The El Nino phenomenon, which is developing in the Pacific Ocean, could be the strongest recorded in modern history, warn experts from the British Meteorological Office.
El Nino occurs every two to seven years and usually lasts about a year. It causes ocean surface temperatures to rise and releases large amounts of heat into the atmosphere, affecting the weather in many parts of the world.
According to the latest forecasts, Pacific water temperatures could exceed 3 degrees above average this year.
If this happens, El Nino could be the strongest since the 19th century.
Experts warn that, combined with global warming caused by human activity, the phenomenon could make 2027 very likely to be the hottest year ever recorded.
The impacts of El Nino are already showing up in some regions.
In India, monsoon rainfall is below normal, while hurricane activity in the Atlantic is weaker.
In Australia, the risk of droughts and fires increases, while Peru, Ecuador and the southern US could face more flooding.
In Britain and northwestern Europe, the phenomenon could bring a wetter and stormier autumn.