If you’re looking forward to lots of outings with your partner, check out these details about year-round temperatures in Siddharthanagar: The hottest months are usually May and April with an average temp of 88°F, while the coldest months are January and December with an average of 67°F. The rainiest months in Siddharthanagar are July, August, June, and September, with each month seeing an average of 15 inches of rainfall.