If you're looking forward to lots of outings with your partner, check out these details about year-round temperatures in Itanagar: The hottest months are usually August and September with an average temp of 79°F, while the coldest months are January and December with an average of 63°F. The rainiest months in Itanagar are July, June, August, and September, with each month seeing an average of 24 inches of rainfall.