Rob Painting at Skeptical Science has a technical post on the El Niño predicted for later this year. The description is slightly different than ones I have seen elsewhere and adds information from an Australian perspective (or at least in addition to the North American one). It includes some good description of the mechanics of water and air flows around the equator. Regardless, it is an interesting complement to the NOAA-CPC and WunderBlog posts mentioned earlier.
On a side note, I have been noticing many different websites posting on the El Niño forecast alert. I am not going to link to all of them as they seem to regurgitate the same info from the same sources. But, it is a situation that is gaining attention.