It's time yet again for the king tides that visit the Bay Area and other coasts every winter, and they're coming around again this weekend, on both Friday and Saturday. This means high tides that are at least a foot and a half higher than usual — giving us all a glimpse of where the water will go as climates change and sea levels rise.
So-called king tides — which have only been so-called for about a decade — happen from December to February, but tend to peak in early January when the Sun is closest to Earth and when the moon is at perigee, also in its closest phase to earth. Around the Bay this mean high tides that rush up in spots they don't alway reach including several hours in which water often spills over the seawall along the Embarcadero, and/or bubbles up through manhole covers as in the 2017 video below.
As the Chronicle notes, surges from ferries and rainy weather tend to exaggerate these effects, and the low points along the seawall where the tides are most evident are near Piers 3 and 14. The first of these high tides will arrive around 10:30 a.m. Friday, with Saturday's possibly even higher.
Elsewhere around the Bay, these surging tides can be used to show spots of climate-change vulnerability as we face the inevitability of sea-level rise in the coming decades. "Today’s king tides are the high tides of tomorrow," as the Exploratorium's Lori Lambertson tells the Chronicle. Lambertson gives annual walking tours along the Embarcadero during king tide season, though the ocean doesn't always put on a big show.
Drivers on coastal roads, and pedestrians on coastal trails and other walkways need to beware that the water may be up where it usually isn't on Friday, Saturday, and Sunday in the morning. Low tides will be in the afternoon.
A 2012 report by the National Research Council suggested that tides around the Bay could rise as much as two feet by 2050, so the 18-inch surge predicted for this weekend isn't far off.
Below, a brief explainer about king tides from the California King Tides Project.