In a change in fortunes particularly North Tamil Nadu Heat Wave conditions are likely to prevail in the region with the temperatures that have been rising steadily over the last couple of days set to shoot up another notch today. Yesterday saw both observatories of Chennai record temperatures in excess of 39 degrees while Tiruttani was the hottest place in Tamil Nadu scorching to about 41 degrees.
To put things in perspective on how the Tropical Disturbance that finally evolved in Cyclone Roanu affected the weather pattern over East Coast of Tamil Nadu a glance at the temperature anomaly chart will reveal the incidental benefit. While most of us are aware of the rainfall that was recorded in the region as the Depression moved along the coast it played a huge role in also moderating the temperature patterns for a few days as well.
The other effect of Cyclone Roanu has been the change in wind directions. What was predominantly Easterly winds till a week back has now changed to Westerly winds under the influence of Cyclone Roanu. Bay of Bengal normally hosts a Tropical Disturbance in Summer to get the seasonal wind change effected from East to West to herald the Southwest Monsoon Season. With Cyclone Roanu that seasonal change of wind has been effected. We will now start to see the real summer of Chennai aided by the Westerly winds.
Coming to today’s weather conditions one of the key factors that is likely to aggravate the situation is Lack of Cloud Cover. As one can observe from this weather chart for today afternoon areas around Chennai are likely to see very clear skies with pretty much no cloud cover what so ever. This clear skies will allow the radiation of direct heat increasing the discomfort factor.
Particularly in North Tamil Nadu Heat Wave conditions are likely to be seen due to the combined conditions of clear skies and predominantly West / Northwest Winds which is likely to increase the Ground Heat Radiation making it a heady concoction of heat during the day. 
Places around Kanchipuram, Arakkonam, Tiruttani & Tiruvallur etc are likely to see temperatures cross 42 degrees and is likely one or two places in this region could even record 43°C possibly. Similarly the western suburbs of Chennai is likely to see extreme conditions with places like Avadi etc likely to record day time max temperature of around 41 / 42°C.
All in all it is going to be a North Tamil Nadu Heat Wave Special Today