A Kelvin wave headed towards California is about to lift the ocean along the West Coast by up to a foot, and it could hold it there for months. Nobody on the beach will see it arrive. This week's headlines called it a "thousand-mile wave set to smash into the coast," which left a lot of ocean lovers stuck between panic and an eye roll. Marine biologist Andrew Lewin slows the story down and explains what is coming. A Kelvin wave is a slow bulge of warm water that moves below the surface, and this one was launched by an El Niño that NOAA gives a 75% chance of becoming the strongest since records began in 1950.
Andrew walks through how El Niño works in the tropical Pacific, how a burst of westerly wind sends a Kelvin wave east along the equator at about 250 kilometres a day, and how it splits at South America and hugs the coast north toward California, Oregon, Washington, British Columbia and Alaska. The danger comes from stacking. Storms and tides start from wherever sea level happens to be, so an extra foot of water lets an ordinary winter storm at high tide do the damage of a much bigger one. California's highest tides arrive in November and December, and the biggest storms follow from January to March. Southern California has already had a taste: surf from Hurricane Marie topped the coastal rail tracks in San Clemente in September and closed the line. Marin County is handing out sandbags, and the 1997-98 El Niño left 21 of California's 58 counties declared disaster areas.
Andrew also covers the ocean life most of the coverage skips. A Kelvin wave can slow phytoplankton growth at the base of the food web, and it's arriving on a coast already under a marine heatwave, with kelp forests under pressure, starving seabirds and warm-water species moving north. NOAA projects 10 to 12 inches of permanent sea level rise along US coastlines between 2020 and 2050, so this winter gives California a preview of the baseline it's heading toward. You'll leave with three questions to ask about any scary wave headline and practical steps for anyone who lives on a coast. Join Andrew live on Ocean Decoded Live, Monday to Thursday at 5 PM Eastern.
Chapters:
0:00 - A Wave Moving Up the Coast
2:16 - Floods, Droughts and a Wetter California
4:34 - "Rolling the Dice"
6:49 - What's Different This Time
8:21 - How Fast We Stop Heating the Ocean
Takeaways:
A Kelvin wave is a slow, low bulge of warm water that travels below the surface. It can raise sea level along the California coast by up to a foot for months.
It starts when westerly winds in the far western Pacific push warm water east. The pulse crosses the Pacific along the equator at about 250 km a day, taking two to three months.
At South America the wave splits, and part of it runs north along the coast past Mexico, California, Oregon, Washington and British Columbia toward Alaska.
It's only a few centimetres high at the surface, but it pushes the boundary between warm and cold water down by tens of metres.
NOAA gives this El Niño more than a 90% chance of being very strong this fall and winter, and a 75% chance of becoming the strongest since 1950.
An extra foot of water raises the starting line for every storm and tide. California's highest tides come in November and December, and its biggest storms come from January to March.
High surf from Hurricane Marie on top of high tides topped the coastal rail tracks in San Clemente on September 8 and closed the line. Marin County is already preparing with sandbags and flood barriers.
Kelvin waves can slow phytoplankton growth, and this one is hitting a coast already stressed by a marine heatwave since May 2025.
Environment and Climate Change Canada warns this El Niño could bring higher sea levels, storm surge, erosion and marine heatwaves to BC. No BC-specific number for this wave has been published yet.
NOAA projects 10 to 12 inches of sea level rise along US coastlines between 2020 and 2050, so this winter's temporary foot of water previews the permanent baseline coming in about 25 years.
Before trusting a scary wave headline, ask three questions: How much water? For how long? What is it stacking on top of?
If you live on a coast, look up your king tide dates and flood maps, sign up for emergency alerts, join a King Tides Project photo day, and push your community to plan for higher baselines now.
#OceanConservation #MarineBiology #SaveOurOceans #ProtectTheOcean #OceanAwareness #BluePlanet #ConservationMatters #ScienceForChange #SustainableOceans
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