Weather Watch

Strong spring winds make ocean waters especially cold each May

Strong winds buffet the trees and flags in the Baywood neighborhood of Los Osos on Saturday.
Strong winds buffet the trees and flags in the Baywood neighborhood of Los Osos on Saturday.

Whether you are a scuba diver, surfer, fisher or just a beach visitor, you undoubtedly have noticed the frigid seawater temperatures along our rocky coast.

The gale force northwesterly winds that have blown along much of California’s coastline this May have produced the coldest seawater temperatures of the year. In fact, they reached a bone-chilling 49 degrees Fahrenheit at PG&E’s Diablo Canyon Power Plant on Friday night.

On Saturday, northwesterly winds peaked at 46.2 mph with gusts at 62 mph at 6:45 p.m. Windy indeed! This is the strongest northwesterly events this year and one of the strongest of all time.

So why do these winds generate such cold ocean temperatures? As the northwesterly winds blow parallel to our coastline, the friction of the wind causes ocean surface water to move like a gigantic hand that sweeps across the ocean’s surface. Combined with the rotation of the earth, the surface water moves to the right of the wind direction, thus out to sea.

This creates a void along the shoreline and cold and nutrient-rich water is drawn from below to fill it. The upward movement of this colder water is called upwelling. During periods of gale force northwesterly winds, I’ve seen seawater temperatures along the immediate coastline drop nearly seven degrees in just one day.

Since 1976, temperature recorders housed in steel canisters and placed at fixed locations in the intertidal and subtidal zones near Diablo Canyon have recorded millions of seawater temperatures. Intertidal canisters are exposed to the air at minus low tide and underwater at high tide; the subtidal locations are always underwater. Depending on the weather, waves and tides, the temperature recorders are swapped out every few months.

During swap-out, new recorders are installed in the canisters and the old recorders taken back to the Diablo Canyon Ocean Lab to be downloaded to a computer database, serviced and calibrated.

At the Patton Cove monitoring station, which is just south of the power plant in approximately 10 feet of water, the average yearly seawater temperature is a cool 55 degrees Fahrenheit. The average minimum temperature usually occurs at this time of the year, and reaches a bone-chilling 49 degrees.

During the fall, the average maximum temperature can rise to the low 60s. The cold nutrient-rich upwelling also creates an amazingly productive ecological system along our coastline.

On days with plenty of sunshine and lots of upwelling, California giant kelp can grow up to 24 inches in just one day, ultimately reaching well over 150 feet in length. At that growth rate, you could almost see this type of algae grow in front of your eyes.

If you ever have a chance to dive on these kelp beds on a day with good seawater visibility, please do it. Rays of sunlight often beam through this underwater forest illuminating fish, invertebrates and the occasional marine mammal. It has been rightfully compared to flying near the ground through a redwood forest in Big Sur.

Because of upwelling, the waters along with the kelp beds and tide pools along San Luis Obispo County are some of the most biologically productive anywhere in the world.

To see some of the most beautiful coastal views found anywhere in California, “Lighthouse Jubilee!” is next Sunday, May 18th at the Point San Luis Lighthouse – with live music, local wine tasting, gourmet boxed lunch and an ice cream social-visit for details.

John Lindsey’s column is special to The Tribune. He is a media relations representative for PG&E and a longtime local meteorologist. He is president of the Point San Luis Lighthouse Keepers. If you have a question, send him an email at You can also followed him on