Peninsular India is privy to seasonal transition thunderstorms twice a year. The first one happens around March / April when the Easterlies gradually turn to Westerlies. The second happens during September / October when the westerlies give way to Easterlies. These two transitions are effectively the start of a larger process namely Southwest Monsoon and Northeast Monsoon. The transition around March / April coincides with the flowering season for plants like Mango / Coffee. So locally they are called Coffee Showers / Mango Showers as the case be depending on areas.
These coffee showers / mango showers are an essential part of the flowering season. They provide much needed moisture when the plants are ready to flower. At times intense thunderstorms also play havoc especially if it is accompanied by hailstorms. Typically these mango showers / coffee showers start showing up along the Western Ghats. A combination of westerlies first showing up along the West Coast and the orographic lift aid these thunderstorms.
Over the next couple of days an interaction of lower level Easterlies and Westerlies is likely to trigger thunderstorms. The traditional coffee growing areas over Karnataka like Chikmagalur, Kodagu are in line for rains. We have seen in the past interactions like this tend to enhance thunderstorm potential. In addition to Karnataka, most parts of Kerala may see widespread thunderstorms. Places adjoining the Ghats in Tamil Nadu are also likely to see thunderstorm activity. Places like Nilgiris, Valparai in the Ghats may see fairly heavy spell of rains. Additionally some places in West interior TN and South TN may also see moderate to heavy rains during the weekend. As of now places like Chennai in North Coastal TN may at best see some light rains.
After this spell of enhanced Mango Showers the one to watch out for is the 1st active phase of Summer over Tamil Nadu. Weather models have been consistently indicating increasing temperatures from Monday / Tuesday across the state. There is a very high possibility during the upcoming week one or two stations in the state may see its 1st 40°C of the year. The upcoming week may also notch up heat over North Coastal places like Chennai.