Long-term records of the sea surface temperature (SST) of the Indian Ocean are analyzed. During the last 50 years the Indian Ocean has shown a strong upward trend (1 C/century), most of which has occurred since 1976. Over the entire period, the Southern Oscillation Index (SOI) explains about 10% of the SST variance averaged over the entire Indian Ocean SST but higher (16%) over the central basin or 25% lagged by three months. Strong correlations are evident between the Arabian Sea SSTs and the All-India Rainfall Index (AIRI) which maximize 6 months
ahead of the summer monsoon (previous December) at about 0.5. A second large region of the Indian Ocean off Northwest Australia correlates well with the AIRI with similar lead times. In fact the strongest precursor is the sum of the Arabian Sea and Northwest Australian SSTs. This is referred to as the ASNWA SST index. These variations appear to be tied to the very strong biennial oscillation (Meehl, Yasunari). However, it is noted that there are large changes that occur around 1976 as initially discussed by Wang. For example, most of the basin wide warming has occurred since 1976. Whereas in the 1945-1998 data series the SOI correlates with Indian Ocean SST about the same, the biennial oscillation is far stronger in the 1945-1976 period, and the SST after 1976 correlates with the AIRI as high as .8 in the central Indian Ocean. The consequences of these statistical relationships to the prediction of climate variability to South Asia are discussed