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The Tides Have . . . Turned?

Cameron Tuttle, the former race chair at Tiburon Yacht Club and Latitude 38 reader, has a question. He saw a Facebook post from Bay Area PRO guru Jeff Zarwell, who described the rigors of running the Nations Cup Grand Final during some bizarre tides.

“The Nations Cup . . . a world championship in match racing with 19 teams, match after match after match,” Zarwell wrote on Monday. “I have no idea how many matches we actually got off, but when you figure racing started at 10 each morning, and didn’t stop until 6 in the evening, that alone sounds like a lot.”

J/22s match racing
A semifinals match-up during the World Sailing Nations Cup last Saturday, hosted by St. Francis Yacht Club in J/22s.
© 2019 Amanda Witherell

“To make it even more challenging,” Zarwell continued, “a normal tide cycle is a little over six hours. Because of rain runoff and dams like Oroville releasing over a billion gallons of water, we actually had tidal changes every two hours, causing us to have to stop and completely re-set the race course every couple of hours. It was the most challenging course to manage that I have ever encountered.”

Tides table graph
The tide tables from last weekend don’t tell the full story of what was going on in the Bay.

Tuttle said that he had been observing some aberrant tides.

“I’ve been noticing that the tides aren’t exactly as predicted lately,” Tuttle wrote us, “and did attribute it to the runoff, but I can’t quite get my head around the physics and hydraulics that result in such a dramatic a change in periodicity of the tides. I’m wondering if anyone else out there in Latitude Nation has also observed what Jeff is speaking to, and if someone can offer a technical explanation.”

We are calling on Kame Richards, Max Ebb (and, like, Lee Helm) and any hydrometeorology aficionados for some answers. Please write us here, or comment below.


  1. Tim Dick 5 years ago

    I suspect part of the issue is water temperatures: record volumes of cold snow-melt water rocketing down the Sacramento River 24×7 may tend to flow underneath incoming tides of ~54F ocean water at the Angel Island area. This may steer incoming tides south around Treasure Island causing a back-eddy near the Berkeley Circle. Just speculation… Lee Helm will indeed have the answer!

  2. Beni Bacon 5 years ago

    Back around the start of April, I was out catching what I had hoped was the last two hours of current up the Sacramento towards Rio Vista. Nope tide/current was already outgoing. I spent two days anchored off Decker Island and noticed that the outgoing tide was more around 9 hours long, instead of the expected 6 ish. That did help going back down stream.

  3. Mark Harvey 5 years ago

    According to NOAA and the SF Tide gauge the actual tides lined up with the predicted, however, the highs were higher and the lows were also higher.

  4. Bruce H Munro 5 years ago

    The stronger than normal flow from the Sacramento River system caused a huge back eddy along the city front from Fort Point to Fort Mason. It was flood tide on the city front when the tide tables said it should be ebb. It was very weird but also very real.

  5. Ursus 5 years ago

    Warm seawater is still denser than cold freshwater, so the river water will initially stay on top.
    But when the two start mixing, interesting things happen, especially vertically.

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