallowed a busy intersection to the north of San Francisco, as the surrounding rush-hour traffic slowed to a painful crawl. There were no crashing waves or storm surges to blame for the flood. Marin County was one of many areas up and down the California coast affected by high tides last week, as parts of the Pacific swelled with excess warmth.
The submerged streets stood as an early signal of California’s vulnerabilities as it braces for what could be a tumultuous winter.
“If you think this is bad, just wait until December,” a state worker grumbled as he directed swarms of cars past the choke point toward a sidestreet.
Experts have warned that a potentially historic El Niño is brewing, with the power to unleash extreme weather around the world. The climate phenomenon, characterized by warmer than average equatorial sea surface temperatures, is already under way, according to federal forecasters, and it is expected to strengthen through the northern hemisphere’s autumn and winter.
California is poised to be in its crosshairs. Landslides, flash floods and encroaching sea levels are all on the menu – and they could all happen at once.
“What we’re really looking at is the compounding element,” said Nick Brubaker, the chief resilience officer for the office of emergency management in Marin County. “The biggest concern isn’t just rising tides. It’s the way everything could collide.”
“We are trying to make sure that people are aware that this may be one of the most significant El Niño years that we’ve seen,” Brubaker said.
Dangerous spikes in temperature are likely. Some areas could see supercharged storms and relentless rains. Others face explosive surf, strong currents and devastated marine ecosystems. The effects of El Niño will add an additional foot of sea level rise in California on top of the 8 to 12 inches caused by the climate crisis there over the last century, according to Anderson.
In recent wildfire burn scars, including the slopes of Big Sur that burned this summer and neighborhoods devastated by the 2025 firestorm in Los Angeles, there will be higher chances of debris flows.
Preparations are already under way at all levels of government as officials work to secure vital infrastructure, preset response resources and inform the public of the incoming hazards.
California stretches across roughly 770 miles, and its regions are likely to experience El Niño very differently. Southern California typically sees wetter winters in El Niño years, but that’s not necessarily the case further north.
While the stage may be set for violent weather, it’s impossible to forecast what will unfold. “What the science supports is elevated risk,” said Dr. Ariel Cohen, a meteorologist for the National Weather Service, during a recent briefing held in Los Angeles. “A strong El Niño shifts the probabilities – it does not determine exact outcomes.”
With the potential for dangerous conditions already rising, emergency managers are planning for the worst.
Newsom issued a state of emergency on September 21 to mobilize state efforts and resources, kicking off a flurry of activity. Adverse conditions fueled by El Niño are already taking shape. A mass of warm water known as a Kelvin wave is crawling up the California coastline with the ability to raise sea levels by up to a foot.
Along with coastal flooding from elevated sea levels and high tides, powerful storms swirling through the Pacific have made for an unusually busy tropical cyclone season. Hawaii is still recovering from a series of deluges and strong winds that flooded roads and buildings, unleashed landslides and toppled trees. Swathes of the Southern California coastline have been hammered by massive waves that damaged homes and devoured beaches.
Areas already hit hard are working to recover – and build resilience. In Long Beach, just south of Los Angeles, the seawall has been lined with large sandbags to reinforce spots where strong surf has burst through. In Orange County, roughly 690,000 cubic yards of sand is being pushed along the coastline. Workers are going door-to-door in San Diego’s flood zones to help small businesses ready their buildings.
The Los Angeles County public works department has been assessing risks over the last six months, according to Mark Pestrella, its director, who said flood control systems are ready and optimized during a recent briefing.
Channels and debris have been cleared from drainages, 14 dams were tested and reservoirs prepared. These systems, he clarified, are designed to withstand a so-called 100-year event, which he said had a roughly 1% chance of occurring in any given year. But El Niño could bump those chances higher.
“We are assuming it is going to rain and with El Niño we assume it is going to rain with high intensity,” Pestrella said.
Of particular concern, he added, are the areas still recovering from the wildfires that swept across LA County in January 2025, destroying more than 16,000 structures. In Pacific Palisades and Altadena, the communities most intensely affected, homes and buildings are still being rebuilt. Pestrella said it takes five years for watersheds and hillsides to heal enough to withstand strong rains.
Along LA County’s 23 miles of coastline, large berms and sand dune systems are being built on beaches to fight against erosion, according to Gary Jones, the director of Beaches and Harbors. Officials are starting that work a month and a half earlier than usual.
“This El Niño won’t be the last one and unfortunately erosion at our beaches is becoming more and more common,” Jones said.
Kevin McGowan, director of LA’s office of emergency management, is juggling hazards on the other end of the spectrum: high heat and fire risks that are likely to linger into November.
“We are in the middle of fire season and about to head into a significant heatwave,” McGowan said before a sweltering October weekend that smashed several records across Southern California, noting that fire conditions can still peak through the winter months. “People should continue to prepare not just for one hazard – but all hazards.”
In San Francisco, elevated flood risks around the port and the Embarcadero on the Bay side, and dangerous ocean conditions along the beaches, could be accompanied by long power outages during storms, according to Mary Ellen Carroll, the executive director of the city’s department of emergency management. For older people and those who are medically dependent, “it can get very dangerous quickly,” she said.
Record high tides are likely between December and February next year, with California king tides — when surf is highest — expected during the week of Thanksgiving, the week of Christmas, and on the Martin Luther King Jr. long weekend, making for what officials described as a potentially dangerous holiday season.
“It feels like I’m planning for an earthquake, but I’ve gotten two months’ notice,” Carroll said of the preparation window.
In Marin County, where low-lying areas flood even without El Niño’s added influence, Brubaker said the county is rushing to clear drains and culverts and install temporary flood barriers. Officials have expanded supplies of free pre-filled sandbags and built online tools so residents and visitors can visualize their risks.
In Santa Cruz, emergency services manager Meredith Albert said this year’s preparations build on the challenges coastal communities have long faced. “We are building on what we all know have been our risks and hazards all along – for better or worse, they aren’t a surprise,” she said.
In 2024, a parade of storms and violent surf knocked out the city’s pier, which only recently reopened. While there is careful consideration of overstating messages and emergency alert fatigue, Albert added that “the public messaging is ready to go. The sandbags are ready.”
But the biggest priority is ensuring preparedness starts at the individual and neighborhood levels “and grows outward from there,” Albert said.
“Those community connections are the difference between a disaster being something you can’t come back from and something you can learn from,” Albert said.
Statewide, McGowan said the limits of government response mean community-level support will be critical. “We are never going to have enough resources at the onset of a disaster to support every single person,” he said. “Our communities are the fabric that gets us through these disasters – neighbors helping neighbors saves lives.”