If you’re looking forward to lots of outings with your partner, take a look at these details about year-round temperatures in Siddharthanagar: The hottest months are usually May and April, with an average temperature of 31°C, while the coldest months are January and December, with an average of 19°C. The rainiest months in Siddharthanagar are July, August, June and September, with each month seeing an average of 372 mm of rainfall.