SOI (SOUTHERN OSCILLATION INDEX)

During the third quarter of 2004, the SOI has been moderately negative, with individual monthly index values of -0.7, -0.8, and -0.4, -0.3 during July, August, September, and October, respectively. Since January 2004, the average value of the SOI has been weakly negative, and since June 2004, the monthly values have been persistently negative. Nearly all El Niño events are associated with a persistently negative SOI near -1.0 or lower. During La Niña, the SOI is persistently positive, near +1.0 or higher. With weak El Niño conditions in the Pacific basin, the SOI should persist below zero for the next three to six months.