The outlook for El Niño has become particularly difficult because of conflicting signals. Columbia University’s International Research Institute for Climate and Society reports that computer models are predicting a strong El Niño, in particular because of the above average sea surface temperatures (SSTs) in the eastern tropical Pacific, or what has become known as a coastal El Niño. The following image indicates the extreme variance from the 1981 – 2010 average in the waters along the coast of Ecuador and northern Peru which have experienced exceptionally heavy rains recently.
The following image (Ken Takahashi – Instituto Geofisico del Peru) shows this north western part of South America in more detail. It will be noted how the cold Humboldt current which normally affects coastal water temperatures as far north as Ecuador, and is instrumental in making the Atacama desert one of the driest regions on earth, by March 2017 was failing to influence northern Peru SSTs.
On the other hand the earlier image shows central Pacific SSTs are below average, more like La Niña than El Niño. A typical El Niño Southern Oscillation (ENSO event) spans the width of the Pacific. Statistical models based on previous events are coming up with much lower probabilities of a strong El Niño than dynamical models. In particular there is an absence of the coupled behaviour of ocean and atmosphere that normally accompanies El Niños – a weakening of the westward blowing trade winds at the surface accompanying the higher SSTs of the eastern Pacific. Also such a quick succession of El Niño then La Niña followed by another El Niño has not occurred in the last 50 years. Typically there is quite a long period of neutral SSTs preceding an El Niño. Hence the considerable difference between the dynamically modelled probabilities of an El Niño and those tempered by human intervention, mentioned in a recent blog on Southern African climate.