California Governor Gavin Newsom declared a state of emergency to mobilize resources ahead of winter storms and coastal flooding. A Kelvin wave is nearing southern California and is expected to reach the San Francisco Bay Area by early October.

The Kelvin wave is expected to raise sea levels along the California coast by up to one foot. This surge arrives as part of a broader pattern driven by El Niño conditions, which involve a massive movement of warm water across the Pacific that collides with the South American coastline and surges north. Kelvin waves do not crash like typical ocean waves but swell tides from beneath the surface, creating conditions for higher sea levels to linger.

Governor Newsom proclaimed a state of emergency in California on September 21, 2026, to prepare for the impacts of a historic El Niño event. The declaration aims to bolster preparedness against flooding, landslides, and coastal risks. The California Governor’s Office of Emergency Services has been coordinating statewide preparedness activities for potential severe weather, flooding, coastal flooding, erosion, mud and debris flows, and related impacts associated with the El Niño event, as outlined in the signed state of emergency proclamation.

The California Office of Emergency Services (CalOES) has coordinated with 48 local governments to pre-position 500,000 sandbags and secure critical infrastructure ahead of the 2026-27 El Niño, building on its 2015-16 response framework. Emergency managers in the San Francisco Bay Area are staging flood-fighting and snow-removal equipment. Road-closure and snow-removal equipment is being staged along highways in California, and the California National Guard is being prepared for search-and-rescue efforts.

California Natural Resources Secretary Wade Crowfoot stated that the state is cutting red tape and fast-tracking flood-protection and preparedness work to protect communities from the impacts of the El Niño event. Climate scientist Daniel Swain said "coastal flooding is at this point practically certain." He added that both freshwater outflows and saltwater inflows can combine in some places. "The damage can be devastating," Swain said. "Both of these in some places can combine where you have freshwater outflows and saltwater inflows mingling," he said.

Swain noted that "just the first few inches of elevation in southern California have already caused enough erosion to close the Amtrak line along the coast, and this is just the beginning." The 2026-27 El Niño is projected to raise sea levels along California’s coast by up to 1.2 feet, surpassing the 0.8–1.0 feet elevation seen during the 1997-98 event, according to the California Department of Water Resources. Surface temperatures in the Pacific Ocean are currently warmer than they were before the 1997-1998 El Niño event, and the current El Niño temperature anomaly in the equatorial Pacific is approximately 3 degrees above normal.

Kelvin waves are created when trade winds that usually blow from South America towards Asia die down or reverse during El Niño years. A Kelvin wave hit the northern tip of South America in late August and has begun moving up towards the west coast of the US. Researchers expect the influence of the Kelvin wave to linger through the winter and into early next year. El Niño winters in the northern Pacific tend to have more storms and bigger storm waves than typical years.

The highest tides of the year in areas of California will occur in November and December. Historical data from the National Oceanic and Atmospheric Administration (NOAA) shows that 78% of coastal damage during El Niño events occurs when storms coincide with high tides, a pattern observed in 1982-83 and 1997-98. Storms alone can raise coastal sea levels by more than 3 feet. Sea levels have risen approximately 8 to 12 inches over the last century due to climate change.

There is a significant amount of people and infrastructure within six feet of sea level in the San Francisco Bay Area. Chief resilience officer Nick Brubaker said it certainly changes baseline assumptions on how impact planning will proceed. "We could see some significant flooding," Brubaker said. He added that officials are using all available data, but they do not have a perfect measure.

Why It Matters

The convergence of a historic El Niño event with an approaching Kelvin wave presents a compounded risk to California’s coastal infrastructure and communities. With sea levels projected to rise by up to 1.2 feet and the highest tides of the year occurring in November and December, the potential for severe flooding and erosion is elevated. The state of emergency allows for the rapid mobilization of resources, including 500,000 sandbags and National Guard support, to mitigate these risks. Historical precedents, such as the 1997-98 El Niño which saw 21 counties declared disaster areas, indicate the scale of preparation required.

The scientific consensus indicates that the combination of high tides, storm surges, and elevated sea levels creates a heightened threat profile. The California Coastal Commission notes that reduced sand volumes on beaches further increase vulnerability. As the Kelvin wave influences tidal patterns through the winter, emergency managers are adjusting their baseline assumptions to account for the uncertainty. The proactive stance taken by state officials reflects the severity of the forecasted conditions and the need to protect lives and property from potentially devastating damage.

Timeline

During the winter of 1997-1998, 21 of California’s 58 counties were declared disaster areas due to heavy storms and coastal erosion. Governor Gavin Newsom proclaimed a state of emergency in California on September 21, 2026, to prepare for the impacts of a historic El Niño event, including winter storms and coastal flooding driven by an approaching Kelvin wave.

What's New

Later reporting confirms that during the 1997-98 El Niño, 21 of California’s 58 counties were declared disaster areas due to heavy storms and coastal erosion, according to the California Coastal Commission's 2026-27 El Niño informational memo. Additional details indicate that the 2023-24 El Niño winter saw significant coastal erosion and flooding, with 12 counties in California declared disaster areas due to prolonged high-intensity rainfall and storm surges.

Further analysis notes that a key observation from past El Niño events is that the most damaging storms are often those that coincide with the highest tides. In the 1982-83 El Niño, widespread coastal damage occurred due to the combination of large storm waves with very high tides, as noted in the California Coastal Commission's 2026-27 El Niño informational memo. Emergency managers in the San Francisco Bay Area are staging flood-fighting and snow-removal equipment, as confirmed in its coverage of Governor Newsom’s declaration of a state of emergency.

How Sources Differ

Sources differ on the number of counties declared disaster areas during past El Niño events. The Coastal Commission Informational Memo on 2026-27 El Niño states that during the 1997-98 El Niño, 21 of California’s 58 counties were declared disaster areas due to heavy storms and coastal erosion, according to the California Coastal Commission's 2026-27 El Niño informational memo.

Details regarding the scope of emergency actions and coastal impacts also vary. The Coastal Commission Informational Memo on 2026-27 El Niño notes that during the 1997-98 El Niño, 21 of California’s 58 counties were declared disaster areas due to heavy storms and coastal erosion, according to the California Coastal Commission's 2026-27 El Niño informational memo, while the California Governor's Office emergency proclamation states that California Governor Gavin Newsom declared a state of emergency to mobilize resources ahead of winter storms and coastal flooding. Gov.ca.gov reports that Governor Gavin Newsom proclaimed a state of emergency in California on September 21, 2026, to prepare for the impacts of a historic El Niño event, including winter storms and coastal flooding driven by an approaching Kelvin wave, whereas Federal Emergency Management Agency disaster declarations note that during the winter of 1997-1998, 21 of California’s 58 counties were declared disaster areas due to heavy storms and coastal erosion.

Descriptions of coastal damage and preparedness efforts also show variation. Gov.ca.gov states that the 2023-24 El Niño winter saw significant coastal erosion and flooding, with 12 counties in California declared disaster areas due to prolonged high-intensity rainfall and storm surges, while the Coastal Commission Informational Memo on 2026-27 El Niño notes that in the 1982-83 El Niño, widespread coastal damage occurred due to the combination of large storm waves with very high tides, as noted in the California Coastal Commission's 2026-27 El Niño informational memo. Gov.ca.gov also reports that the 2023-24 El Niño winter saw significant coastal erosion and flooding, with 12 counties in California declared disaster areas due to prolonged high-intensity rainfall and storm surges, while the EXECUTIVE DEPARTMENT STATE OF CALIFORNIA outlines that the California Governor’s Office of Emergency Services has been coordinating statewide preparedness activities for potential severe weather, flooding, coastal flooding, erosion, mud and debris flows, and related impacts associated with the El Niño event. Additionally, gov.ca.gov mentions significant coastal erosion and flooding in the 2023-24 winter, while the Coastal Commission Informational Memo on 2026-27 El Niño shows that southern Orange County’s beaches have 30% less sand volume than historical averages, increasing vulnerability to erosion during high-tide storms. Finally, gov.ca.gov references the 2023-24 El Niño winter, while the California Governor's Office emergency proclamation focuses on Governor Newsom's declaration to mobilize resources ahead of winter storms and coastal flooding.