La Niña Has Ended, and El Niño May Be on the Way

La Niña, the climate pattern that helped fuel the extremely active hurricane seasons and drought in the southwest over the past two and a half years, has ended, the National Oceanic and Atmospheric Administration said Thursday.

The intermittent phenomenon — which occurs when sea-surface temperatures in the equatorial Pacific Ocean are below average — typically brings drier, warmer conditions to the southern half of the United States and wetter weather to the northern half. The last La Niña began in September 2020.

But last month, sea-surface temperatures in that part of the ocean rose, scientists say, signaling the end of La Niña and the start of a new neutral climate pattern (this occurs when the sea-surface temperatures are at or near average). But this neutral period may be short-lived: By summer, rising sea-surface temperatures could lead the opposing El Niño pattern to develop, according to NOAA’s Climate Prediction Center. By the fall, forecasters believe, there is a 62 percent chance El Niño will form.

The World Meteorological Organization has also said that a warming El Niño event may develop in the coming months, bringing with it another spike in global temperatures that had been kept partly at bay by La Niña’s cooling effect.

La Niña and El Niño are the opposite phases of what is called the El Niño-Southern Oscillation, or ENSO. During an El Niño period, it can be dryer and warmer than usual in the northern United States, and wetter and more likely to flood along the U.S. Gulf Coast and in the Southeast. Previous El Niños have helped unleash rain in California, fires in the tropics and floods in the southern United States.

So what does all of this mean for what is in store across the United States for the rest of the year? Scientists say that it can be hard to predict, and that it is unclear what impact climate change might be having on weather patterns.

“The old La Niña playbook and the old El Niño playbook don’t seem to be as reliable as they used to be,” said Jan Null, an adjunct professor of meteorology at San Jose State University. But, he added, you would typically expect the southern tier of the United States to be wetter than normal, and the Pacific Northwest to be drier than normal.

Philip Klotzbach, a meteorologist with Colorado State University, has anticipated that El Niño could help to reduce the severity of this year’s Atlantic hurricane season by increasing rapid changes in wind velocity and direction, which, he said on Twitter, “tears apart hurricanes.”

An El Niño pattern, which sends warm water surging from the west to the east side of the Pacific Ocean, can also increase the risk of flooding and coastal erosion in Southern California, as well as beach hazards like debris washing ashore and rip currents, scientists say.

The weather pattern can also affect marine life off the Pacific Coast, halting or weakening a process known as upwelling, which brings water and nutrients to the surface of the ocean, according to NOAA. This can have a knock-on effect on phytoplankton, fish and other marine life. The warmer waters may also draw tropical species into areas that are normally too cold.