Weather Watch

Catching some waves this month? Here's why you might need a thicker wetsuit

Surfers experience offshore wind while surfing near Morro Bay.
Surfers experience offshore wind while surfing near Morro Bay.

The inevitable spring winds have kicked in along the Central Coast.

These relentlessly persistent winds will produce a lot of fog-free afternoons along the shore and the conditions that wind and kite surfers passionately love. But if you’re planning to head to the beach to enjoy the ocean, you may want to bring a thicker wetsuit, and here’s why.

Last Thursday, the northwesterly winds reached 53 mph at the Diablo Canyon Power Plant’s meteorological tower. As the northwesterly winds blow parallel to our coastline, the friction of the wind causes ocean surface water to move. Because of the Coriolis Effect, the surface water flows to the right, or offshore. This, in turn, causes upwelling along the coast as cold, clear and nutrient-rich water rises from the ocean’s depths to the surface along the immediate shoreline to replace the shallow water that is pushed out to sea.

On days with plenty of sunshine and lots of upwelling, California giant kelp (Macrocystis) can grow up to 24 inches in just one day, ultimately reaching more than 150 feet in length. At that rate, you could almost see this type of algae grow right in front of your eyes. Usually, the peak growing season for giant kelp occurs in spring during the height of the upwelling season.

So far, seawater temperature this April has averaged a chilly 52 degrees at the Diablo Canyon Power Plant. The coldest seawater temperatures of the year usually occur in April through May and can reach a bone-chilling 47 degrees. As of Saturday morning, seawater temperatures ranged between 49 and 50 degrees.

Since 1976, PG&E and Tenera Environmental Services scientists from Diablo Canyon Power Plant have measured seawater temperatures along the rugged cliffs and coastal terraces of the Pecho Coast, which stretches from Montaña de Oro State Park south to the Point San Luis Lighthouse.

Numerous watertight, electronic oceanographic recorders about the size of a hot dog keep track of the seawater temperatures. They are exchanged, downloaded and calibrated on a continuous basis. Over the decades, various marine biologists have journeyed to the tide pools at minus low tides along the Pecho Coast and exchanged these recorders that measure seawater temperatures. If the conditions are right at night, bioluminescence from plankton blooms and/or the deep scattering layer can mark their track across the cool, wet and slippery rocks of the littoral. Millions of seawater temperatures have been recorded along the stretch of coastline since 1976 with a yearly average of 52.2 degrees.

Based on monthly averages, the coldest seawater temperatures along the Central Coast occur at this time of year, when the northwesterly winds blow the hardest. The coldest month on record was April 2008, which averaged a bone-chilling 49 degrees. That month saw some of the most consistently strong northwesterly winds that we have ever seen.

Historically, the warmest months of the year occur from September through November, as we have a relaxation of the northwesterly winds.

The warmest hourly seawater temperature on record along the Pecho Coast near the intertidal zone occurred in October 2015, which saw a seawater temperature reading that reached 67.5 degrees. At that time, we were in the middle of one of the strongest El Niño events (warmer-than- normal seawater temperatures) ever recorded. The other warmest seawater temperature readings occurred in September 1983 at 66.7 and October 1997 at 66.2; both of these readings also occurred during strong El Niño events.

Marine biologist Scott Kimura, who has swapped out countless temperature recorders over the decades and has surveyed the intertidal “tide pools” along the Pecho Coast since 1976, closely tracks the tides. He pointed out that starting Monday the Central Coast will see nearly 21 straight days of negative low tides — a rare occurrence indeed.

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Join PG&E employees April 21 to celebrate Earth Day at Montaña de Oro State Park. The event is one of a number of service projects sponsored by PG&E and the California State Parks Foundation. Be sure to dress for outdoor work with long pants, long-sleeved shirt, sturdy shoes, hat, gloves and sunscreen.

Snacks and a light lunch will be provided. Bring your own refillable water bottle. Rangers will provide tools and supervision. Please register at the California State Parks website: .

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 or follow him on Twitter: @PGE_John.
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