text: The sun passes over the equator twice during the year, at the March and September equinoxes. As shown above in Figure 4-40, the sea surface temperatures in the western equatorial Pacific reach their maximums a few months later in May and November. The warm water is basically following the sun, with a lag, as it progresses between hemispheres. As Xiao and Mechoso (2008) describe, and to put it into terms of the data weve presented, the El Nio ebbs as the warm water passes from the western equatorial Pacific into the Southern Hemisphere.