The super El Niño has set off a powerful ocean wave that is advancing up the Pacific coast, and it will arrive in California soon. There it could elevate sea levels by up to a foot for months on end. Scientists warn that the wave will make the winter storms already anticipated this year much more perilous.
The wave and how it forms
These vast swells span thousands of miles and balance Earth’s rotation. During El Niño years, they act in a distinct way. They set off oscillations in the boundary between warm, light surface water and cold, dense bottom layers, making that border rise and fall within about 330 feet. That’s why these El Niño-driven waves are called internal Kelvin waves.
When shifts happen in the winds near the equator over the far western Pacific, they ease the constant winds blowing from South America toward Asia. Then warm water and higher sea levels move slowly eastward.
How the wave travels
After an internal Kelvin wave begins, scientists can follow its course along the equator and forecast the moment it reaches the South American shoreline. That is as far east as the wave travels. From there, it divides into two branches, referred to as coastal trapped waves, which extend north and south across thousands of miles at a pace of roughly 6 mph.
According to David Webb, a physical oceanographer at the National Oceanography Centre in the U.K., all nations and territories that border the eastern Pacific Ocean share the same risk.
The tide distortion
In California and elsewhere, the wave adds to the regular tides, regardless of whether El Niño brings storms. “What is most likely to be seen is a period, or maybe a few weeks, when the normal [pattern] of tides and tidal currents is distorted, with both high and low tides being higher than normal,” Webb said. Tides could rise by “tens of centimeters,” or about a foot.
Higher tides make storms more dangerous. “A key observation from past El Niño events is that the most damaging storms are often those that coincide with the highest tides,” Kate Huckelbridge, executive director of the California Coastal Commission, wrote in a Sept. 11 memo sent to warn coastal homeowners and residents to prepare for extreme conditions, including flooding.
The stakes this winter
Experts say storms can push coastal waters up by over 3 feet on their own. Climate change has already pushed sea levels up by at least 8 inches. Gov. Gavin Newsom of California declared a state of emergency last week, allowing the state to prepare equipment and resources ahead of expected storms, according to a report from The Guardian published Monday (Sept. 28).
The harm caused by a storm grows much worse when it reaches its peak at high tide rather than low tide.
What happens next
During an El Niño event, several internal Kelvin waves may appear inside it, and the biggest ones tend to show up during the winter. Webb expressed doubt that there will be more than one full wave this time.
| Wave type | Behavior |
|---|---|
| General Kelvin wave | Balances Earth’s rotation over thousands of miles |
| Internal Kelvin wave | Causes boundary oscillation within about 330 feet |
| Coastal trapped wave | Spreads north and south from the equator |
| Event | Timing |
|---|---|
| Wave generation | Triggered by changes in equatorial winds |
| Wave arrival | Predicted to hit California soon |
| Storm season | Expected this winter |
| Emergency declaration | Issued last week by Gov. Newsom |
Preparing for the coast
For months, the swell will remain above the tides. Each high tide will rise higher than usual, while every low tide will come nearer to sea level than normal.
During that period, a major storm’s impact combines with the wave’s force, producing an effect greater than either cause acting on its own. That wave does not halt at California’s coastline. It travels north and south across the whole eastern Pacific coast, placing every coastal settlement at risk, though at different moments.
Webb expresses doubt that there will be more than one full wave this time, which provides some consolation. Still, a single large wave carries sufficient force to alter the shape of the coast for months.
Huckelbridge’s warning urges preparation before the storm arrives, since the ocean is already in motion.
Source material: “Powerful 'Kelvin wave' triggered by super El Niño threatens to raise sea levels off the California coast for months,” Live Science.
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