Super El Niño Kelvin Wave Poses Months-Long Sea Level Threat to California

A potent ‘Kelvin wave’ unleashed by this year’s super El Niño is progressing northward along the Pacific coast of Central and North America, posing a significant threat to California’s shoreline. Researchers warn that this phenomenon could elevate sea levels by as much as one foot (30 centimeters) for an extended period, amplifying risks associated with severe storms, flooding, and coastal erosion during the upcoming winter season.

While Kelvin waves are recognized planetary-scale oceanic events, experts express concern because these specific waves will likely exacerbate the damage caused by the record-breaking El Niño. David Webb, a physical oceanographer at the U.K.’s National Oceanography Centre, explained that while typical Kelvin waves balance Earth’s rotation, the waves generated during El Niño years are distinct. They are classified as internal Kelvin waves because they cause oscillations in both ocean surface height and internal boundaries, specifically moving the border between warm surface water and cold, dense bottom layers up and down by approximately 330 feet (100 meters).

These internal waves are initiated by shifts in surface winds across the equator in the far-western Pacific. Westerly wind bursts weaken the standard trade winds that usually blow from South America toward Asia, allowing warm water and elevated sea states to slowly slosh eastward. Webb noted that the generation process may involve complex wind changes at various locations and times, potentially resulting in a less structured wave pattern.

Once activated, researchers can monitor the wave’s trajectory along the equator to predict its arrival at the South American coastline. Since the wave cannot proceed further east, it divides into two coastal trapped branches that travel north and south for thousands of miles at roughly 6 mph (10 km/h). This vulnerability extends beyond California to all regions bordering the eastern Pacific Ocean.

In California, the internal Kelvin wave’s impact will叠加 with existing tidal patterns, independent of any storm activity sparked by the El Niño. Webb predicted a period of several weeks where normal tidal cycles would be distorted, resulting in both high and low tides being significantly higher than usual, with rises of tens of centimeters.

Kate Huckelbridge, executive director of the California Coastal Commission, highlighted in a Sept. 11 memo that higher tides magnify the effects of storms, which are more frequent in certain U.S. areas during El Niño conditions. The memo urged coastal residents and homeowners to prepare for extreme weather, including flooding. Huckelbridge emphasized that past El Niño events show the most destructive storms often coincide with peak tides, making them far more damaging than if they occurred during low tide.

Webb also pointed out that storms alone can raise coastal sea levels by more than 3 feet (1 meter). When combined with the at least 8 inches (20 cm) of sea level rise already attributed to climate change, the potential for damage is substantial. In response to forecasts, California Governor Gavin Newsom declared a state of emergency last week to mobilize resources and equipment before potential storm strikes, according to The Guardian.

Although multiple internal Kelvin waves can occur within a single El Niño cycle, with the largest typically recorded in winter, Webb doubts that more than one full wave will materialize during this event.