> As I said in the other thread, it might be better to attempt continuous predictions of an El Niño index like NINO3.4. If one could get decent predictions of that at all times, not just during El Niño events, it would be much more convincing.
Yes, that would be very good. Note that since this index is defined in terms of sea surface temperatures, we can think of the challenge this way: use current sea surface temperatures to predict aspects of future sea surface temperatures. Of course there's no need to restrict ourselves to using current _sea surface temperatures_ - we could use the Dow Jones industrial average if that helped. But using just sea surface temperatures makes it into an interesting self-contained game: "how much do sea surface temperatures now know about future sea surface temperatures"?