El Niño and rising seas will flood San Francisco's Great Highway
By Daniel Okafor · Reporting from New York ·
A historic El Niño combined with chronic sea level rise puts the Bay Area at risk of severe flooding, leaving coastal communities vulnerable to an inevitable surge.
The Bay Area is not ready for the water. A historic El Niño is arriving, and it is colliding with a permanent rise in sea levels. The data shows a coastline that can no longer buffer the surge. The city will see flooding that dwarfs recent memories because the baseline has shifted.
The ocean is warming
Francisco Chavez of MBARI said the 2026-27 El Niño is one of the strongest ever. His data shows temperatures more than seven degrees centigrade over the long-term average. This warming raised the sea level by 16 centimeters.
The heat is changing the biology of the coast. MBARI researchers found tropical species like Ocyropsis in their own backyard. Bruce Robison said these sightings are indicators of a transition in deep midwater community composition.
The evidence comes from deep water. MBARI uses the M1 mooring. Instruments at 60 meters recorded temperatures of 18.18 degrees Celsius.
This is the same mechanism that drove the 1982-83 El Niño. In that event, extreme ocean warming triggered sea-level rise and coastal flooding in California. The current warming is a repeat of a physical process. We saw similar patterns during the 2015-16 El Niño. That event caused widespread sea level rise across the Pacific basin and showed how warm waters influence global weather.
Maps show the risk
Dana Brechwald of the San Francisco Bay Conservation and Development Commission warned of thermal expansion. She said the region will see about 12 inches of additional water level.
The commission developed maps to project these impacts. They show overtopping at the Oakland Airport. They show flooding in residential neighborhoods. Vulnerable areas include the Peninsula and South Bay communities such as Alviso.
This follows the trend of the 2023-24 El Niño. That cycle triggered record-breaking ocean temperatures and increased flood risks. It was the fifth-most powerful event in recorded history.
Will the coast hold?
The water is already moving. The San Francisco Chronicle reported that San Francisco recorded its highest-ever October tides during the week of Oct 29, 2026. Water spilled onto the Embarcadero near the Ferry Building on Oct 28.
Mary Ellen Carroll of the Department of Emergency Management said the National Weather Service expects water to reach the seawall by the Great Highway this winter.
Chase Davenport, director of the Ocean Beach Institute, said the current state of the coast provides a buffer. Ocean Beach is at its widest point. He said there is no real threat today.
This view relies on the current width of the sand. It ignores the coming winter storms and the rising baseline. The record October tides prove the buffer is failing.
Shannon Parkhurst of the Lemon Aide Project knows this risk. She points to houses in her neighborhood. She said, "every single one of these houses that you're seeing have been underwater." In Novato, an intersection submerged during the 1982 El Niño floods. Parkhurst said, "I want people to realize that things could be really, really bad."
The Great Highway and the low-lying shorelines of Marin and San Francisco will breach. The city is fighting a tide that has already risen. Planners now face chronic sea level rise on top of the El Niño surge. This combination pushes the high-tide baseline higher. The water will not stop at the seawall.