Planning for the weather is an important factor for making your trip to Wakura Onsen a success, especially when you’re splurging. The hottest months are usually August and July with an average temp of 74°F, while the coldest months are February and January with an average of 41°F. The rainiest months in Wakura Onsen are July, September, August, and December, with each month seeing an average of 10 inches of rainfall.