Large underwater pulses called Kelvin waves are adding to sea level rise on the Washington coast. They are associated with the very strong El Niño underway. And depending on the intensity of the weather from that climate pattern, the waves could significantly impact the Washington coast this winter.
El Niño and its counterpart, La Niña, are naturally occurring climate patterns that originate near the equator in the tropical Pacific Ocean, depending on sea surface temperatures that result from the direction and intensity of trade winds. El Niño forms when the ocean surface warms to above-average temperatures; La Niña forms when the surface waters cool.
This year's El Niño weather pattern is stronger than any seen since record keeping began 75 years ago. It is expected to bring extremely warm air temperatures to the Pacific Northwest this winter, along with the potential for drier weather.
"We're expecting warmer waters off our coast as well," Deputy State Climatologist Karin Bumbaco said.
Much of that heat is carried by the Kelvin waves. While they do not appear on the surface and never break, they can push sea levels higher. Kelvin waves are a normal underwater feature of any El Niño. But the warmer the water, the more it expands. Bumbaco said this year's pattern could make any seasonal flooding worse, especially with high tides or storms.
"If you see flooding regularly in winter, it would likely be more frequent this winter," she said. "It's tilting the odds towards seeing more of that coastal flooding."
George Kaminsky, a coastal engineer from the state Department of Ecology, said those effects can be quite extreme. Kaminsky keeps a close eye on shoreline erosion. He said these Kelvin waves can cause extremely rapid sea level rise.
"Rather than a few millimeters a year, we're getting a foot within a few weeks. So it can be really interesting and can be really scary," he said.
Kaminsky said bigger waves, stronger wind and more intense storms can add up to sea levels that are 2 to 3 feet higher. And the Kelvin waves were already apparent in May, June and July this year. The biggest effects are expected during the highest tides in the fall and winter, especially the King Tides in December. He said those events could test some new nature-based solutions the state has implemented to help with shoreline erosion in some areas.
Coastal cities including Stanwood, Aberdeen, Hoquiam and Tahola on the Quinault Indian Reservation, and parts of Seattle's South Park along the Duwamish River are preparing for high water with emergency repairs to levees and sandbagging.
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This story comes to you from the Northwest News Network, a collaboration between public media organizations in Oregon and Washington.
