El Niño conditions in the tropical Pacific Ocean are gaining strength. The latest forecast signals a moderate to strong event come fall or winter, raising hope for drought-parched San Diego County.
While similar indications were reported last year at this time, this year is shaping up to be different, said David Pierce, climate researcher with Scripps Institution of Oceanography. That said, it’s still too early to know for sure, he added.
“You have to have both the ocean and the atmosphere cooperating together,” Pierce said. “Last year the ocean surface temperatures and the subsurface temperatures below the surface looked like it was going to be an El Niño, but the atmosphere didn’t really start responding. But this year is a little bit different. The atmosphere does seem to be responding.”
Pierce said El Niño is set in motion when massive convective storms form over the warmer-than-usual tropical Pacific.
“It’s kind of like if you roll a ball down a hill and there’s a lot of people around, “ Pierce said. “Someone might run up and kick it and deflect it from its path. So we’re rolling down hill, we’re aiming towards an El Niño, but random weather events can still make a difference.”
He said large storms such as typhoons could knock El Niño off of its trajectory. They could also add to its strength.
“Like in 1997 to ’98, we had a very strong El Niño,” Pierce said. “And that was partly because there were these incredible winds out in the tropical Pacific that really increased the amplitude of that.”
Pierce said current tropical surface temperatures are approximately 3 degrees warmer than usual. During the large El Niño in the late 1990s, ocean temperatures reached 8 degrees above normal.
“We’re not at that point yet, but you don’t expect that because we’re really early in the season,” Pierce said.
He said one of the biggest indicators of a coming strong El Niño is the subsurface ocean temperatures.
“When you have all this warm water down to a couple hundred feet, it’s a really big signal,” Pierce said. “It can really affect the overlying atmosphere. So right now we’re in one. It’s got these pretty strong signals.”
El Niños occur about every four to 12 years. A moderate or strong event can cause above-average rainfall in San Diego as well as potentially damaging waves along the coast. The event can last from nine months to two years.
An El Niño doesn’t always guarantee a wet year in San Diego County. During the last El Niño in 2010, San Diego received 10 inches of rain, which is average, but it produced a significantly stronger than usual wave energy, causing 36 percent more erosion along California's shorelines than an average winter.
“When you have a strong El Niño, it tends to be wetter in Southern California by about 20 to 30 percent,” Pierce said.
During the strong 1997 and 1998 event, San Diego received 17 inches of rain. In 1993, a strong El Niño was credited with dumping 18 inches at Lindbergh Field.
