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Rock fish

A rock fish near Diablo Canyon Power Plant.

If you’re planning to head to the Central Coast to enjoy the ocean, you may want to bring a thicker wetsuits and here’s why.

As most beachgoers will tell you, the seawater temperatures along the Central Coast have turned downright cold this spring as moderate gale-force to fresh-gale force (32 to 46 mph) northwesterly winds blow along the California shoreline and produced great amounts of upwelling.

In fact, the harbor seals and sea lions seem to want to spend more time on the rocks and beaches.

At the Patton Cove seawater monitoring station, which is just south of the Diablo Canyon Power Plant in approximately 10 feet of water, the average seawater temperature this April has averaged a cool 52 degrees Fahrenheit. The minimum temperatures usually occur at this time of the year with the spring winds, and can reach a bone-chilling 47 degrees. The warmest seawater temperatures of the year happened in fall, when seawater temperatures can reach the mid-60s.

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 to the surface along the immediate shoreline.

Farther away, another factor may help to keep seawater temperatures at normal or below normal: It’s called El Niño-Southern Oscillation (ENSO). The latest surface seawater temperature (SST) data from the central equatorial region of the Pacific Ocean called Niño 3.4 indicates that a La Niña condition is still present.

Region 3.4 is the standard for classifying El Niño (warmer-than-normal SST) and La Niña (cooler-than-normal SST) events. The fortune-telling SST cycles in Niño 3.4 are categorized by the amount they deviate from the average SST. In other words, an anomaly.

A weak El Niño is classified as an SST anomaly between 0.5 and 0.9 degrees Celsius, a moderate El Niño is an anomaly of 1.0 to 1.4 degrees Celsius and a strong El Niño ranges from 1.5 to 1.9 degrees Celsius. A very strong El Niño anomaly is anything above or 3.6 degrees Fahrenheit, a very rare event indeed.

John Lindsey

John Lindsey

For reasons we really don’t understand, pressure areas change places at irregular intervals over the equatorial Pacific. This is part of the broader El Niño-Southern Oscillation climate pattern.

During a La Niña phase, high pressure builds in the eastern equatorial Pacific, while low pressure develops to the west, producing a stronger equatorial pressure gradient. Almost like a car rolling downhill, the easterly trade winds strengthen, causing upwelling off the coastlines of Peru and Ecuador and lowering sea surface temperatures throughout the eastern Pacific Ocean.

The good news is that upwelling brings nutrients to the surface waters off the coast, allowing fish populations living in these waters to thrive.

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John Lindsey is Pacific Gas and Electric Co.’s Diablo Canyon Power Plant marine meteorologist and a media relations representative.

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