I remember meeting with my supervisor and having a casual discussion about a statement NOAA made about an expected El Niño this year. We both found it funny how strong the language was worded but in fact, we couldn't say they were wrong or right but the numbers did seem plausible.
An El Niño is an extremely difficult phenomenon to model as it is influenced by an array of factors, each of which we do not fully understand. Thus, by the laws of chaos, that translates to models partly getting it right while fully waiting with fingers crossed. Just goes to show that a model is exactly what the name implies, an estimate and perhaps we may never be able to fully squeeze nature and all her mysteries through a climate model.
Regardless of the precise outcome, some experts note that the recent shift in forecasts should be a reminder that there's still a lot about El Niño events we still don't know — particularly how, exactly, these events are triggered.