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By Amanda Greenwood
Associate News Editor
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Flash flood warnings have been issued in Southern California as Storm Rachel brings heavy rain to the region, with forecasters warning of flooding and potentially "life-threatening" rip currents.
The National Weather Service (NWS) said periods of moderate to heavy rain would affect San Diego County, as well as the mountains and deserts of Riverside and San Bernardino counties, through Sunday.
Rainfall rates could reach 0.50 to 0.60 inches per hour along the San Diego coast and valleys, 0.50 to 0.70 inches per hour across desert areas and 0.70 to 1 inch per hour in the mountains, according to the NWS Flood Watch. The heaviest rainfall was expected through early Sunday afternoon before tapering off from south to north.
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The NWS warned that excessive runoff could flood rivers, creeks, streams, and other low-lying and flood-prone locations, while mountain areas could see an increased risk of rockslides and mudslides.
Rachel is also causing hazardous conditions along the Southern California coast. A coastal flood warning covers the coastal areas of San Diego and Orange counties, where significant coastal flooding and beach erosion are considered likely.
The NWS said Rachel's increased swell, onshore winds, and high tides locally above 7.5 feet would combine to produce the greatest impacts Sunday morning. Surf of 5 to 7 feet, with local sets up to 9 feet, is also expected.
This bout of extreme weather comes as attention increasingly turns to the developing El Niño and what it could mean for California this winter.
The latest outlook from NOAA's Climate Prediction Center (CPC), issued on October 8, said El Niño "continues to strengthen,” and is more than 83 percent likely to remain a “strong to very strong event” through January to March 2027.
The agency said there’s also a high chance that this El Niño could become an historic event, which could be stronger than previous El Niños dating back to 1950.
What Is El Niño?
The NWS describes El Niño as the warm phase of a natural climate pattern known as the El Niño-Southern Oscillation, or ENSO. It’s characterized by unusually warm ocean surface temperatures across the central and eastern tropical Pacific.
These changes in the Pacific can disrupt normal winds and rainfall patterns and have a huge impact on weather much further afield.
In its recent October update, the CPC said that sea-surface temperature anomalies exceeded 4 degrees Celsius above normal in parts of the Pacific Ocean, near the equator and closer to the Americas, in September.
What Could El Niño Mean for California?
For California, the primary concern is an increased prospect of a wetter winter, particularly in the southern half of the state.
The CPC's current seasonal forecast favors above-average rainfall across the southern half of California during October, November, and December, extending east and northeast across much of the Four Corners region and Great Plains.
The NWS's California El Niño guidance says the phenomenon can change the track of global storms and increase the amount of rainfall during winter storms. These extended periods of heavy rain could increase the risk of sudden flooding and overwhelm drainage systems.
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The NWS warns that heavy rainfall could destabilize waterlogged slopes, raising the risk of landslides, particularly across steep hillsides and areas affected by wildfires. Along the coast, El Niño-related winter storms could bring powerful waves and storm surge, an abnormal rise in sea level caused by a storm. Warmer-than-normal waters could also contribute to higher ocean levels, worsening coastal flooding and erosion during high tides.
There could also be consequences for the Sierra Nevada.
The NWS says warmer storms could mean more rain instead of snow at lower elevations, although higher parts of the Sierra Nevada could still see heavy snowfall.
When Will California Feel Its Effects?
The latest outlook says El Niño is expected to continue strengthening through the end of 2026, with a strong-to-very strong event likely through the January-March 2027 period.
NOAA says ENSO usually has a strong influence on the U.S. climate between December and February. Historically, El Niño generally shifts the odds towards wetter and cooler-than-average conditions across much of the southern United States.
In summary, Storm Rachel comes as a strengthening El Niño raises concerns about California's weather in the months ahead, with forecasters warning that the climate pattern can increase the likelihood of heavy winter rainfall and flooding.
Newsweek has reached out to the NWS/NOAA for comment and is awaiting a response.
Newsweek’s reporters and editors used Martyn, our AI assistant, to produce this story. Learn more about Martyn here.
Contact Newsweek editors on this story: Ben Kelly and Trevor Davies
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