The current El Nino weather phenomenon could be one of the strongest on record, according to the World Meteorological Organization (WMO).
The event occurs when the waters of the Pacific become exceptionally warm and distort weather patterns around the world.
Researchers say parts of the Pacific are likely to be 2C warmer than usual.
The WMO says that this year's event is strengthening and will peak by the end of this year.
The strongest El Nino on record was in 1997-98, but there were events that were significantly above the norm in 1972-73 and again ten years later in 1982-83.
Scientists say that the event now underway is sending sea temperatures in parts of the Pacific to levels not seen since the late 1990s.
In a statement the WMO said that this El Nino was gathering strength.
"Models and expert opinion suggest that surface water temperatures in the east-central tropical Pacific Ocean are likely to exceed 2C above average, potentially placing this El Nino event among the four strongest events since 1950," it said.
The WMO says that patterns of cloudiness and rainfall near the international dateline developed during the second quarter of this year and have been well maintained.