Last night saw heavy rains in Chennai over the southern suburbs and OMR areas with Hindustan University in Kelambakkam recording 74 mm till early morning 4:30 AM. Places to the south of Tambaram like Maraimalai Nagar, Kaattangulathur, Chengalpattu also got these spells of heavy rains. While the south suburbs enjoyed the rains in Chennai the rest of the city had to live with only hearing the distant thunderstorms and possibly a marginal reduction in temperatures compared to yesterday. 
As one can observe from the chart the rains in Chennai were pretty much confined to the suburbs south of the city with Poonamallee the only exception to record 3 mm rains with the rest of the city completely missing the rains.
Things are looking good for the rains to continue today as well over Coastal Tamil Nadu thanks to a combination of factors that is likely to work in tandem. The development of a fresh Upper Air Cyclonic Circulation over Bay is expected to create an pseudo LWD conditions over Peninsular India at Mid Tropospheric Level providing for the necessary atmospheric instability in the region.
Along with the wind aided instability models indicate a very high potential available for Convective Energy as well around North Tamil Nadu and adjoining parts of South AP & Karnataka which is likely to intensify the thunderstorms in the region. This could result in one or two places in Coastal Tamil Nadu to get heavy spells of rains. In particular there is a fair chance of places around Pondicherry to get isolated heavy rains.
Parts of Chennai also could be in line for the spells of rains though the best spells of rains will once again be to our South possibly thanks to the winds from the Northwest. Nevertheless today also we are likely to see overnight thunderstorms bring rains in Chennai with a decent chance for most areas to benefit from these rains.