16 May 2012

GENEVA, 16 May 2012 (WMO) – The 2011-2012 La Niña has ended. La Niña conditions in the tropical Pacific transitioned to neutral (neither El Niño nor La Niña) conditions in early April 2012. Model forecasts and expert opinion suggest that neutral conditions are likely to continue into the Northern Hemisphere summer (austral winter). For the second half of 2012 a return of La Niña is unlikely, while neutral or El Niño conditions are currently considered to have equal chances of occurring. National Meteorological and Hydrological Services and other agencies will continue to monitor Pacific Basin conditions and outlooks to assess the most likely state of the climate during 2012.The weak to moderate strength La Niña of 2011-2012 ended in early April 2012, as tropical Pacific sea surface temperatures, sea level pressure and trade winds returned to neutral levels of ElNiño/Southern Oscillation (ENSO), with neither El Niño nor La Niña prevailing. The latest results from forecast models and expert opinion suggest that sea surface temperature anomalies will likely oscillate around neutral conditions into the northern summer (austral winter) of 2012. Beyond July 2012, however, some forecast uncertainty exists. Based largely on a recent build-up of heat in the deeper tropical Pacific Ocean, at least half of the dynamical climate models surveyed predict development of El Niño conditions during the July to September period. However, some dynamical models and more than half of the statistical models indicate neutral ENSO conditions will remain through 2012. Currently, practically none of the models suggests a return to La Niña conditions. Expert interpretation of these models and conditions suggests that while La Niña is unlikely to redevelop later this year, there is a greater than normal chance both for neutral conditions to continue and for the development of  El Niño during the second half of the year. >> Full text

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