The gravitational forces exerted by the moon and the sun create the timeless tides. This towing produces a tidal “bulge” or area of higher sea level on the surface of the ocean.
As the Earth spins east on its axis, California moves into this bulge, producing a rising tide, and eventually a high tide. As the Earth continues to rotate, we move into an area of lower than normal sea level, or knots, which produces an ebb tide, eventually reaching low tide. The slack tide is when the sea does not come in or go out. Typically we experienced both low and high tides per day.
Starting Dec. 2 and running through Dec. 5, California will see the phenomenon of “royal tides” along the coast. These tides are among the highest and lowest of the year, separated by less than 12 hours. The term originated in Australia and has since spread to the rest of the nations that border the Pacific Ocean.
The high will occur at 9:30 a.m. on December 4, when the predicted tide reaches 6.8 feet. This will be followed by a low tide of -1.5 feet at 4:46 p.m. later today. In other words, sea level will move 8.3 feet in just over seven hours. These rising and falling tides will create rip currents in California’s bays and estuaries. The maximum tidal range along the central coast can range from over 2 feet below the mean low water mark to over 7 feet above it, for a tidal range of over 9 feet.
However, actual tides may be higher or lower than expected, and here’s why:
In 2015, one of the strongest El Niño events on record was brewing in the Pacific. Combined with global warming, it has contributed to some of the hottest seawater temperatures on record. Usually the sea water temperature along the central coast averages around 58 degrees in November. But that month in 2015, the average temperature was nearly 62 degrees.
As water warms, it causes thermal expansion in the upper levels of the ocean. As a result, sea water levels can be several centimeters higher than predicted in tide tables. In fact, the water level observed that month was about 6 inches higher than the tides predicted at the Port San Luis tide gauge. In other words, if the tide tables predicted a high tide of 6.7 feet on November 25, 2015, the actual tide was 7.2 feet.
Other factors like storm surges when winds blow over the ocean surface towards the shoreline can increase the tides. If the winds are strong enough, they can push and accumulate water on beaches and raise sea levels by several feet – or several feet below if the winds are blowing seaward.
Another factor is atmospheric pressure. In January of this year, atmospheric pressure readings reached 1,033.9 mb, or 30.53 inches of mercury (inHg), at the San Luis Obispo County Regional Airport and 1,035.6 mb (30. 58 inHg) at Paso Robles Airport. These readings were some of the highest I have ever seen.
The above-average weight of the atmosphere produced lower-than-expected tide levels; the higher pressure pushed down the surface of the water. On January 27, the predicted tide level was -0.7 feet, but due to higher pressure, the actual level was -1.1 feet.
Lower atmospheric pressure, for example during storms, can produce higher sea levels. Additionally, storm runoff from flooded streams and rivers flowing into estuaries and bays and waves generated by high winds can also create higher than expected sea levels.
A storm event can combine all of these factors: “king tides”, warmer sea water, storm surge, low pressure and storm runoff combined with a high swell can produce much higher water levels. higher than expected.
More worryingly, climate change will appear at an increasingly rapid rate.
“Global warming is causing actual tides to be higher than predicted on tide charts, as warming waters and melting ice caps in Greenland and Antarctica raise sea levels across the planet,” he said. Josh Willis, NASA oceanographer and climatologist.
Early this decade, PG&E assembled a team of atmospheric scientists, oceanographers and meteorologists. Their consensus is that sea levels will rise about 7 inches along the California coast by 2030 and almost a foot by 2040.
To get an idea of what it will look like in the not-too-distant future, the California King Tides Initiative encourages the public to document these tides that occur along the state’s coastline. The organization’s goal is to document changes to our coastline and give the public a glimpse of what’s to come. If you are going to photograph these tides, be careful. Never turn your back on the ocean and always be aware of your surroundings, weather and oceanographic conditions.
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This story was originally published November 25, 2017 1:01 p.m.