El Nino occurs every 2-7 years, bringing radical changes in climate Geneva – Arabstoday The El Nino and La Nina climate patterns are unlikely to make an appearance during the first half of this year, the United Nations’ weather agency said on Monday. "Model forecasts and expert opinion suggests that the likelihood of El Nino or La Nina conditions developing during the first half of 2013 is low," the World Meteorological Organisation (WMO) said in a statement.
During the past 10 months, indicators in the tropical Pacific, including ocean temperatures, sea level pressure and cloudiness, "have generally been at neutral levels, indicating that neither El Nino nor La Nina conditions have been present," it added.
The phenomena are significant factors in the fluctuations of the world climate.
El Nino occurs every two to seven years, when the trade winds that circulate surface water in the tropical Pacific start to weaken.
A mass of warm water builds in the western Pacific and eventually rides over to the eastern side of the ocean.
The outcome is a major shift in rainfall, bringing floods and mudslides to usually arid countries in western South America and drought in the western Pacific, as well as a change in nutrient-rich ocean currents that lure fish.
It last occurred from June 2009 to May 2010.
El Nino 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, and which was last declared over in April 2012.
The two climate patterns are closely watched by scientists, who say that while they are not caused by climate change, rising ocean temperatures caused by global warming may affect their intensity and frequency.