As La Niña gathers strength in the tropical Pacific, forecasters are warning that the climate pattern could plunge California back into drought conditions in the months ahead. La Niña is the drier component of the El Niño Southern Oscillation system, or ENSO, which is a main driver of climate and weather patterns across the globe. Its warm, moist counterpart, El Niño, was last in place from July 2023 until this spring, and was linked to record-warm global temperatures and California’s extraordinarily wet winter. Though ENSO conditions are neutral at the moment, La Niña’s arrival appears increasingly imminent. There is a 66% chance it will develop between September and November and a 74% chance that it will persist through the winter, according to the National Oceanic and Atmospheric Administration.
On the East Coast, that could mean a continued active hurricane season. But in the West — and particularly in Southern California — it could signal a return to dryness ahead. “Drought episodes do wane and redevelop, and a lot of that is associated with La Niña,” said Brad Pugh, a meteorologist with NOAA’s Climate Prediction Center. “The good news is [California’s] out of drought currently, but with La Niña forecast through the winter, Southern California and the Southwest will be vulnerable for a redevelopment of drought.”
La Niña only tilts the odds toward dryness — it doesn’t ensure it — and its arrival has already been delayed from earlier projections. In fact, just a few months ago, there was a high likelihood that El Niño would quickly transition into La Niña this summer. “The thought was we would be probably in — or close to in — a La Niña by this point of summertime,” said Tom DiLiberto, an ENSO forecaster with NOAA. “We’re clearly not yet. We’re still expecting it to emerge, now in the fall.” The sluggish start could be because the planet’s oceans are taking longer to cool after soaring to record-high temperatures over the last year.
La Niña is partly defined by periods of below-average surface temperatures in the Pacific, as well as a northward shift of the jet stream — the atmosphere’s racetrack for storms from the Pacific. “We haven’t seen both the ocean temperatures reflect that cooling enough ... and we also haven’t seen the atmosphere hook on,” DiLiberto said. Still, he is relatively confident La Niña will emerge because there is a large area of below-average-temperature water just beneath the surface of the Pacific Ocean, which is “slowly but surely approaching the surface,” DiLiberto said.
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