La Niña is approaching: how it will influence the next hurricane season and what is expected for the southern hemisphere

La Niña is approaching: how it will influence the next hurricane season and what is expected for the southern hemisphere
La Niña is approaching: how it will influence the next hurricane season and what is expected for the southern hemisphere

This is what Mexico looks like during the passage of Cold Front 9 and a cold air mass. Photo: National Hurricane Center

One of the great contributors to the record global temperatures from last year, El Niño has almost disappearedand its opposite, The girl, is on the way.

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

La Niña and El Niño are both extremes of a recurring weather pattern that can affect the climate around the world.

Meteorologists know that La Niña has arrived when temperatures in the Eastern Pacific Ocean along the equator in western South America they cool down at least half a degree Celsius (0.9 Fahrenheit) below normal. During The boy, the same region it gets hot.

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

Meteorologists expect a rapid transition to La Niña, probably at the end of the northern hemisphere summer (EFE/Martin Alipaz/File)

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

Normally, air rises over the Amazon and Indonesia because the humidity of the tropical forests makes the air more buoyant there, and it descends in East africa and the Eastern Pacific. During La Niña, these loops intensify, generating stormier conditions in the places where they rise and drier conditions where they descend. During El Niño, ocean heat in the eastern Pacific changes those loops, so the eastern Pacific becomes stormier.

EL Niño and La Niña also affect the jet stream, a strong current of air that blows from west to east across the US and other mid-latitude regions. During El Niño, the jet stream tends to push storms into the subtropics, making these typically dry areas wetter. In contrast, mid-latitude regions that would normally experience storms become drier because the storms move away.

This year, meteorologists expect a rapid transition to La Niñaprobably late summer [del hemisferio norte]. After a strong El Niño, like the one the world experienced in late 2023 and early 2024, conditions tend to shift fairly quickly toward La Niña. How long it will last is an open question. This cycle tends to oscillate from extreme to extreme every three to seven years on averagebut while El Niño tends to be short-lived, La Niña can last two years or more.

This heat affects the atmosphere, causing more atmospheric movement over the Atlantic, fueling hurricanes (EFE/Orlando Barría)

Temperatures in the tropical Pacific also control the wind shear in much of the Atlantic Ocean.

Wind shear is a difference in speeds of the wind at different heights or directions. Hurricanes have a harder time maintaining their spine structure during strong wind shear because stronger winds aloft push the spine outward.

La Niña produces less wind shear, eliminating a deterrent to hurricanes. That’s not good news for people who live in hurricane-prone regions like Florida. In 2020, during the last La Niña, the Atlantic saw a record 30 tropical storms and 14 hurricanes, and in 2021 there were 21 tropical storms and seven hurricanes.

Forecasters are already warning that this year’s Atlantic storm season could rival 2021’s, due in large part to La Niña. He tropical Atlantic has also been exceptionally warm, with sea surface temperatures breaking records for more than a year. This heat affects the atmosphere, causing more atmospheric movement over the Atlantic, fueling hurricanes.

La Niña is bad enough for East Africa, where vulnerable communities are already in a long-term drought (Juan Pablo Zamora/Cuartoscuro.com)

The southwestern United States’ water supplies will likely be fine during the first year of La Niña due to all the rain last winter. But the second year tends to become problematic. A Third year, as the region saw in 2022, can cause serious water shortage.

Drier conditions also cause more extreme fire seasons in the west, particularly in the fall, when the winds intensify.

The impacts of El Niño and La Niña are almost a mirror image in the southern hemisphere. Chile and Argentina they tend to suffer droughts during La Niñawhile the same phase causes more rain in the Amazon. Australia suffered severe flooding during the last La Niña. La Niña also favors indian monsoon, which means above-average rainfall. However, the effects are not immediate. In South Asia, for example, changes tend to appear a few months after the official appearance of La Niña.

La Niña is bad enough for East Africa, where vulnerable communities are already in long-term drought.

The general trend is towards a warming of the world (EFE/ Daniel Sánchez)

El Niño and La Niña are now adding to the effects of global warming. That can exacerbate temperaturesas the world saw in 2023, and the precipitation they can overflow.

Since the summer of 2023, the world has had 10 consecutive months of record global temperatures. Much of that heat comes from the oceans, which are still at record temperatures.

La Niña should cool things down a bit, but the greenhouse gas emissions that drive global warming continue to rise in the background. So while fluctuations between El Niño and La Niña can cause short-term temperature changes, the general trend is towards a warming of the world.

*Pedro Di Nezio, Ph.D., is an associate professor of Atmospheric and Oceanic Sciences at the University of Colorado Boulder. He studies the dynamics, predictability and impacts of global climate fluctuations generated by tropical oceans, such as El Niño and La Niña.

*This article was published in The Conversation

 
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