Indonesia experienced widespread drought caused by El Niño in 2015
The El Niño event that is developing over the Pacific Ocean is likely to be the strongest in living memory, the Met Office has warned.
The powerful natural climate phenomenon pushes up global temperatures and can increase the risks of extreme weather.
Added to the effects of human-induced climate change, the Met Office is warning that it is "very likely" to mean 2027 is the hottest year on record.
There is growing evidence that weather patterns around the world are already being affected, with below-average monsoon rains in India and suppressed hurricane activity in the Atlantic Ocean.
El Niño could put the UK at greater risk of a wet, stormy autumn.
"We should be clear that this is an unprecedented event", said Prof Adam Scaife, head of long-range forecasting at the UK Met Office.
"I have never seen an El Niño signal this intense in our forecasts."
El Niño is a naturally occurring weather pattern, which happens about every two to seven years, lasting for around a year.
Trade winds that typically blow from east to west across the Pacific Ocean can weaken or even reverse, allowing warm water to spread eastwards.
Heat is released from the ocean into the atmosphere, lifting global temperatures and shifting rainfall patterns.
Scientists declare an El Niño when sea surface temperatures in a key area of the Pacific are 0.5C or more above average.
Current measurements show that they are well over 2C above normal.
Latest forecasts from the Met Office suggest that these temperature anomalies could exceed 3C later this year as El Niño nears its peak.
This would be unprecedented in records going back to 1950, and probably the strongest event since the 19th century.