Subsurface Kelvin wave set to raise California sea levels by 30 centimetres

Mechanics of the subsurface wave

An underwater oceanic disturbance known as a Kelvin wave is traveling northward along the Pacific coastline and will cause sea levels in California to rise by up to 30 centimetres. Unlike standard ocean waves, a Kelvin wave is invisible to the naked eye and cannot be surfed, functioning instead as a subsurface pulsation of warm water across thousands of kilometres. The process begins in the western equatorial Pacific when easterly trade winds weaken. Under normal conditions, these winds exert steady pressure on surface waters, keeping a large volume of warm water pooled near Indonesia. When the winds ease for an extended period, that warm water shifts eastward across the Pacific to South America, where the equatorial wave splits into two coastal waves heading north and south. A coastal wave of this type can travel up to 25,000 kilometres along continental margins.

Projected path along the Pacific coast

On 2 October 2026, the northbound wave was located north of Cabo in the Gulf of California, moving at a speed of approximately 10 kilometres per hour. The warm water mass will reach San Diego next week before advancing toward San Francisco Bay in early October. After passing Central and Northern California, the wave will continue its northward trajectory along the North American coastline toward Alaska. The elevated sea level conditions resulting from this subsurface wave are expected to persist along the California shoreline for several months.

Coastal flood and erosion risks

The temporary 30-centimetre sea level increase creates severe vulnerabilities when it aligns with astronomical high tides, strong ocean swells, and storms. Dillon Amaya, an oceanographer at North Carolina State University, explained that each incremental water rise of 5–10 centimetres practically doubles the probability of coastal flooding. Portions of Southern California have already experienced heavy storms in recent weeks, leaving beaches and coastal infrastructure exposed to erosion. The convergence of elevated baseline sea levels and regular tidal cycles means that even moderate coastal weather events can produce severe shoreline flooding and structural damage.

The Kelvin wave is both a cause and a symptom of El Niño.

Interaction with El Niño cycles

As the coastal wave travels north, the deep pool of warm water suppresses the normal upwelling of cold, nutrient-dense water from ocean depths to the surface. Michael Jacox, a researcher at the National Oceanic and Atmospheric Administration (NOAA), noted that coastal waves simultaneously elevate sea level and water temperatures while driving colder nutrient layers deeper underwater. This dynamic reinforces El Niño, a recurring climate pattern that appears every two to seven years and brings droughts, floods, and extreme temperatures across the globe. By trapping warm water along the coastline, the Kelvin wave alters local marine habitats and sustains atmospheric changes over extended periods.

These Kelvin waves are therefore, in many ways, the engine of El Niño. They contribute to its development and maturation over the months.