This year’s unusual El Niño just got even stronger

Temperatures in the Pacific Ocean are still rising as this year’s El Niño strengthens.

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A monthly outlook published Thursday by the National Oceanic and Atmospheric Administration’s Climate Prediction Center gives a 75% chance that El Niño will become “historic” from October to December.

Even since August, forecasters have lifted the odds of El Niño exceeding the strength of all previous events on record since 1950.

“It’s not the hottest yet, but it could become the hottest,” Alexander Gershunov, a research meteorologist at the Scripps Institution of Oceanography at UC San Diego, told SFGATE. “It hasn’t matured yet completely. It’s going to mature over the next few months as far as sea surface temperatures go.”

The spike in the Pacific’s heat during El Niño years can drive winter weather in California and across the globe. Technically, El Niño is the warm phase of a natural pattern that emerges in the central and eastern tropical Pacific. During El Niño conditions, weak winds are associated with above-average ocean surface temperatures. Year to year, this seasonal phenomenon alternates with an opposite phase, La Niña, and with neutral conditions. 

This El Niño emerged in June. By August, the Climate Prediction Center reported a greater than 90% chance that El Niño would rank as “very strong” during the upcoming fall and winter. Thursday’s report was largely the same, but it raised the previous 69% chance that this El Niño will break strength records up to a 75% chance of that outcome. 

Michelle L’Heureux, a physical scientist for the Climate Prediction Center, explained the relationship between the strength of the event and its impacts on the climate. 

“Stronger El Niño events can only make certain outcomes more likely; they do not guarantee them,” L’Heureux wrote to SFGATE. “Also stronger El Niño events do not necessarily make the impact more intense — for example, we cannot say that El Niño will lead to more intense rainfall over someone’s house. But we can say that more rainfall, particularly weather events that repeat or recur over the course of a season, can be made more likely by El Niño.”

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El Niño’s global effects vary widely depending on the region. In California, residents pay the most attention to the event’s influence on winter rain and snow. Generally, El Niño causes the jet stream over the Pacific to shift southward, raising the odds of a wetter season in Southern California. The Climate Prediction Center’s seasonal outlook does indeed show a lean toward above-average precipitation for Southern California from October to December. Those odds of rain and snow not only rise but also spread across all of California this winter.  

L’Heureux explained that the timing of this precipitation will likely trail behind El Niño’s peak strength in the ocean. “The outlooks show that the strongest probabilities for increased precipitation in California are during December-March,” L’Heureux wrote. “There is generally a slight lag between the Pacific [sea surface temperatures] and the impacts over the United States.”

There are many other impacts on California that scientists expect to emerge in the coming months. El Niño has also already intensified the eastern Pacific hurricane season, devastating the Hawaiian Islands and pushing massive waves into Southern California. Biologists are bracing against the severe consequences anticipated for marine ecosystems, which have already been under strain from a persistent marine heat wave in California waters. 

And oceanographers are also expecting El Niño to temporarily raise sea levels and bump up winter wave energy, threatening the coastline with erosion and flooding, especially during storms. 

After El Niño first emerged earlier this year in the waters along the equator in the Pacific, experts now say they’ve likely found the first evidence that the event has started to affect the waters off California’s coast, too. Daniel Rudnick, a physical oceanographer for Scripps, told SFGATE that unusual heat in deep water off the Southern California coast has appeared in recent weeks; it likely doesn’t belong to the existing marine heat wave. He’s tracking the trends closely with robotic underwater gliders. 

“I’m actually starting to see one of the signs of El Niño arriving,” Rudnick told SFGATE. “Up until recently, the heat anomaly has mainly been in the upper 100 meters. I’m starting to see it go deeper, and that is a sign of El Niño.”