An atmospheric scientist explains what’s ahead for 2024.

Wild weather has been roiling North America for the past few months, thanks in part to a strong El Nino that sent temperatures surging in 2023. The climate phenomenon fed atmospheric rivers drenching the West Coast and contributed to summer’s extreme heat in the South and Midwest and fall’s wet storms across the East.

That strong El Nino is now starting to weaken and will likely be gone by late spring 2024.

So, what does that mean for the months ahead – and for the 2024 hurricane season?

What Is El Niño?

Let’s start with a quick look at what an El Nino is.

El Nino and its opposite, La Nina, are climate patterns that influence weather around the world. El Nino tends to raise global temperatures, as we saw in 2023, while La Nina events tend to be slightly cooler. The two result in global temperatures fluctuating above and below the warming trend set by climate change.

El Nino starts as warm water builds up along the equator in the eastern tropical Pacific Ocean, off South America.

A colored map shows temperature differences with a warm area just west of South America along the equator.
Reds and yellows show where Pacific waters were warmer in 2024 than in 2022. The abnormally warmer region along the equator is what we call El Nino. Weak El Nino events occur every few years, with strong events like this averaging once every 10 to 20 years. (Courtersy: NOAA)

Typically, tropical Pacific winds blow from the east, exposing cold water along the equator and building up warm water in the western Pacific. Every three to seven years or so, however, these winds relax or turn to blow from the west. When that happens, warm water rushes to the east. The warmer-than-normal water drives more rainfall and alters winds around the world. This is El Nino.

The water stays warm for several months until, ultimately, it cools or is driven away from the equator by the return of the trade winds.

When the eastern Pacific region along the equator becomes abnormally cold, La Nina has emerged, and global weather patterns change again.

What To Expect From El Nino In 2024

While the 2023-24 El Nino event likely peaked in December, it is still strong.

For the rest of winter, forecasts suggest that strong El Nino conditions will likely continue to favor unusual warmth in Canada and the northern United States and occasional stormy conditions across the southern states.

Two maps of typical winter conditions under El Nino and La Nina show the Southwest wetter and the Northwest and upper Midwest generally warmer under El Nino.
Typical winters under El Nino and La Nina show the striking differences between the two patterns. Not all El Niños turn out this way. (Courtesy: NOAA Climate.gov)

El Nino is likely to end in late spring or early summer, shifting briefly to neutral. There’s a good chance we will see La Nina conditions this fall. But forecasting when that happens and what comes next is harder.

How An El Nino Ends

While it’s easy to tell when an El Nino event reaches its peak, predicting when one will end depends on how the wind blows, and everyday weather affects the winds.

The warm area of surface water that defines El Nino typically becomes more shallow toward spring. In mid-May 1998, at the end of an even stronger El Nino event, there was a time when people fishing in the warm surface water in the eastern tropical Pacific could have touched the cold water layer a few feet below by just jumping in. At that point, it took only a moderate breeze to pull the cold water to the surface, ending the El Nino event.

But exactly when a strong El Nino event reverses varies. A big 1983 El Nino didn’t end until July. And the El Nino in 1987 retreated into the central Pacific but did not fully reverse until December.

As of early February 2024, strong westerly winds were driving warm water from west to east across the equatorial Pacific.

These winds tend to make El Nino last a little longer. However, they’re also likely to drive what little warm water remains along the equator out of the tropics, up and down the coasts of the Americas. The more warm water that is expelled, the greater the chances of full reversal to La Nina conditions in the fall.

Summer And The Hurricane Risk

Among the more important El Nino effects is its tendency to reduce Atlantic hurricane activity.

El Nino’s Pacific Ocean heat affects upper level winds that blow across the Gulf of Mexico and the tropical Atlantic Ocean. That increases wind shear – the change in wind speed and direction with height – which can tear hurricanes apart.

The 2024 hurricane season likely won’t have El Nino around to help weaken storms. But that doesn’t necessarily mean an active season.

During the 2023 Atlantic hurricane season, El Nino’s effect on the winds was more than offset by abnormally warm Atlantic waters, which fuel hurricanes. The season ended with more storms than average.

The Strange El Nino Of 2023-24

Although the 2023-24 El Nino event wasn’t the strongest in recent decades, many aspects of it have been unusual.

It followed three years of La Nina conditions, which is unusually long. It also emerged quickly, from March to May 2023. The combination led to weather extremes unseen since perhaps the 1870s.

La Nina cools the tropics but stores warm water in the western Pacific. It also warms the middle latitude oceans by weakening the winds and allowing more sunshine through. After three years of La Nina, the rapid emergence of El Nino helped make the Earth’s surface warmer than in any recent year.

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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