If you’re hoping to get lost in the rain on your romantic getaway, check out these details about year-round temperatures in Yoshioka Onsen: The hottest months are usually August and July with an average temp of 74°F, while the coldest months are January and February with an average of 42°F. The rainiest months in Yoshioka Onsen are September, July, August, and June, with each month seeing an average of 10 inches of rainfall.