Jun 13 2016

Why the ocean water along the Central Coast turned cold

As most beachgoers will tell you, the seawater temperatures along the Central Coast have turned downright cold.

In fact, the harbor seals and sea lions seem to want to spend more time on the rocks and beaches. My children, Chloe and Sean, are using thicker wetsuits.

So why is the seawater so cold?

Strong to gale-force northwesterly winds have produced greater amounts of upwelling along the coastline.

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 this past “Godzilla” El Niño has died. Region 3.4 is the standard for classifying El Niño (warmer-than-normal SST) and La Niña (cooler-than-normal SST) events. The fortunetelling 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 2.0 degrees Celsius (or 3.6 degrees Fahrenheit), a very rare event indeed.

Last winter’s temperatures reached a little over 3 degrees Celsius, one of the strongest on record.

William Patzert, a respected climatologist with Caltech’s NASA Jet Propulsion Laboratory in Pasadena, said, “Unfortunately, its effects weren’t as great as the 1997-98 El Niño. That cycle produced huge amounts of rain and snow. This year’s El Niño was no Godzilla, more of a gecko as far as impacts were concerned along the Central Coast.”

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 latest model runs from NOAA’s Climate Prediction Service indicate that we will go into a La Niña cycle by July and remain in this cycle through early 2017.

The good news is that upwelling brings nutrients to the surface waters off the coast, allowing fish populations living in these waters to thrive. The bad news is this condition often shifts the storm track farther north into the Pacific Northwest, leaving the Central Coast high and dry with below-average rainfall.

However, there have been periods of heavy rain during neutral conditions (“El Nothing”) and La Niña cycles. An atmospheric river (Pineapple Express) could develop over the Central Coast during winter and produce copious amounts of rain along the Central Coast, regardless of ENSO.

Otherwise, chances are, we will probably see another year of below-average rainfall. Only time will tell the story.

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