Bay Area sea levels expected to rise nearly 1 foot due to "planetary wave"

A slow-moving wave is travelling up the North American coast and is expected to raise water levels in the Bay Area by nearly a foot next month. But it's not going to be one giant crashing wave; in fact, people may not even notice it if they head to the coast. 

The swell moving up the coast is a planetary-scale process, meaning it's thousands of miles wide, known as a Kelvin wave, and is a direct impact of El Niño. During an El Niño event, winds shift and draw warmer ocean water from offshore and pushes it towards Central America. When the warmer water slams into the coast, it sends a coastally trapped wave, also known as a Kelvin wave, up the West Coast and towards Alaska, which can take months at a time. 

But again, it won't be one giant wave that you can see crashing at the beach. The wave is currently moving north across Central America's coast at around 6 mph. It's expected to arrive to Baja in the next week or so, Southern California by late September/early October, and the Bay Area by the first or second week of October. 

These waves can bring elevated sea levels for weeks at a time, eventually subsiding before the next wave hits. Yes, there will likely be several Kelvin waves this season. The last big El Niño in 2015-2016 featured five to six Kelvin waves, which at times coincided with atmospheric rivers that led to record high wave heights across the state.

Point Reyes and Point Sur observed the tallest waves on record in December 2015, with a 57' wave near Point Sur and over a 55' wave for Point Reyes. Mendocino recorded a nearly 64' wave and Humboldt a 60' wave, which were both their second-largest waves on record. 

Luckily, September and October tides are among the lowest of the year, so this Kelvin wave won't break records when it reaches the region in October. The bigger concern will be later this year, as California's highest king tides take place from November to January, coinciding with Thanksgiving Day and Christmas Day this year. Even without a nearby storm or ongoing Kelvin wave, near-record water levels are likely during these king tide events, which is why timing is so important. 

If the California coast sees a perfectly timed double whammy, like the king tides coinciding with an incoming storm or Kelvin wave, the potential for coastal erosion and flooding damage increases significantly. So yes, water levels off the coast of California will rise nearly a foot over the next month or so, but it's not until November and December that coastal communities really need to be alert — Make sure to prepare now before the potential of the perfect storm to hit. 

So, it's the coastal erosion and flooding from sea level rise that is almost guaranteed to happen this winter that we are concerned about. Models still are having a tough time on whether or not the Bay Area will see a super wet winter, so that's not guaranteed with El Niño, but again, high waves and more coastal erosion will be the most certain impacts.