Weather Watch

Goodbye, El Niño; hello, La Niña

With summer under way, a new rain season beginning Thursday and the Mid-State Fair just around the corner, I thought it would be interesting to look at the long-range forecast.

The moderate El Niño condition (warmer than normal ocean water in the equatorial and eastern Pacific), which shifted the position of the jet stream further south, thereby directing more Pacific storms toward the Central Coast last winter, has ended.

Over the last few months, ocean water temperatures have decreased. In fact, the National Oceanic and Atmospheric Administration’s Climate Prediction Center in Camp Springs, Md., has issued a La Niña watch (colder than normal ocean water in the equatorial and eastern Pacific) for late summer into the fall and winter as ocean water temperatures are expected to continue to diminish.

Normally the seawater temperature at the Diablo Canyon nuclear power plant averages 52.1 degrees during the month of May. This May the average was 51 degrees.

This shift can have profound ramifications all around the world.

There is a good chance that the Central Coast will experience normal temperatures this summer. The average maximum temperature at the Paso Robles airport during July is 94 degrees, while the average maximum temperature in Atascadero in July is 86 degrees, according to the Air Pollution Control District’s monitoring station there. San Luis Obispo is cooler, with an average July maximum temperature of 78 degrees at Cal Poly.

Unfortunately, this condition, combined with another large-scale ocean water temperature cycle, can also produce lower-than-average winter rainfall.

The other large-scale ocean water temperature cycle is the Pacific Decadal Oscillation (PDO), which can increase or decrease the La Niña effect. The PDO is found primarily in the North Pacific. The phases of the PDO are called warm phases or cool phases.

Unlike El Niño and La Niña, the PDO stays in one phase for a lot longer — between 10 and 40 years. The El Niño and La Niña phase usually last for about a year or so. It appears that we are still in the cool phase of the PDO, which means it should increase the La Niña effect and produce a greater chance of below-normal rainfall. These are long-range forecasts and should be taken with a grain of salt. Only time will tell the story.

A La Niña condition can also help produce an active hurricane season as it diminishes the hurricane-killing wind shear in the upper atmosphere that often shuts down any tropical cyclones that try to form in the Western Atlantic and Eastern Pacific oceans.

This condition, combined with a region of unusually warm water in the eastern Atlantic Ocean that is currently reported, could produce a vigorous hurricane season. This is not good news for those desperately trying to contain the largest oil spill in United States history in the Gulf of Mexico.

Today’s weather

A weak 1,009-millibar thermal low-pressure system will remain nearly stationary over the Central Coast through Monday.

This low-pressure system will diminish the northwesterly (onshore) winds along our coastline. This condition will allow the interior to warm up to the mid-90s but will also produce a stubbornly persistent marine layer along the beaches.

Today’s and Monday’s temperatures will range from the mid-90s in the interior to the high 70s and the low 80s in the coastal valleys under mostly sunny skies this afternoon. Temperatures along the beaches will range from the high 50s to the mid-60s.

A 1,034-millibar Eastern Pacific high will move eastward toward California and set up a steep pressure gradient along our coastline later Tuesday. This pressure gradient will produce strong to gale- force (25 and 38 mph) northwesterly (onshore) winds late Tuesday into Friday.

This vigorous onshore flow will produce a cooling trend in the interior as cooler marine air flows through the Salinas Valley and the Templeton Gap into the North County. These gusty winds will also produce a greater amount of clearing and warmer temperatures along the southwesterly (Avila Beach and Cayucos) facing beaches.

Temperatures will climb back to about average for the July Fourth holiday weekend. It’s still too early to forecast the situation along our beaches for fireworks displays.

Today’s surf report

The wind fields have shifted northward, leaving behind a 4- to 5-foot northwesterly (295-degree deep-water) swell (with an 8- to 10-second period) today. This northwesterly swell will increase to 5 to 7 feet (with an 8- to 11-second period) Monday through Tuesday morning.

Increasing northwesterly winds will generate a 6- to 8-foot northwesterly (310-degree deepwater) sea and swell (with a 5- to 9-second period) along our coastline later Tuesday, increasing to 7 to 9 feet Wednesday through Friday.

Hurricane Celia produced maximum sustained winds of almost 160 mph about 700 miles southwest off the southern tip of the Baja California peninsula Friday. This tropical cyclone will produce a 4- to 5-foot southerly (180-degree deep-water) swell (with a 12- to 15-second period) along our coastline tonight into Tuesday morning.

Arriving from the Southern Hemisphere:

Today’s 1- to 3-foot southern hemisphere (200-degree deepwater) swell (with a 14- to 16-second period) will overlap Monday’s hurricane swell from due south.

Seawater temperatures will range between 52 and 54 degrees through today, increasing to 53 to 55 degrees Monday through Tuesday. Seawater temperatures will decrease Wednesday through Friday.

Conservation tip

Summer means higher temperatures and more use of air conditioning. Learn easy ways to save money during this high-demand time. Find all the ways Pacific Gas and Electric Company helps you save at www.pge.com/seasontosave.

John Lindsey is a media relations representative for PG&E. He is also a local weather expert and has lived along the Central Coast for more than 23 years. If you have a question, send him an e-mail at pgeweather@pge.com.

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