Federal forecasters have declared that the climate pattern known as El Niño, which caused warmer-than-normal ocean temperatures in the Eastern Pacific since June 2023, is officially over. The National Weather Service's Climate Prediction Center announced on Thursday that neutral conditions have returned, as expected. However, this respite is expected to be short-lived as the cooler counterpart, La Niña, is forecasted to develop this summer and persist throughout the winter in the Northern Hemisphere.

According to the National Oceanic and Atmospheric Administration (NOAA) ENSO blog, La Niña brings unusually cool ocean temperatures to the Pacific, with implications for weather patterns around the world. The NWS predicts a 65% chance of La Niña arriving between July and September, and an 85% chance of it persisting until January 2025. Although originally forecasted to begin in June, the rate of cooling has slowed in recent weeks, potentially aligning La Niña's arrival with the peak of Atlantic hurricane season, which may exacerbate the already predicted above-normal hurricane season.

NOAA has already forecasted an 85% chance of an above-normal hurricane season, with the largest number of storms ever predicted at this point in the season. Factors contributing to this forecast include near-record warm ocean temperatures in the Atlantic and the development of La Niña conditions in the Pacific. La Niña typically enhances Atlantic hurricane activity by reducing vertical wind shear, which can break apart developing storms. In contrast, El Niño achieves the opposite effect.

Notably, destructive hurricanes such as Katrina in 2005 and Andrew in 1992 occurred not during La Niña but in the neutral phase of the climate cycle. However, after hurricane season concludes, La Niña is expected to influence winter weather across the U.S., bringing warmer-than-average temperatures to the south and cooler-than-average temperatures to the north. This occurs due to changes in tropical rainfall and wind patterns triggered by La Niña's presence in the Pacific Ocean.

The implications of La Niña extend beyond the U.S., as its influence on global atmospheric circulation impacts weather patterns worldwide. In the U.S., La Niña usually results in cooler and wetter conditions in southern and interior Alaska and the Pacific Northwest, while the southern part of the country, from California to the Carolinas, tends to experience warmer and drier weather. The Ohio and Upper Mississippi River valleys may also receive above-average precipitation.

Additionally, La Niña affects marine ecosystems, making the waters off the Pacific colder and more nutrient-dense. This attracts cold-water species, such as squid and salmon, to the California coast and other regions, according to the National Ocean Service.

La Niña conditions have also been associated with a higher frequency of spring tornadoes in the central U.S., further emphasizing the broad-ranging impacts of this climate phenomenon.

While La Niña is not a storm that directly hits a specific area at a given time, its global influence on weather patterns can lead to significant disruptions. Scientists refer to La Niña as one part of the El Niño-Southern Oscillation (ENSO) cycle, a natural climate pattern characterized by alternating warm and cool phases of oceanic and atmospheric conditions in the Pacific.

As the world continues to experience extreme weather events, it is important to consider these climatic patterns within the context of human-induced climate change. The World Meteorological Organization notes that the past nine years have been the warmest on record, even with the cooling influence of the recent La Niña phase. Climate experts predict that 2024 will be one of the five hottest years ever recorded, potentially leading to more climate-driven disasters.

As the situation develops, NOAA plans to release its next forecast on La Niña in mid-July. It is crucial to remain vigilant about the potential impacts of La Niña on global weather patterns and to continue addressing the broader challenge of climate change.