If you’re hoping to get lost in the rain on your romantic getaway, check out these details about year-round temperatures in Gangtok: The hottest months are usually June and August with an average temp of 65°F, while the coldest months are January and December with an average of 48°F. The rainiest months in Gangtok are July, August, June, and September, with each month seeing an average of 36 inches of rainfall.