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STORY: After three years dominated by the cooler La Nina weather pattern... El Nino is now underway, according to a U.S. climate monitoring agency.

The last time a strong El Nino was in full swing was 2016...

when the world saw its hottest year on record.

And scientists say this year looks particularly worrying.

[NOAA CLIMATE SCIENTIST, TOM DI LIBERTO]

“El Nino could lead to 2024 being one for the record books.”

El Nino is a natural climate pattern borne out of unusually warm waters in the eastern Pacific... though scientists are not entirely sure what kicks off the cycle.

It's likely to yield extreme weather later this year - from tropical cyclones - to heavy rainfall.

Tom Di Liberto is a climate scientist with the U.S. National Oceanic and Atmospheric Administration.

"El Nino is not like a storm. El Nino is not going to hit you on Tuesday. El Nino is all about changing the kind of patterns that weather plays in. So, when we talk about a moderate or strong event, that's basically saying that El Nino has a stronger influence on creating the atmospheric patterns that might stay around a while for a period of time.”

During an El Nino the southern U.S. sees cooler and wetter weather, while parts of the U.S. West and Canada are warmer and drier.

Hurricane activity usually falters in the Atlantic... but in the Pacific, tropical cyclones get a boost.

Australia usually endures extreme heat, drought and bushfires.

Parts of Central and South America may experience heavy rainfall.

The Horn of Africa could see a reprieve after five consecutive failed rainy seasons.

Weather anomalies can be more extreme depending on where waters are warmest, making things drier or wetter in certain regions.

“...the Atlantic is very, very warm. The Western Pacific is pretty warm. The Indian Ocean is really warm. So that in and of itself, even if there wasn't an El Nino, would mean that there's an increased risk for coral bleaching in tons of different places around the globe.”

There's also concern that global sea surface temperatures could supercharge extreme weather.

During the last El Nino, anchovy stocks off Peru’s coast crashed and nearly a third of the corals on Australia’s Great Barrier Reef died.

While climate change is doubling down on the impacts from El Nino, whether climate change influences the phenomenon itself is less clear.

“Most of the warmest years on record that we've seen in the past have happened due to the influence of El Nino, because it gives that little bit extra push on to the global temperatures on top of the warming that we're already causing due to human caused climate change.”