GENEVA (AP) — There's a strong chance an El Nino weather event will reappear before the end of the year and shake up climate patterns worldwide, the U.N. weather agency said Thursday.

The El Nino, a flow of unusually warm surface waters from the Pacific Ocean toward and along the western coast of South America, changes rain and temperature patterns around the world and usually raises global temperatures.

An update Thursday from the Geneva-based World Meteorological Organization puts the odds of El Nino at 60 percent between June and August, rising to 75-80 percent between October and December. It said the expected warming would come on top of the effects of man-made global warming.

"El Nino leads to extreme events and has a pronounced warming effect," said WMO Secretary-General Michel Jarraud. "It is too early to assess the precise impact on global temperatures in 2014, but we expect the long-term warming trend to continue as a result of rising greenhouse gas concentrations."

The outlook is for El Nino to reach peak strength during the last quarter of the year and into the first few months of 2015 before dissipating.

Tropical Pacific Ocean temperatures have already warmed to weak El Nino levels, but the weather event hasn't fully established itself yet based on readings of other conditions such as sea level pressure, cloudiness and trade winds, the report said.

Rupa Kumar Kolli, chief of a WMO division that deals with climate prediction and adaptation, said the El Nino would likely have moderate strength, but there remains a wide range of possibilities.

"We are expecting about the same levels" as the last El Nino from 2009 to 2010, which was the hottest year on record, he said.