If you’re hoping to get lost in the rain on your romantic getaway, check out these details about year-round temperatures in Ushio Onsen: The hottest months are usually August and July with an average temp of 75°F, while the coldest months are January and February with an average of 44°F. The rainiest months in Ushio Onsen are July, September, August, and June, with each month seeing an average of 9 inches of rainfall.