Scientists around the world are warning a strong El Niño this year, colloquially dubbed a super El Niño, could lead to extreme weather events — from heavy rainfall to exacerbated droughts.
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The National Oceanic and Atmospheric Administration predicted last month there's an 82% chance of El Niño emerging between May and July. The United Nation's World Meteorological Organization agrees, saying there's a 90% chance El Niño will continue until at least November.
"The world must treat it as the urgent climate warning it is," said U.N. Secretary-General António Guterres in a video statement. "El Niño conditions will pour fuel on the fire of a warming world. Impacts will hit even harder, travel even further and cross borders with devastating speed."
The last El Niño event happened in 2023 and 2024 and "was one of the five strongest on record," according to World Meteorological Organization Secretary-General Celeste Saulo.
Those years were marked by record high global temperatures, severe droughts and intense cyclones.
Here's what to know about the weather phenomenon.
What is El Niño?
Trade winds usually push warm water in the Pacific Ocean from South America to Asia. During El Niño, the trade winds are weaker and the Pacific's warm water moves toward the Americas instead.
El Niño is "the warm phase of a natural seesaw in the equatorial Pacific sea surface temperatures," said Robert Burgman, an atmospheric science professor at Florida International University.
South American fishermen in the 1600s gave the weather pattern its name: El Niño, "the little boy" in Spanish, was a reference to baby Jesus. Every few years, the fishermen noticed warm waters around Christmas time.
There's also an opposing weather pattern known as La Niña. Strong trade winds push more warm water to Asia while pushing even colder water to the Pacific coast of the Americas.
What happens during El Niño?
El Niño events tend to last for several months. They make "normally dry places wet and normally wet places dry," said Paul Roundy, professor of atmospheric and environmental sciences at the State University of New York at Albany.
The weather pattern usually takes place every few years and tends to intensify in the fall, peaking in the winter, said Bob Henson, a meteorologist and journalist with Yale Climate Connections.
In the U.S., El Niño's effects are often divided between the North and South. From fall to spring, the southern U.S. can see increased rain which can lead to flooding. In the north, winters can be warmer and drier.
A worker wades through a flooded freeway after an El Niño-strengthened storm brought rain to Los Angeles, California, Jan. 6, 2016. Photo by Lucy Nicholson/Reuters
The U.S. could see heat waves across the country, especially in the North, flooding in the South and wildfire risk in the Eastern and Northern Rockies, said Erin Coughlan de Perez, a climate scientist and professor at Tufts University.
Internationally, there could be droughts and risks of fire across Indonesia, Australia, parts of the Amazon and Southern Africa, and more rain in parts of South America and East Africa, Burgman said.
READ MORE: Southern Africa facing its worst hunger crisis in decades due to El Niño, the UN says
However, the full extent of El Niño's effects aren't always known, said climate scientist Tom DiLiberto, media director for Climate Central, a nonprofit news organization covering climate change.
El Niño isn't the only weather pattern taking place at any given time — other phenomena can worsen or mitigate the effects of El Niño — but El Niño is the only phenomena scientists are able to predict months in advance, he said.
"The plus side here, if there's any plus side, is that with an El Niño being forecast, we can begin to prepare now for some of these impacts that might happen later in the year," DiLiberto said. "In any given year, there are going to be climate extremes around the world. During an El Niño year, at least we have an idea of where they might happen months ahead of time."
What is a super El Niño and will that happen?
The term "super El Niño" isn't officially recognized by scientists, but is commonly used to describe a strong El Niño, Henson said.
To gauge how strong an El Niño will be, NOAA tracks the Pacific Ocean's surface temperature and classifies the event into four categories: weak, moderate, strong or very strong.
This year, forecasts generally project El Niño to be strong or very strong.
"That doesn't necessarily translate into, when it rains, it's going to pour," DiLiberto said. "But what it does tend to do is lead to there being more consistent impacts across the United States and elsewhere around the world."
Burgman said even a moderate El Niño could lead to record-breaking global temperatures as a result of temperatures already warming due to climate change.
What can past super El Niños teach us?
Roundy said several forecasting models show the possibility that this year's El Niño may be the strongest one since the 1870s.
"The strongest event recorded is not guaranteed, but a strong event is quite likely," he said.
A super El Niño in 1877 and 1878 led to massive droughts and widespread famine that killed millions of people.
"However, modern agriculture and food distribution systems are much better today," Roundy said. "China has water storage in reservoirs and India has over 90 million metric tons of grain stored."
DiLiberto pointed to more recent strong El Niño events for a look at what could happen this year. There were warm winters and severe flooding in the U.S. in 1997 and 1998. And during the El Niño in 2015 and 2016, there was a 500-year drought in the Caribbean.
But the outcome of a super El Niño can't be entirely predicted.
"The 1997 to '98 super El Niño brought devastating California flooding, while 2015 to '16 largely missed the state," Burgman said. "So even within the 'super' category, the regional outcome is far from certain."
Like previous El Niños, the upcoming one "could have really big, profound impacts on communities," DiLiberto said. "That's especially true for areas around the world that are more susceptible to slight changes causing really drastic impacts."
Coughlan de Perez said this year's El Niño could look different from previous El Niños because of the world's "precarious state."
Disruptions to energy supply chains by the wars in Iran and Ukraine could be further exacerbated by extreme weather events.
This year's El Niño "will add to food shortages worldwide," said Mark Cane, an oceanographer at Columbia University. "Getting fertilizer through the Strait of Hormuz would help."
The crucial shipping route has largely been closed since the U.S. launched the war in Iran.
A pedestrian pier closed by authorities due to high surf from an El Niño-strengthened storm is pictured in Ocean Beach, California, Jan. 7, 2016. Photo by Mike Blake/Reuters
What does an El Niño forecast mean for hurricane season?
An El Niño generally indicates a quieter hurricane season in the Atlantic and a more active season in the Pacific Coast.
WATCH: NOAA forecasts milder Atlantic hurricane season thanks to El Nino
NOAA's forecast for this year's hurricane season reflects that. The agency predicted a 55% chance of a below-average season with a total of eight to 14 named storms in the Atlantic Ocean, Caribbean Sea and Gulf of Mexico. Meanwhile, the National Hurricane Center announced the season's first tropical storm, Amanda, in the Pacific Ocean this week.
However, climate scientists told PBS News that people shouldn't let down their guard.
"Prepare for hurricanes like you always should. The odds tilt favorable, but odds aren't how we make plans," Burgman said.
Experts said dangerous hurricanes can develop during El Niño, and it only takes one storm to cause major damage.
Hurricane Andrew, a Category 5 storm, killed 65 people in 1992 during a moderate to strong El Niño.
"So fewer storms on the board does not mean you skip the evacuation plan or let the insurance lapse," Burgman said.