If you're looking forward to lots of outings with your partner, take a look at these details about year-round temperatures in Itanagar: The hottest months are usually August and September, with an average temperature of 26°C, while the coldest months are January and December, with an average of 17°C. The rainiest months in Itanagar are July, June, August and September, with each month seeing an average of 616 mm of rainfall.