NOAA's Climate Prediction Center on Thursday declared an end to the long-lasting La Niña that began nearly three years ago, signaling that ocean temperatures in the equatorial Pacific were warming up.
The La Niña pattern, the colder counterpart of El Niño in the El Niño-Southern Oscillation climate phenomenon, has influenced the weather across the Northern Hemisphere in a number of ways in recent years.
The unusually long-lasting nature of the phenomenon led to the unofficial nickname of a "triple-dip La Niña" as it persisted through three winter seasons. Conditions were first observed in the central Pacific in the three-month stretch from July through September 2020, and they continued nearly uninterrupted for 30 months. This is just shy of the La Niña from 1998 to 2001, which lasted 32 months, according to AccuWeather senior meteorologist Dan Pydynowski.
La Niña occurs when the water temperatures in the eastern equatorial Pacific Ocean are at least 0.9 of a degree Fahrenheit (0.5 of a degree Celsius) below average over three months. Conversely, El Niño happens when the running average is 0.9 of a degree Fahrenheit (0.5 of a degree Celsius) or higher. Neutral conditions exist for any departure between those two temperature ranges.
While it may seem like such a small change in water temperature in one part of the world would have only a minimal impact elsewhere, it can significantly alter global wind patterns, which drive the development and movement of storm systems and moisture across the globe.
During La Niña, the southern United States tends to experience warmer and drier conditions than usual, while the northern U.S. can be wetter and colder. It can also lead to an above-average number of tropical storms and hurricanes in the Atlantic basin as it makes conditions more favorable for storm development.
In 2020, a record-setting hurricane season unfolded in the Atlantic, with forecasters using more names to identify storms than ever before. Another above-normal season followed in 2021. However, the 2022 season produced 14 storms, which is around average.
The CPC is forecasting neutral conditions, neither La Niña nor El Niño, to continue through the spring months and into the early summer.
Since neutral conditions are expected for a few months, the effects that the ocean temperatures in the central Pacific have on the weather patterns globally will be diminished.
Later this summer or in the fall, El Niño conditions are forecast to emerge, according to AccuWeather's team of long-range forecasters. This, too, will have vast implications for weather patterns across the Northern Hemisphere for the second half of 2023 and beyond.
An El Niño tends to lead to wetter conditions than usual across the southern United States and warmer, drier conditions in the northern United States. Stronger El Niños can amplify those effects, leading to destructive flooding in some areas and severe drought in others. Strong El Niños have recently been observed from 1997 into early 1998 and from 2015 into early 2016.
"Other ocean and weather patterns that extend over many years across parts of the Pacific can determine how strong an El Niño becomes," said AccuWeather lead long-range forecaster Paul Pastelok. "As of now, it appears the developing El Niño may not be a strong or even moderately strong one for the rest of the year."
One limiting factor as to why AccuWeather forecasters do not expect a rapid turn toward El Niño conditions in the equatorial Pacific is the lingering chilly waters across much of the eastern Pacific.
"The predominant flow along the West Coast can shove these cooler waters southward, limiting the warming potential in the equatorial Pacific," AccuWeather meteorologist Brandon Buckingham said. "We do expect a neutral to gradual turn toward El Niño conditions through the spring and summer months, but again, this can be a gradual warmup rather than a sudden" increase.