As an Indian component of the International Tropical Ocean Global Atmosphere (TOGA) program, the National Institute of Oceanography, Goa, has initiated a long-term observational program during 1990 with financial support from the Department of Science and Technology. The main objective of the program is routine monitoring of the upper ocean thermal structure along selected shipping lanes in the seas around India on annual and interannual time scales. Utilizing the near bi-monthly XBT data along Chennai-Andamans section collected using ships of opportunity during 1991-96, spatio temporal variability of upper layer thermal fields is examined on annual and interannual time scales. The observed variability is supported with two independent data sets: (1) Renold's weekly SSTs, and (2) TOPEX altimeter sea-level anomalies. During the observational period a few events were captured to examine thermal response of the upper ocean to varying storm forcing. Special CTD cruises were conducted to supplement the XBT data and identified the presence of Arabian Sea origin high salinity waters at sub-surface depths in the central Bay of Bengal during south-west monsoon season. Further, an improved temperature climatology for the Bay of Bengal is developed by compiling all the available temperature profiles, which outnumbered (doubled) the temperature data used in the best known Levitus and Boyer (1994) temperature climatology. Distribution maps of Levitus and Boyer climatology revealed several artifacts when compared with new climatology. In addition, with the help of new temperature climatology, detected long baroclinic Rossby waves