I have the same question as John.

The practical definition of "prediction" can be interpreted in different ways. I interpret as what John is saying is that we can treat this in either of two ways -- or both, for that matter:

1. Predict ENSO at the current time (or at historical times) based on correlated events from other measures, spatial or otherwise.

2. Predict ENSO at future times based on some sort of physical model or heuristic model that we can glean from past history.

We can use #1 to help with #2, but only if we have models for the other correlated measures. This is a subtle yet important detail. For example, we can find all sorts of correlations with rainfall, other indices such as NAO, AMO, etc., but unless we have models for those other measures, we can't use those to predict the future -- instead, we are simply chasing our tail and staying in the present.

Does that make sense as a reframing of the question ?