The Pacific weather phenomenon known as La Nina emerged in August and will likely operate into early next year, prolonging the drought in the Horn of Africa, the U.N. weather agency said Thursday.
La Nina, which is characterized by cooler sea surface temperatures in the central and eastern tropical Pacific, normally triggers some extreme weather patterns, such as flooding in Australia and drought in Texas. It is the opposite of El Nino, a warming of surface ocean temperatures in the eastern Pacific.
The World Meteorological Organization said the 2011 drought in Somalia and northern Kenya has been "exacerbated by La Nina's influence."
"Its impact is not uniform, and some parts of the Greater Horn of Africa receive greater than normal rainfall during La Nina episodes," WMO said.
La Nina conditions are also associated with greater rainfall in the southern Pacific and southern African countries, and dry conditions in parts of east Africa, southwest Asia and the southern United States.
This year's La Nina conditions could strengthen to "moderate intensity," the Geneva-based agency said, but added it is expected to be considerably weaker than the most recent La Nina episodes, which have been linked to flooding and drought.
North America will be affected by a less predictable weather pattern known as the Arctic oscillation. That expansion and contraction of cold air over the North Pole "could produce dramatic short-term swings in temperatures this winter," the agency said.