A simple correlation analysis was used to investigate the linear relationships between sea surface temperature (SST) and monthly flow of Ganges and Brahmaputra at the borders of Bangladesh and India using approximately 50 years of river discharge data. Strong correlations were found between the equatorial Pacific SST and boreal summer Ganges discharge from three-month lag to two-month lead times. The El Nio-Southern Oscillation (ENSO) explains Ganges flow variance exceeding 0.95 significance level using both the Nino 3.4 SST correlation and the composites made for El Nio (La Nina) periods. The May SST of the southwest Pacific Ocean to the east of Australia continent has a strong correlation (>0.6) with early summer Ganges discharges. Using a lag correlation analysis of Ganges discharge and SST, we found a steady and continuous development in the Nino 3.4 SST relationship, and a strong correlation with the southwest Pacific SST which is most pronounced three-four months prior to the onset of Asian summer monsoon. These relationships mean that at least 25% of the interannual summer Ganges River discharge variability can be explained by antecedent equatorial and southwest Pacific SST. It provides a possible statistical method for linear forecasting two or three months in advance. The Brahmaputra River discharge, on the other hand, shows weak relationships with tropical SST variability except for the Bay of Bengal and the higher northern latitudes of the Pacific.