By Amy Graff, SFGATE
Published 9:25 am PST, Thursday, December 20, 2018
Bob Siegel walks with his bicycle through water from the bay spilling onto the sidewalk at Pier 14 along the Embarcadero during high tide in San Francisco, Calif. on Tuesday, Nov. 24, 2015. King tide conditions are causing higher than usual water levels. lessBob Siegel walks with his bicycle through water from the bay spilling onto the sidewalk at Pier 14 along the Embarcadero during high tide in San Francisco, Calif. on Tuesday, Nov. 24, 2015. King tide conditions … more
Photo: Paul Chinn, The Chronicle
Photo: Paul Chinn, The Chronicle
It’s the time of year when the sun and moon reach their closest point to Earth, aligning the celestial bodies like a perfect cue shot to create maximum gravitation pull.
The resulting surge of the ocean’s waters, often referred to by the non-scientific term “king tides,” usually occurs in December and January. They’re in the forecast for the Bay Area across the next five days.
The highest will happen at 10:20 a.m. on Saturday and again at 11:05 a.m. on Sunday, when the predicted tides will reach 6.9 feet. That will be accompanied by a low tide of -1.3 feet at 4:50 p.m. later that day on Saturday and -1.49 on Sunday. In other words, the level of the sea will shift some eight feet in a little over seven hours each day.
While the National Oceanic and Atmospheric Administration predicts tides over six feet through Dec. 26, Brian Garcia, a meteorologist with the National Weather Service, says other environmental factors could raise them even higher, potentially causing minor flooding in low-lying coastal areas.
“Predicting tides is really easy as they’ve tracked them for so long and the mathematics can tell you exactly how much the water is going to rise,” says Garcia. “Where it differs, year to year, are tidal anomalies. Those tidal anomalies are anything that makes the water level higher or lower than predicted.”
In coming days, one anomaly that could exacerbate the tides is above-normal water temperatures. In December, Northern California temperature readers for Pacific Ocean are usually in the mid-50s, but in recent weeks they’ve been in the high-50s and even brushing with 60 degrees in Monterey Bay. Warmer waters can cause thermal expansion, leading ocean waters to rise a couple inches above tidal tables.
Another factor is a moderate swell. Fifteen-foot waves off Northern California’s shores could push and pile the water up even farther onto beaches.
How much higher the tides will rise due to the warmer waters and swell is still under discussion.
“Currently, with this last high-tide we had today, the forecasted high was somewhere at 6.5 feet, but the actual observation at the S.F. station today at 8:54 a.m. was 6.8 feet. We had a .3 foot anomaly today,” Garcia said. “If conditions are looking similar tomorrow, it’s going to put us up to a potentially seven-foot tide, which means we’re well within range to see impacts in places like Bayside Marin and Embarcadero.”
Garcia says an issue that occurs when the Embarcadero floods is people drive into work and park in a lot when the tide is out. If they return to their car in the afternoon, they might find it partially under water.
A weak storm system is headed for the Bay Area Thursday and again Sunday and Monday, but Garcia says these likely won’t have an impact.
“Right now, it doesn’t look like the storms are going to play a significant role in the exacerbation of the king tides,” he said. “Winds won’t be set up right.”