21st century averages (2000 to 2019)
The festival is during the core winter season over India ..
1. South Indian coastal plains
South East India ( Tamilnadu Andhra) has it's mildest weather of the year during this period. The temps are range bound (don't deviate much from the average).
South West India (Coastal Karnataka , Kerala ) has warmer weather than South East India coast. Kerala coast has almost tropical weather. Night temps decrease a bit as we move away from the coastline though days remain warm.
2. South Indian Deccan plateau
Southern Deccan Plateau (Interior Karnataka , Telangana) has
fine,dry weather during this time of the year.
Southern Deccan plateau is less prone to the cold night temps of the Northern Deccan Plateau (Maharashtra).
Also, it has comparatively less extremes of diurnal temp range than North Deccan plateau.