There is a strong chance that a weather pattern which can cause droughts and flooding will form this winter, meteorologists have said.
The last time El Nino occurred in 2015-16, it caused crop damage, fires and flash floods.
The event affected millions of people globally, including in Africa, Central America, Southeast Asia, and the Pacific islands.
There were drought conditions in Venezuela, Australia and a number of the Pacific islands.
Over the same period Uruguay, southern Brazil, and Paraguay experienced a lot of rain.
When El Nino happens, ocean surface temperatures warm up in the eastern and central Pacific.
The UN's World Meteorological Organisation (WMO) said there was a 75-80% chance of a new pattern forming by February.
It warned of potentially "significant" effects on "rainfall and temperature patterns", and important consequences for "agricultural and food security".
Its forecast is similar to another one released by the US government's national weather service earlier this month.
There is also a chance it could continue through the northern hemisphere winter of 2018-19, the WMO added.
More from United States
"The forecast El Nino is not expected to be as powerful as the event in 2015-2016, which was linked with droughts, flooding and coral bleaching in different parts of the world," said Maxx Dilley from the WMO.
"Even so, it can still significantly affect rainfall and temperature patterns in many regions, with important consequences to agricultural and food security sectors, and for management of water resources and public health, and it may combine with long-term climate change to boost 2019 global temperatures."