As La Niña continues to strengthen in the tropical Pacific, meteorologists warn the climate pattern could leave California facing another drought in the coming months.
La Niña is the drier component of the El Niño Southern Oscillation, or ENSO, system that drives climate and weather patterns around the world. Its warm, humid counterpart, El Niño, last occurred from July 2023 through this spring and was linked to record-warm global temperatures and an unusually wet winter in California.
Although ENSO conditions are currently neutral, La Niña appears to be getting closer. According to the National Oceanic and Atmospheric Administration, there is a 66% chance it will develop between September and November, and a 74% chance it will survive the winter.
On the east coast that could mean that ongoing active hurricane seasonBut in the West, and particularly Southern California, it could be a sign of drought returning.
“Droughts are waning and developing again, and a lot of that is related to La Niña,” said Brad Pugh, a meteorologist with NOAA’s Climate Prediction Center. “The good news is [California’s] Currently, drought conditions are no longer present, but with La Niña expected this winter, Southern California and the Southwest are vulnerable to a resurgence of drought.”
La Niña last occurred from 2020 to 2023 — a period that saw California experience its driest in three years. The dry spell caused reservoirs to shrink to record lows, led to the strictest water restrictions ever in Southern California and contributed to the state’s worst wildfire seasons on record.
There has already been some decline in drought in recent months, partly because record breaking heat removes moisture from the air and landscape.
Over the past eight weeks, “the demand for moisture from the atmosphere has been exceptional due to the high temperatures,” Pugh said.
The latest update from the US Drought Monitor shows that about 17% of California is now considered abnormally dry, compared to just over 1% three months ago.
Read more: July was the hottest month on record in California as the climate warms to dangerous new extremes
However, there are no guarantees.
La Niña only increases the chance of drought, but it is no guarantee that it will actually happen. Moreover, its arrival has already been delayed compared to earlier predictions.
In fact, a few months ago, there was a good chance that El Niño would quickly transition into La Niña this summer.
“The thinking was that by this point in the summer we would probably be in — or close to — a La Niña,” said Tom DiLiberto, an ENSO weatherman with NOAA. “That’s clearly not the case yet. We’re still expecting it to happen, now into the fall.”
The slow start could be because the planet’s oceans are taking longer to cool after reaching record high temperatures over the past year. La Niña is defined in part by periods of below-average surface temperatures in the Pacific Ocean, as well as a northward shift of the jet stream — the atmosphere’s racetrack for Pacific storms.
“We haven’t seen ocean temperatures adequately reflect that cooling … and we haven’t seen the atmosphere match it either,” DiLiberto said.
Still, he is confident that La Niña will occur because there is a large area of cooler-than-average water just beneath the surface of the Pacific Ocean that is “slowly but surely approaching the surface,” DiLiberto said.
“So the signs are still there,” he said. “It’s just, as opposed to jogging toward La Niña, we’re walking.”
Read more: LA’s water supply is in good shape. But is the city ready for the next drought?
The effects of La Niña are also not the same everywhere.
While the pattern is associated with drought in Southern California, the signal is more ambiguous in the Bay Area and the northern part of the state. In the Pacific Northwest, it often leads to wetter-than-average conditions.
Nathan Lenssen, a climate scientist at the National Center for Atmospheric Research and the Colorado School of Mines, said he hopes La Niña won’t lead to another year of drought for California, especially given the explosive forest fires already seen all over the state this year.
But he said people need to be prepared, both for droughts and other extreme weather events that are becoming more common due to human-caused climate change.
“What we also know is that major storms are getting more intense,” Lenssen said. “So for things like flooding, we’re not out of the woods yet, even with La Niña.”
He noted that La Niña also occurred during the state’s record-wet winter of 2022-23.
Read more: Ocean temperatures are out of control, and El Niño is only partly to blame
Those hoping for relief from the Earth’s smoldering heat will have to wait a little longer.
The latest seasonal forecasts released by NOAA predict above-normal temperatures for most of the continental United States through at least November. The greatest chance for above-normal temperatures is in New England and parts of the Southwest.
According to the weather forecast, the chances of temperatures above or below normal are equal on the West Coast and in the Pacific Northwest.
The lack of cooling and later onset of La Niña may also affect the overall temperature of the year.
According to Karin Gleason, chief monitoring officer at NOAA’s National Centers for Environmental Information, there is currently a 77 percent chance that 2024 will surpass 2023 as the warmest year on record on Earth. In addition, there is a nearly 100 percent chance that it will be among the five warmest years on record.
The forecast also points to continued drought, regardless of the timing of La Niña. The outlook shows that below-normal precipitation is likely through November in the Southwest and Southern California, as well as parts of the Great Plains.
Pugh of the Climate Prediction Center still expects La Niña to have an impact this fall.
However, its strength has yet to be determined. The models currently show a wide range of probabilities, ranging from weak to moderate.
“If La Niña continues through the winter, we would expect drier than normal conditions in Southern California and the Southwest,” Pugh said. “So I would say as we get through the winter, we could see drought conditions develop again in those areas.”
This story originally appeared in the Los Angeles Times.