It’s official: the notorious El Niño is here.

The ocean phenomenon is once again warming the tropical Pacific, scientists at the National Oceanic and Atmospheric Administration announced Thursday, bringing with it the possibility of more rain for Orange County.

“It’s back,” said Michelle L’Heureux, head of NOAA’s “Enso” — El Niño Southern Oscillation — team in Maryland. “An El Niño advisory means that El Niño conditions are observed and expected to continue. We issued, for the first time today, an El Niño advisory.”

But don’t bring out the rain slicker just yet. While El Niño has helped push rainstorms our way during winter in past years, everything depends on just how strong this year’s El Niño will become.

So far, L’Heureux said, scientists are predicting a weak to moderate El Niño influence lasting through the coming fall, possibly strengthening into winter. “We don’t know yet,” she said.

“California is kind of interesting, because you guys are fairly sensitive to how strong El Niño will be,” she said. “If it’s a weak or even normal El Niño, it’s kind of hit and miss.”

Odds are Southern California will receive at least normal rainfall if El Niño remains weak to moderate, but it could also mean more or, in some cases, perhaps even less rain.

“If we get a strong El Niño, you will get above-average precipitation,” she said.

El Niño has its dark side. A strong one could cause intense storms and flooding, as it did in 1997-98.

But so far, that doesn’t appear to be the case this year. And with county rainfall running three to six inches below average, some El Niño-influenced rain would be welcome.

The warm-water influence also could have affect Southern California fisheries, said Sam McClatchie, a NOAA fisheries oceanographer in Southern California. It could, for example, reduce the catch in California’s important squid fishery, valued at $22.4 million last year — although McClatchie said he could not predict how much.

And species not often seen this far north, such as marlin, could be enticed into California waters.

The scientists have been watching El Niño form for months. Ocean temperatures in the tropical Pacific have been warming since the start of the year, the beginning of a transition out of La Niña conditions — the opposite of El Niño, when the tropical waters grow colder.

March, April and May were considered “Enso neutral.” June temperatures began to qualify as El Niño.

While complex weather and climate factors influence rainfall in Southern California, La Niña likely helped worsen dry weather here.

“I would finger that as a suspect,” L’Heureux said. “La Niña can lead to a decrease in rainfall, especially over Southern California.”

(Register photo of kayaker paddling along Pomona Avenue in Costa Mesa in 1997 by Steve Zylius.)

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