Presented at the 2018 AGU Fall MeetingThe critical dependence of the food production and agrarian economy on rainfall makes the linkage of the oceanic and terrestrial water balances through monsoon of paramount importance to many countries in South Asia. We found that the onset of summer monsoon is always preceded by sea surface temperature (SST) rises above deep convection threshold (approximately 27°C) in both the Bay of Bengal and the Arabian Sea. It has been postulated that, during boreal summer, intraseasonal oscillation systems propagate eastward in equatorial Indian ocean and then organized convections move northward into the embayments, following the warm water, and trigger the southwest monsoon. We found that surface heating, which is high throughout the pre-monsoon dry season, is not the main cause of the SST spike. The SST rise corresponds to a shallowing of the ocean mixed layer, indicating ocean stratification change associated with salinity advection between the two embayments. Surface salinity measurements by spacebased sensors at sufficient resolutions (e.g., Soil Moisture Active and Passive SMAP), are used to reveal not only the change of seasonal salinity advection driven by river discharges but mesoscale responses to monsoon rain. The monsoon rain effect on the water balance in the subcontinent are examined through mass changes measured by Gravity Recovery and Climate Experiment (GRACE ), the river discharges estimated from radar altimeters, and the integrated moisture advection across the coastline that we produced from satellite data.