Scientists rely on research, statistical models, and climate forecast models to help them determine upcoming natural events.
Currently, scientists are have a difficult time deciding if and when the potential big El Niño event will happen. It will happen in 2017, but will it be the Summer or Fall?
"Right now, many climate forecast models do predict the development of a full-fledged El Niño during this summer or fall. It’s likely that these models are acting on the much warmer-than-average waters near the coast of South America—the “Coastal El Niño" says Anthony Barson in his NOAA climate.gov article entitled, "April 2017 ENSO update: Conflicting signals from the tropical Pacific Ocean."
Also, please check out the blog entitled, "Another El Niño heading our way?" written and posted by Dorian Janney.