Planning for the weather is an important factor for making your trip to Senami Onsen a success, especially when you're splurging. The hottest months are usually August and July, with an average temperature of 23°C, while the coldest months are February and January, with an average of 3°C. The rainiest months in Senami Onsen are July, December, January and August, with each month seeing an average of 257 mm of rainfall.