Taking into account the local weather in Otsuki is an important factor for planning your visit, especially if you plan to spend your trip poolside. The hottest months are usually August and July with an average temp of 68°F, while the coldest months are January and February with an average of 35°F. The rainiest months in Otsuki are July, September, October, and June, with each month seeing an average of 11 inches of rainfall.