A pulse of warm water hitting the Pacific coast could mean erosion and flooding

SEATTLE (AP) — Sea levels along the West Coast will begin to rise by up to a foot this month as a series of pulses of warm water called Kelvin waves hit the shoreline and move north, sparking concerns about beach erosion and flooding in areas already impacted by climate change and El Niño. Kelvin waves are not like tsunamis, and they don’t curl over and crash on the beach. A better image is water sloshing in the bathtub or a swimming pool during an earthquake.

In the ocean, they are bulges of water that lift the sea level as they move along the coast. They’re common during El Niño events, but this year’s super El Niño could intensify the impacts, experts say. Over the next week, the 6-inch to foot-tall surge will move north along the California coast at about 6 miles per hour (9.6 kilometers per hour), or 150 miles per day (241 kilometers per day), bringing higher sea levels to Oregon and Washington state.

Experts predict the waves will continue to pass through from October until February. “It’s not that this Kelvin wave is going to come and flood anything on its own,” said Michael Jacox, a research oceanographer with National Oceanic and Atmospheric Administration Fisheries’ Ecosystem Science Division. If you start with sea levels that are 6 inches higher than normal, when you have really high tides, big storms or storm surges, the water levels are now 6 inches higher, he said.

“The effects can be amplified,” he said. The waves also increase ocean temperatures and push cold, nutrient-rich waters deeper below the surface, which has an impact on marine life. Here’s what to know about Kelvin waves.

Kelvin waves are a “fact of life” during an El Niño, a naturally occurring climate pattern involving the warming ocean waters, said Dillon Amaya, an assistant professor in the Department of Marine, Earth, and Atmospheric Sciences at North Carolina State University. They form when the trade winds along the equator change direction. Winds blowing east to west along the equator push water in the Pacific Ocean west toward Asia, Jacox said.

When those winds weaken or reverse direction, that bulge of water gets pushed back toward the east along the equator until it hits South America. When the surge of water hits the coastline at the equator, it moves north and south along the North and South American coasts. “The effects can be amplified,” he said.The waves also increase ocean temperatures and push cold, nutrient-rich waters deeper below the surface, which has an impact on marine life.Here's what to know about Kelvin waves.How does a Kelvin wave form?Kelvin waves are a “fact of life” during an El Niño, a naturally occurring climate pattern involving the warming ocean waters, said Dillon Amaya, an assistant professor in the Department of Marine, Earth, and Atmospheric Sciences at North Carolina State University.They form when the trade winds along the equator change direction.Winds blowing east to west along the equator push water in the Pacific Ocean west toward Asia, Jacox said.