Not only in Mysore, has almost the entire country received extreme heat from the sun during this time of the year. The summers are unbearable but on the better side, the hotels and transport remain cheap. Since summer is considered an off-season for travel. While the day is not suitable for outdoor exploration, the night remains pleasant and perfect for sightseeing. It is a perfect time to see the stunning Mysore Palace that illuminates at night.
The best season to visit Mysore got to be winters. It is cool and fresh giving a chance to explore the city inside out. This time of the year attracts many travelers not just in Mysore but to travel throughout the country. You can expect temperatures dip down to 15 degrees Celsius which is an ideal time to sightsee and stay outdoors all day without having any difficulty.
Monsoon is soothing and romantic but only if you are indoors, it may not be suitable to explore outside during the rainy season. However, it can be considered a good time to visit Mysore since the temperature is relatively low, not very hot nor cold. You can carry an umbrella, raincoat and start exploring the city. This season is also considered an off-peak time for traveling, so you may get cheaper stays and transport.