Pictured: The most reasonable global SSTA outlook for JUL/AUG/SEP 2017 is provided by the International Research Institute for Climate and Society which indicates a weak El Nino ahead.
During MAR/APR 2017 the global atmosphere gained significant El Nino-like characteristics as identified by the multivariate ENSO index. The change in MEI rank from 31 in FEB/MAR 2017 (given the 1950-2017 climatology whereas 1 = strongest La Nina and 68 = strongest El Nino) to 58 in MAR/APR 2017 is the largest advance to an El Nino climate on record. The cause of the sudden advance was an El Nino-like climate signature in March related to an intense warming of the ocean off the northwest coast of South America followed by presence of Madden Julian oscillation convection across the entire eastern equatorial Pacific in April. The warm Nino12 SSTA lead to historic flooding of northwest South America while the MJO presence during April caused the U.S. pattern to gain heavy rain eliminating drought in the Mid-South U.S. Despite the El Nino-like events of the past 2 months certainly identified by the MEI observation 2 leading providers of ENSO forecasts, the Bureau of Meteorology/Australia and the NCEP CFS V2 (model) have backed off forecasting El Nino in 2017 after projecting at least moderate El Nino just 2 months ago. The Climate Impact Company assessment of these dizzying set of circumstances is typical of ENSO the past 2-3 years making ENSO phase prediction difficult. Likely contributing to the increased uncertainty is the widespread warming of the subtropical and eastern Pacific Ocean. The most likely scenario for mid-to-late summer in the northern hemisphere is that the widespread warming in the Pacific basin (now) will enable a weak El Nino to form.
