If you’re hoping to get lost in the rain on your romantic getaway, check out these details about year-round temperatures in Hagami Onsen: The hottest months are usually August and July with an average temp of 76°F, while the coldest months are January and February with an average of 45°F. The rainiest months in Hagami Onsen are June, July, September, and August, with each month seeing an average of 9 inches of rainfall.