SANTA MONICA, CA — Santa Monica officials are preparing for potentially increased coastal storm activity as an approaching Kelvin wave threatens to raise background sea levels along Southern California's coastline.
The city has 85 properties in the northern section of Pacific Coast Highway within the 100-year flood zone, city spokesperson Cecile Oreste told Patch.
That designation means the properties have a 1 percent chance of experiencing a flood in any given year — not that flooding is expected only once every 100 years. Residents can check individual locations using the Federal Emergency Management Agency's Flood Map Service Center.
"The city is engaged in its regular storm preparedness activities with heightened awareness that there could be increased coastal storm activity and more intense rainfall," Oreste told Patch.
The preparations come as a coastally trapped Kelvin wave associated with El Niño approaches Southern California, potentially raising the starting point from which high tides, large swells and storms act.
Dillon Amaya, an assistant professor of marine, earth and atmospheric sciences at North Carolina State University who has been tracking the disturbance, told Patch on Oct. 1 that the wave was somewhere between Cabo San Lucas and San Diego and could reach San Diego in roughly five to seven days.
Amaya initially estimated that the disturbance could raise coastal sea levels by approximately 6 to 12 inches as it moved north along California. He said last week that the wave had lost some energy during its journey and that he now expects the resulting anomalies to be toward the lower end of that range.
"The wave's energy has attenuated somewhat, so I think the anomalies will be on the lower end of the 6-12 inch range," Amaya said.
NOAA says coastally trapped Kelvin waves are a signature of El Niño. After oceanic Kelvin waves travel east across the equatorial Pacific and reach Central and South America, the disturbances can propagate north along the North American coast. They can produce sea-level changes of approximately 15 centimeters, or 6 inches, measurable by coastal tide gauges and satellites.
The Kelvin wave itself does not cause flooding, Amaya stressed. Instead, it raises background sea levels, increasing the potential impact when other conditions occur at the same time.
"The main thing to realize and understand about this wave is that Kelvin waves by themselves do not cause flooding," Amaya said. "They raise background sea levels, which when combined with high tides, large swells, and storms can substantially increase flood risk."
Even relatively small increases can matter. "I know that doesn't sound like much, but every 2-4 inches of baseline sea level rise essentially doubles the flood risk for low-lying regions of California, when combined with high tides, large swells, and storms, so it is substantial," Amaya said.
Santa Monica's extreme-weather preparedness guidance says California is preparing for a strong El Niño during fall and winter 2026-27. While the climate pattern could mean a rainier winter, the city cautions that is not guaranteed. Potential impacts include prolonged rain, landslides and coastal flooding.
Oreste encouraged residents within the northern PCH flood zone — particularly those who have experienced flooding before — to prepare before rain enters the forecast.
The city provides 10 empty sandbags at any Santa Monica fire station, while free sand for filling them is available at the Clover Park parking lot. Residents can find details on the city's sandbag information page. Oreste also said filled sandbags are available at City Yards during business hours.
The city's published guidance recommends that residents in flood-risk zones consider purchasing flood insurance because flood damage is typically not covered by homeowners insurance, while also keeping gutters and storm drains clear before heavy rain. Santa Monica More information about flood coverage is available through the National Flood Insurance Program's FloodSmart website.
Oreste also urged residents to inspect and repair roofs, gutters and drains and sign up for SMAlerts, which the city uses to distribute emergency information and public-safety instructions.
Santa Monica's recently updated Local Hazard Mitigation Plan details the natural hazards facing the city and measures intended to reduce their impacts. The plan was adopted by the City Council on Nov. 18, 2025, approved by Cal OES and FEMA in spring 2026 and is scheduled to be updated again in 2031.
The city advises people throughout Santa Monica — not just those within mapped flood zones — to follow public-safety directions during storms and stay off roadways when flood or flash-flood warnings are issued. And while the approaching Kelvin wave could help set the stage for coastal flooding, residents should not expect to see the disturbance itself arrive.
"Folks are not going to see this wave whiz by and may not even know it's happened until we get one of these compounding factors to trigger flood conditions," Amaya said.
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