Weather Watch

King tides to bring extra-high tides to Central Coast

Los Osos boater Paul Irving at high tide at the Baywood Park Pier, in Morro Bay.
Los Osos boater Paul Irving at high tide at the Baywood Park Pier, in Morro Bay. John Lindsey

The next few days will see the phenomenon of “king tides” along the California coast.

“King tides” refers to tides that are the highest and lowest of the year that are usually separated by less than 12 hours. The term originated in Australia and has since spread throughout the rest of the nations that border the Pacific Ocean.

These high tides will occur this Tuesday, Wednesday and Thursday. The highest will happen Wednesday morning at 8:27 a.m. when the tide will reach 6.7 feet.

However, it may be higher than predicted — and here’s why:

Currently, one of the strongest El Niño events on record is brewing in the Pacific, and combined with global warming, it has contributed to some of the warmest fall seawater temperatures ever recorded. Usually, seawater temperatures along the Central Coast average around 58 degrees during the month of November. So far this November, the temperature average is 62 degrees.

When the water warms, it causes thermal expansion in the upper levels of the ocean. Consequently, seawater levels can actually be several inches higher than those predicted in the tide tables. In fact, the observed water level has been about 6 inches higher than predicated tides at the Port San Luis Tide Gauge. In other words, if the tide tables predict a 6.7-foot high tide, Wednesday’s actual tide would be above 7 feet. High indeed!

The maximum tidal range along the Central Coast can reach from more than 2 feet below the mean low-water mark to more than 7 feet above it, for a tidal range of more than 9 feet. The greatest tidal range that I know of is in the Bay of Fundy on the east coast of Canada, which can exceed 52 feet.

The tides are caused by the gravitational forces exerted by the moon and sun. The bottom topography — or underwater bathymetry of our coastline — also plays an important part in the changing tides.

This tugging produces a tidal “bulge,” or area of higher sea level on the ocean’s surface. As Earth rotates eastward on its axis, the Central Coast moves into this bulge, which produces a flood tide, and eventually a high tide. As Earth continues to spin, we move into an area of below-normal sea level, or nodes, which produce an ebb tide, eventually reaching low tide. The slack tide is when the tide is not coming in or going out.

The California King Tides Initiative is encouraging the public to document these tides that occur along the state’s coast. The organization’s goal is to document changes to our shoreline and give the public a glimpse of the future. If you’re going to photograph these tides, please be safe! Never turn your back to the ocean, and always be aware of your surroundings and of weather and oceanographic conditions.

John Lindsey is the PG&E Diablo Canyon meteorologist and media relations representative. Email him at pgeweather@pge.com

Did you know that PG&E delivers to its customers some of the nation’s cleanest electricity? More than 55 percent of the power comes from sources that emit no greenhouse gases, including Diablo Canyon Power Plant. To learn more, please visit www.pge.com.

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