Yosef Ashkenazy

A warm tongue of water stretches along the equatorial Pacific, and within weeks, Peru sees torrential rains while Australia's pastures dry out. That is how El Niño begins: a natural conductor that, at critical moments, makes only a few orchestra members play, but much louder.

An orchestra falls out of tune before a storm, then plays in unison again. In the equatorial Pacific, within a rectangle stretching from 5°S to 5°N and from 120°W to 170°W, water temperatures usually change in concert, like musicians playing the same part. This area is called the Niño 3.4 region.