May 26, 2018
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El Nino is increasingly likely, but its strength is in doubt

By Paul Rogers, San Jose Mercury News

SAN JOSE, Calif. — California, suffering through the third year of an oppressive drought, received good and bad news Thursday from scientists closely tracking the Pacific Ocean for El Nino, the phenomenon when ocean waters warm, often bringing wet winters to the state.

The chances of El Nino conditions developing by this fall are now 82 percent, up from 78 percent last month — and 36 percent since November — the National Oceanic and Atmospheric Administration announced.

But for the first time, NOAA scientists said, it looks like a moderate, not a strong, El Nino is developing. And historically, while strong El Ninos have nearly always brought soaking rains to California, moderate and weak ones only about half the time have delivered wetter-than-normal winters.

“The question now is what flavor of El Nino we’re going to get,” said Bill Patzert, a research scientist and oceanographer at NASA’s Jet Propulsion Laboratory in Pasadena. “I’ve got my money on this being El Wimpo.”

Generally speaking, the warmer the Pacific Ocean water along the equator, the higher likelihood there is of heavy rainfall during El Nino years. During mild El Nino years, when the ocean water is only slightly warmer than historic averages, there are just as many drier-than-average winters in California as soaking ones.

California desperately needs rain. Locked in the worst drought since the one that began in 1987 and ended in 1992, Gov. Jerry Brown declared a drought emergency in January. Reservoirs are low, and major cities received only about half their historic average rainfall this past winter.

San Francisco, for example, has received 12.53 inches, or 53 percent of average, since July 1. San Jose has had 6.34 inches, or 43 percent. Oakland is at 10.05 inches, or 49 percent. Fresno is at 4.81 inches, or 42 percent. And Los Angeles has received 6.08 inches, or 41 percent.

A long, hot summer looms.

Extreme wildfire risk, fallowed farmland and water restrictions in most cities are expected until November or later.

National Weather Service officials have forecast that this summer will be hotter than normal in California, where 100 percent of its land area is already listed by the federal government as in “severe drought.”.

Earlier this spring, scientists were tracking a huge pulse of warm water moving from Indonesia toward South America along the equator. The temperature and size of the mass, known as a Kelvin wave, brought comparisons to the last strong El Nino event in the winter of 1997-98, when California had soaking storms and rainfall totals that were double the historic average.

Now, the ocean near the equator is between 1.1 and 2.9 degrees Fahrenheit warmer than historic average levels. Those temperatures are above the 0.9 degrees Fahrenheit trigger point for El Nino. But scientists say they aren’t yet seeing the kinds of changes in the atmosphere that normally accompany an El Nino, such as winds consistently blowing from Asia toward the United States, and rainstorms moving from Indonesia toward the international date line.

“The ocean temperatures are warmer, but we are still waiting for the atmospheric conditions to kick in,” said Michelle L’Heureux, a meteorologist with the NOAA’s Climate Prediction Center in College Park, Md.

The waters could warm more, she said, and El Nino conditions could still strengthen. But if not, the track record for moderate El Ninos isn’t great.

Since 1950, there have been 16 moderate to weak El Ninos. They brought wetter-than-normal rainfall years seven times in San Francisco and Los Angeles. Over the same time, there have been six strong El Nino events. They brought wetter-than-normal winters five times to Los Angeles and four times to San Francisco.

“Historically, there is a better chance of having above-normal rainfall than if there were no El Nino,” said Jan Null, with Golden Gate Weather Services in Saratoga, which compiled the data. “But there are no guarantees.”

The next El Nino update from NOAA is due out July 10.

Distributed by MCT Information Services


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