The World Meteorological Organisation (WMO) said its modelling suggested a "fairly large potential for an El Nino, most likely by the end of the second quarter of 2014."
"If an El Nino event develops, it will influence temperatures and precipitation and contribute to droughts or heavy rainfall in different regions of the world," WMO chief Michel Jarraud said in a statement.
The El Nino phenomenon occurs every two to seven years, when the prevailing trade winds that circulate surface water in the tropical Pacific start to weaken.
"While there is no guarantee this situation will lead to an El Nino event, the longer the trade winds remain weakened, and sub-surface temperatures stay significantly warmer than average, the higher the likelihood," it said.
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Two thirds of climate models predicted that the phenomenon would begin sometime between June and August, with a few suggesting it could start as early as May, and the remainder predicting no El Nino this year, it said.
It is often followed by a return swing of the pendulum with La Nina, which is characterised by unusually cool ocean surface temperatures in the central and eastern tropical Pacific.
Scientists, who closely monitor the two climate patterns, say that while they are not caused by climate change, rising ocean temperatures caused by global warming may affect their intensity and frequency.
"El Nino has an important warming effect on global average temperatures," Jarraud cautioned, stressing that combined with human-induced warming from greenhouse gases such events had "the potential to cause a dramatic rise in global mean temperature.