The World Meteorological Organization is forecasting a possible return of the El Niño phenomenon to the Pacific Ocean later this year, hot on the heels of the 2015-2016 back-to-back El Niño events, with only a short-lived, milquetoast La Niña cooling period having occurred in between.

The WMO, drawing on recent observations, climate models and historical trends, predicts that there is a 50-60 percent chance of a reoccurrence of El Niño before 2017 ends. Regional El Niño-associated warming in the Eastern Pacific has already caused heavy rains in Peru and Ecuador, leading to extensive flooding. The sea surface temperatures in the far eastern tropical Pacific have been 2ºC above normal during February and March.

"Memories are still fresh of the powerful 2015-2016 El Niño which was associated with droughts, flooding and coral bleaching in different parts of the world and which, combined with long-term climate change, led to the increase of global temperatures to new record highs in both 2015 and 2016," says Maxx Dilley, the WMO’s climate prediction and adaptation division lead.

Such a sudden return for an El Niño is extremely unusual, as the typical interval between occurrences is two to seven years. "Normally we would expect a longer interval before another warming. But, having said that, El Niño variability is really rather irregular," explains Tim Stockdale, from the European Centre for Medium-range Weather Forecasts (ECMWF).