California’s coast faces an unprecedented combination of rising sea levels, severe marine heatwaves, and extreme astronomical tides during the autumn and winter seasons, according to federal and academic scientists. The convergence of these factors threatens to trigger widespread coastal flooding, accelerate the erosion of cliffs and beaches, and overwhelm municipal stormwater infrastructure across the state.
El Niño-Driven Sea Level Rise and Ocean Warming
The strengthening El Niño pattern is actively warming waters off the California coast, causing sea levels to rise up to a foot above normal levels, according to Jonathan Warrick, a research geologist with the U.S. Geological Survey (USGS), speaking to the Los Angeles Times. This transient increase compounds decades of historical sea level rise driven by climate change. In the San Francisco Bay, the mean sea level has risen approximately 12 inches over the last 125 years, according to state data.
“This winter is very possible that California will reach the highest sea levels ever recorded,” said Daniel Swain, a climate scientist at the University of California (UC). Mark Merrifield, director of the Center for Climate Impacts and Adaptation at Scripps Institution of Oceanography at UC San Diego, noted via satellite data from NASA that the eastern Pacific’s sea level already sits more than half a foot above the baseline reference point. Furthermore, the marine heatwave designated as NEP25A has remained active since May 2025, keeping ocean temperatures among the highest recorded in the past two decades, per the National Oceanic and Atmospheric Administration’s (NOAA) Integrated Ecosystem Assessment.
Astronomical Tides and Triple Threat Conditions
Compounding the effects of El Niño, California faces a period of exceptionally high tides driven by lunar orbital cycles. Reinhard Flick, a researcher at Scripps Institution of Oceanography, explained to the Los Angeles Times that the 18.6-year lunar nodal cycle and the 4.4-year perigee cycle are currently nearing their maximums. Peak tides for this cycle are projected around Thanksgiving, Christmas Eve, and January 22.
“It looks like around December we are going to witness some of the highest tides that we’ve ever seen in this geologic epoch,” Swain stated. When these extreme astronomical tides coincide with winter storms and elevated ocean heights, low-lying coastal neighborhoods experience severe challenges. Jeremy Smith, an engineer with the California Coastal Commission, noted that low-profile coastal developments risk inundation as high waters and heavy wave action overtop beaches and overwhelm storm drains.
Storm Tracks and Historical Precipitation Impacts
The National Weather Service and NOAA’s Climate Prediction Center have indicated a high probability of a strong El Niño winter, which typically shifts the winter jet stream southward and directs more storm systems toward California. While historical events like the 1982-83 and 1997-98 winters brought double normal precipitation to downtown Los Angeles, subsequent strong events like the 2015-16 winter yielded below-average rainfall in the same area, demonstrating that El Niño intensity does not guarantee uniform rainfall totals statewide. However, the 2023-24 winter brought severe flooding to Ventura, Los Angeles, and San Diego counties, including a wave strike in Ventura that injured eight people.
During these high-energy events, beaches across the state typically retreat inland by roughly 30 meters, according to Merrifield. This landward shift strips away protective sand buffers, leaving coastal infrastructure, residential structures, and seaside cliffs directly exposed to wave action and saltwater intrusion.
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