When sea-surface temperatures across the equatorial Pacific Ocean measure 0.5C above average for any particular 3-month period–as they did this year for April, May, and June–it heralds the onset of the worldwide weather maker known as El Nio.
Early this year, an increase in ocean temperatures in the central Pacific led researchers at the National Oceanic and Atmospheric Administration (NOAA) to suggest that an El Nio was on the way. Around the same time, NASA scientists analyzed patterns of wind and rainfall southeast of India and predicted an El Nio would appear between July and October (SN: 3/2/02, p. 142: El Niño's coming! Is that so bad?). From temperature data collected by satellites, buoys, and ships, NOAA made it official on
July 11: The agency announced that the latest El Nio had indeed arrived.