Weather Watch

Two super moons and King Tide will ring in 2018. It all starts with the Wolf Moon

'King tides' cause dramatic sea level shifts in SLO County

A period of “king tides” brought dramatic shifts in sea level to San Luis Obispo County, California, on Monday, December 4, 2017.
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A period of “king tides” brought dramatic shifts in sea level to San Luis Obispo County, California, on Monday, December 4, 2017.

The only super moon event for all of 2017 occurred earlier this month. This January, however, will see two super-moon occurrences.

The first one, nicknamed the Wolf Moon, will happen New Year’s Day night, which will bid a fond farewell to 2017. That will be followed by another super moon on Jan. 31, a rare red and blue moon combination thanks to a partial lunar eclipse. A Blue Moon is the second full moon of the month. A red, blood or copper moon is the color of the moon during a lunar eclipse.

All these colored moons of January correspond to the highest tides of 2018. In fact, we won’t see predicted tides this high until December 2020.

In early December, I wrote about the 2017 King Tide that occurred Dec. 4 when the sea reached 6.8 feet at the Port San Luis tide gauge. On New Year’s Day and again on Tuesday, the King Tides will be even higher than December’s high tide or late January’s expected tides, and here’s why.

Unlike the King Tides of early December and late January, the Earth will be at Perihelion, when we reach our closest point to the sun, for all of 2018 on Jan. 2. Perihelion occurs during winter in the Northern Hemisphere and summer in the Southern. Aphelion is when Earth is farthest from the sun.

You see, our planet’s orbit around the sun is an ellipse, a shape that can be thought of as a “stretched out” circle or oval. Not only is the Earth’s orbit around the sun an oval, but so is the moon’s orbit around the globe. The moon is about 30,000 miles closer to Earth at perigee than apogee.

The time between New Year’s Day and Tuesday, the sun, moon and Earth will line up in what is known as syzygy. But the moon will also be at perigee; and when this happens, astronomers called it perigee-syzygy! The gravitational forces exerted by the moon and sun create the timeless tides. These “tidal forces” are not the total gravitational forces exerted by the sun and moon on Earth, but the difference between these gravitational forces over the surface of the planet.

If you missed Sunday’s supermoon, you still have a chance on Jan. 1 and a third time on Jan. 31, 2018. NASA released a video explaining just what is a supermoon.

On New Year’s Day, the predicted tide will reach 6.9 feet at 8:29 a.m., followed by a low tide of -1.7 feet at 3:47 p.m. at the Port San Luis tide gauge. In other words, the level of the sea will shift 8.6 feet in a little over seven hours, followed by another 6.9 high tide at 9:16 a.m. Tuesday and a low tide of -1.7 4:35 p.m. later that day. These flood and ebb tides will create ripping currents in California’s bays and estuaries.

The predicted high tides could be higher than expected New Year’s Day and especially Tuesday. Seawater temperatures are warmer than typical for this time of the year. When the water warms, it causes thermal expansion in the upper levels of the ocean. Consequently, seawater levels can be several inches higher than those predicted in the tide tables.

Also, a vigorous upper-level low-pressure system off our coastline will produce increasing southerly winds and decreasing atmospheric pressure. Lower atmospheric pressure can create higher sea levels. The southerly winds can produce storm surge along our shores. All these factors together: warmer seawater, southerly winds and low pressure could yield even higher water levels. To view the real-time Port San Luis tide and sea-level data, visit portsanluis.com.

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PG&E’s commitment to clean energy took a big step forward in 2017. To learn more, please visit pgecurrents.com.

John Lindsey’s column is special to The Tribune. He is PG&E’s Diablo Canyon marine meteorologist and a media relations representative. Email him at pgeweather@pge.com or follow him on Twitter: @PGE_John.

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