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La Niña is likely to arrive this summer. Here's what that means for hurricane season

A satellite image provided by the National Oceanic and Atmospheric Administration shows Hurricane Idalia, center, over Florida and crossing into Georgia, and Hurricane Franklin, right, as it moves along off the East coast of the U.S., on Aug. 30, 2023.
A satellite image provided by the National Oceanic and Atmospheric Administration shows Hurricane Idalia, center, over Florida and crossing into Georgia, and Hurricane Franklin, right, as it moves along off the East coast of the U.S., on Aug. 30, 2023.

El Niño is so last season.

Federal forecasters say the climate pattern, which brought warmer-than-normal ocean temperatures to the Eastern Pacific — and helped drive global temperatures to new heights — since June 2023, is officially over.

The National Weather Service’s Climate Prediction Center declared Thursday that neutral conditions returned during the past month, as expected.

But they’re not likely to last long: El Niño’s cooler counterpart, La Niña, is forecast to develop this summer and persist throughout winter in the Northern Hemisphere.

“The tropical Pacific’s climate pendulum appears to be swinging back toward its other extreme,” reads a Thursday post on the National Oceanic and Atmospheric Administration’s (NOAA) ENSO blog, which focuses on this specific phenomenon.

La Niña brings unusually cool ocean temperatures to the Pacific, with implications for weather all over the world. The NWS says there’s a 65% chance it will arrive between July and September and an 85% chance it lingers until January 2025.

Forecasters originally predicted that La Niña could begin as soon as June, but shifted their timeline as the rate of cooling has slowed in recent weeks.

That means she could reasonably make her grand entrance right as peak Atlantic hurricane season rages — and potentially exacerbate it.

La Niña conditions are especially conducive to Atlantic hurricanes

NOAA has already predicted an 85% chance of an above-normal hurricane season, which lasts from June through November. Last month, it forecast between 17 and 25 named storms — the largest number of storms ever predicted by the agency by this point in the season. (There were 20 such storms in 2023, the fourth-highest year since 1950.)

Forecasters pointed to a number of factors, including near-record warm ocean temperatures in the Atlantic and the development of La Niña conditions in the Pacific.

La Niña historically enhances Atlantic hurricane activity by tamping down the vertical wind shear in the tropics. Strong wind shear, which happens when the wind conditions change rapidly, breaks apart developing storms.

Think of it this way: La Niña usually means stronger hurricane activity in the Atlantic basin and suppressed hurricane activity in the central and eastern Pacific basins. El Niño achieves the opposite.

“The hurricane impacts of El Niño and its counterpart La Niña are like a see-saw between the Pacific and Atlantic oceans, strengthening hurricane activity in one region while weakening it in the other,” according to a 2014 ENSO blog post.

Interestingly, the NWS notes that some of the most destructive hurricanes to hit the U.S. in recent decades — like Katrina in 2005 and Andrew in 1992 — occurred not during La Niña, but in the neutral phase of the cycle.

What La Niña could mean for winter temps across the U.S.

During La Niña, the Pacific jet stream often meanders high into the North Pacific, as seen in this visual from NOAA.
/ National Oceanic and Atmospheric Administration
National Oceanic and Atmospheric Administration
During La Niña, the Pacific jet stream often meanders high into the North Pacific, as seen in this visual from NOAA.

After hurricane season wraps, La Niña is likely to play a role in winter weather across the U.S., bringing warmer-than-average temperatures to the south and cooler-than-average temperatures to the north.

As NOAA explains, its arrival in the Pacific Ocean triggers changes in tropical rainfall and wind patterns that have a ripple effect on the rest of the world. In the U.S., that usually involves a shift in the path of mid-latitude jet streams, which affects temperature and precipitation.

“During La Niña, the Pacific jet stream often meanders high into the North Pacific and is less reliable across the southern tier of the United States,” the agency says.

As a result, southern and interior Alaska and the Pacific Northwest can be cooler and wetter than normal, and the southern part of the country — from California to the Carolinas — tends to be extra warm and dry. The Ohio and Upper Mississippi River valleys may also be wetter than usual.

La Niña also makes the waters off the Pacific colder and more nutrient-dense than usual, which attracts more cold-water species — think squid and salmon — to the California coast and other locations, the National Ocean Service says.

La Niña conditions have also been linked to a higher frequency of spring tornadoes in the central U.S.

The NWS says both La Niña and El Niño tend to be strongest from December to April, “because the equatorial Pacific sea-surface temperatures are normally warmest at this time of the year.”

More detailed predictions about La Niña are likely on the horizon, as NOAA plans to release its next forecast in mid-July.

Global temperatures are still rising, even in a cooler climate pattern

It’s important to remember that climate patterns like La Niña and El Niño, which fluctuate naturally, are happening in the broader context of human-induced climate change — which makes weather more extreme all over the world.

The World Meteorological Organization pointed out earlier this month that the past nine years have been the warmest on record, even with the “cooling influence of a multi-year La Niña from 2020 to early 2023.” In fact, 2023 was the hottest year ever recorded.

WMO Deputy Secretary-General Ko Barrett said in a statement that weather will continue to be extreme because of the extra heat and moisture in the atmosphere.

“The end of El Niño does not mean a pause in long-term climate change as our planet will continue to warm due to heat-trapping greenhouse gases,” she said. “Exceptionally high sea surface temperatures will continue to play an important role during next months.”

Scientists predict that 2024 will be one of the five hottest years ever recorded, bringing another scorching summer and the potential for even more climate-driven disasters.

The name — and the phenomenon — explained

Scientists stress that La Niña is not a storm that hits a specific area at a given time. Instead, it's a change in global atmospheric circulation that affects weather around the world.

"Think of how a big construction project across town can change the flow of traffic near your house, with people being re-routed, side roads taking more traffic, and normal exits and on-ramps closed," states a NOAA webpage. "Different neighborhoods will be affected most at different times of the day. You would feel the effects of the construction project through its changes to normal patterns, but you wouldn't expect the construction project to 'hit' your house."

It's one part of the El Niño-Southern Oscillation (ENSO) cycle, a natural climate pattern defined by opposing warm and cool phases of oceanic and atmospheric conditions in the Pacific. In the ENSO cycle, La Niña and El Niño alternately cool and warm large areas of the tropical ocean about every two to seven years on average.

Forecasters can officially declare a La Niña event when sea surface temperatures clock in below a certain level, are modeled to remain under that threshold and prompt a noticeable atmospheric response, like changes in winds.

As for the names: South American fishermen had long observed warmer-than-normal coastal Pacific Ocean waters and dramatic decreases in fish catch around Christmastime.

They nicknamed that phenomenon El Niño — Spanish for "little boy" — after baby Jesus. So when scientists discovered the opposite phase of El Niño in the 1980s, they called it “little girl,” or La Niña.

Copyright 2024 NPR

Rachel Treisman (she/her) is a writer and editor for the Morning Edition live blog, which she helped launch in early 2021.