Thunderstorm with heavy rain is likely to occur at isolated places over Nilgiris, Erode, Perambalur, Krishnagiri, Salem and Ariyalur districts of Tamilnadu.
Thunderstorm with Light to moderate rain is also likely to occur at many places over rest districts of Tamilnadu, Puducherry & Karaikal area.

HEAVY RAINFALL WARNING:

Today (20.11.2021): Thunderstorm with heavy rain is likely to occur at isolated places over Nilgiris, Erode,Perambalur, Krishnagiri, Salem and Ariyalur districts of Tamilnadu.
Tomorrow (21.11.2021): Thunderstorm with heavy rain is likely to occur at isolated places over Ariyalur, Perambalur, Kallakurichi, Cuddalore and delta districts of Tamilnadu and Karaikal.

THUNDERSTORM WARNING:

Day 1(20.11.2021) to Day 4 (23.11.2021): Thunderstorm with lightning is likely to occur at isolated places over Tamil Nadu, Puducherry and Karaikal area.
LOCAL FORECAST FOR CHENNAI CITY AND NEIGHBOURHOOD:
For next 24 HRS: The sky condition is likely to generally cloudy. Thunderstorm with Light to moderate rain is
likely to occur in some areas. Maximum and minimum temperature is likely to be around 30 0C and 25 0C

Reference:
http://imdchennai.gov.in/tn_fc.pdf
http://www.imdchennai.gov.in/hrw_district.htm