If you’re looking forward to lots of outings with your partner, take a look at these details about year-round temperatures in Patna: The hottest months are usually May and April, with an average temperature of 32°C, while the coldest months are January and December, with an average of 20°C. The rainiest months in Patna are July, August, September and June, with each month seeing an average of 280 mm of rainfall.