In a day of possible close miss for Chennai Rains, models are expecting a stormy evening for most parts of North Tamil Nadu. With the Westerly winds firmly established now over Peninsular India it is time for various atmospheric instabilities to come into place to trigger likely thunderstorms over the region. Prediction of summer thunderstorms are always a case of “Fraught with Risk” thanks to a larger number of unknowns for the models as well. The evolution of summer thunderstorms owe a lot to local conditions which more often than not does not get accurately reflected in Numerical Model Outputs resulting in sometimes exaggeration or under estimation of these thunderstorms in general. 
Temperatures are likely to be higher than the last couple of days across the Peninsular region. In particular we could see possible low 40s from one or two places in Tiruvallur, Kanchipuram & Vellore districts. Unlike the last two days or so when Tamil Nadu did not see many places record 40 degrees we could see a few places today creep above 40 degrees as temperatures are set to increase under slightly more clearer skies during the early part of the day.
As one can see we are likely to see fairly stormy evening for many parts of North & West Interior Tamil Nadu with one or two places in Vellore, Tiruvallur, Dharmapuri, Salem & Krishnagiri districts likely to see fairly intense spell of summer rains. These thunderstorms are likely to be aided by heat induced convection along with atmospheric instability in the form of good CAPE values available in the region. We are likely to see Sea Breeze set in around 2 PM over the North Coastal Tamil Nadu which is likely to trigger some of these thunderstorms in Tiruvallur district.
While models are expecting rains for many parts of North Tamil Nadu the prospect of Chennai Rains will primarily depend on the movement of these thunderstorms from the interiors to the sea. The exact path is difficult to predict as the wind patterns evolve as the thunderstorms mature. But as things stand we are likely to see a scenario of possible rains for Western & Southern Suburbs of Chennai while the city could possibly miss out. There is some chance of the rains pushing in as close as Avadi / Ambattur to the West and parts of Tambaram getting a shower or two. Chennai Rains A case of so near yet so far
All in all it looks like most places of Tamil Nadu has a chance of some rains today with the best chance present in places around Vellore & Krishnagiri.