The vertical structure and dynamics of deep convective clouds plays an important role during the Indian summer monsoon period. The characteristics of deep convective cells (DCC) and their microphysics remain unclear, especially during the onset phase of the monsoon. Further, the intensity of convection is an important element, which plays a key role in the progression of the monsoon. Thus the present study focuses on characterizing DCC over a coastal location Thumba (8.50 N, 770E) during the onset of the Indian summer monsoon periods of 2017, 2018 and 2019 using C-band polarimetric Doppler Weather Radar (DWR) measurements in terms of their intensity, vertical extent, top heights and their microphysical properties. A method is devised to identify the DCC from the DWR observed reflectivity cross-sections. The results showed that the occurrence of reflectivities in the range of 30-40 dBZ dominates below 6 km and the reflectivities in the range of 10-20 dBZ dominates above 6 km. The diurnal evolution of DCC also been investigated and it is found that these systems peak at three local time intervals viz., 5-7, 11-14 and 16-19 hrs during the study period. The present results provide a quantitative assessment of DCC including their diurnal evolution during the onset of Indian summer monsoon season over Thumba using DWR observations for the first time.