Recently, several studies have looked at SST warming in the southwestern Indian Ocean and the eastern Pacific, and have found that there is a significant correlation between anomalous warming in the Indian Ocean and El Niņo (see figure below), although SST signals in the eastern Pacific are much larger. These studies (Tourre and White, 1995 and Nicholson, 1997) have found correlations between the Indian Ocean and the Pacific for almost every El Niņo back to 1946. I have looked at the T/P altimeter data and see a similar correlation, but the extreme sea-level values are closer to the same magnitude (see below).
SST data averaged over southwestern Indian Ocean and eastern equatorial Pacific. The scale for Pacific SST anomalies is on the left hand side; the scale for Indian Ocean SST anomalies is on the right.
T/P sea-level anomalies averaged over the same region.