Whether that’s a relief or not depends in part on where you live. Above-normal temperatures are still forecast across the U.S. in summer 2024. And if you live along the U.S. Atlantic or Gulf coasts, La Nina can contribute to the worst possible combination of climate conditions for fueling hurricanes.

Pedro DiNezio, an atmosphere and ocean scientist at the University of Colorado who studies El Nino and La Nina, explains why and what’s ahead.

What is La Nina?

La Nina and El Nino are the two extremes of a recurring climate pattern that can affect weather around the world.

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Forecasters know La Nina has arrived when temperatures in the eastern Pacific Ocean along the equator west of South America cool by at least half a degree Celsius (0.9 Fahrenheit) below normal. During El Nino, the same region warms instead.

Those temperature fluctuations might seem small, but they can affect the atmosphere in ways that ripple across the planet.

The tropics have an atmospheric circulation pattern called the Walker Circulation, named after Sir Gilbert Walker, an English physicist in the early 20th century. The Walker Circulation is basically giant loops of air rising and descending in different parts of the tropics.

Normally, air rises over the Amazon and Indonesia because moisture from the tropical forests makes the air more buoyant there, and it comes down in East Africa and the eastern Pacific. During La Nina, those loops intensify, generating stormier conditions where they rise and drier conditions where they descend. During El Nino, ocean heat in the eastern Pacific instead shifts those loops, so the eastern Pacific gets stormier.

El Nino and La Nina also affect the jet stream, a strong current of air that blows from west to east across the U.S. and other mid-latitude regions.

During El Nino, the jet stream tends to push storms toward the subtropics, making these typically dry areas wetter. Conversely, mid-latitude regions that normally would get the storms become drier because storms shift away.

This year, forecasters expect a fast transition to La Nina – likely by late summer. After a strong El Nino, like the world saw in late 2023 and early 2024, conditions tend to swing fairly quickly to La Nina. How long it will stick around is an open question. This cycle tends to swing from extreme to extreme every three to seven years on average, but while El Ninos tend to be short-lived, La Ninas can last two years or longer.