No two El Niños are alike, but the disruption is felt most sharply in the tropics.
Flooding is common in northern Peru and southern Ecuador, and can reach parts of East Africa, Central Asia and the southern United States.
At the same time, the risk of drought and wildfire rises across much of Australia, Indonesia and northern South America – hitting agriculture and global food stocks.
El Niño also tends to suppress Atlantic hurricanes, and forecasters already expect a quieter-than-average season.
“While that sounds like a good thing, for Central America that leads to a lot less rainfall and potentially drought conditions,” said Liz Stephens, professor of climate risk and resilience at the University of Reading.
Even the UK feels it, if faintly: El Niño can tilt the odds towards a mild start and cold end to winter, though the links are loose.
For many, the forecast is far from abstract.
“An El Niño declaration is not just another weather forecast – for millions of people it is a deadly siren to be feared,” said Mohamed Adow, director of campaign group Power Shift Africa.
“It means failed rains, dying crops, rising food prices, and families pushed to the edge yet again. In East Africa especially, this will land on communities already battered by droughts and floods in recent years.”
Japan’s Meteorological Agency (JMA) takes a similar view to NOAA, judging that El Niño conditions are present. It adds it is all but certain to last into the autumn.
Not every agency is ready to call it, though. Australia’s Bureau of Meteorology (BoM) uses a stricter criterion, requiring sea surface temperatures to exceed 0.8C above average.
This week it said the tropical Pacific was “approaching El Niño conditions”, with central Pacific temperatures already crossing its thresholds, but it stopped short of formally declaring the event had begun.
It expects El Niño to develop later this year, and says it could be strong.
El Niño occurs every two to seven years and usually lasts about a year.
There is still no conclusive proof that climate change is making these events stronger or more frequent – but a warming world can supercharge their effects.
Additional reporting by Erwan Rivault
