California Braces for Floods as Atmospheric River Threatens

California is bracing for flooding as a so-called atmospheric river delivers a glancing blow to the south of the state, before moving across northern Mexico into the U.S. Southwest this weekend. Coastal flood warnings and advisories are up through Friday as northwest winds push tides nearly 2 feet (61 centimeters) above normal around San Diego and Los Angeles, the National Weather Service said. The higher-than-normal tides are caused in part by the full moon, as well as Kelvin waves produced by the strengthening El Niño. Flood watches have also been issued for central Arizona, including Phoenix through Friday. “California could get something, but it is really farther east of there that we are most concerned about,” said Jennifer Tate, a meteorologist at the U.S. Weather Prediction Center said. “It is going to be potentially heavy rainfall especially for Arizona. The biggest part of the event looks to be Sunday.” Atmospheric rivers are long plumes of moisture traveling thousands of miles across the Pacific and bringing as much water with them as passes through the mouth of the Mississippi River, according to the National Oceanic and Atmospheric Administration. The phenomenon, sometimes called the Pineapple Express by television meteorologists, are ranked on a five-step scale with category one and two storms actually being beneficial and those above three more destructive. The forecast shows California will be spared a direct hit from the atmospheric river set to arrive in the next few days, the Center for Western Weather and Water Extremes said. Parts of Mexico’s Baja California could see up to a category three and four event and this is what will carry the downpours into Arizona, where there is a 15% chance of excessive rainfall Saturday into Sunday, the Weather Prediction Center said. Southern California has a 5% chance of excessive rain through the same time period. Downtown Los Angeles will see its greatest chance for rain Saturday night and the entire county may get from 0.5 to 1.5 inches through the weekend. The National Weather Service warns parents to “have backup event plans ready to go” for the annual Trick or Treat celebrations around Halloween. The strengthening Pacific El Niño typically pours heavy rain into the southern U.S. from California to Florida, which raises the risks of flooding, mudslides and property damage across the Golden State. The chances remain high El Niño will be a historic event that would be the strongest in records dating back to 1950 and that its effects would linger for months. Meanwhile, flood watches are up for almost all of Hawaii’s populated islands where heavy rain was set to fall overnight into Thursday, the National Weather Service said. There is a chance for flash flooding, roads being closed and landslides. Top photo: A Pacific Ocean wave breaks near a worker using heavy equipment to protect damaged beachfront homes in Dana Point, California in September. Bloomberg. Copyright 2026 Bloomberg. Topics California Flood