If you're hoping to get lost in the rain on your romantic getaway, check out these details about year-round temperatures in Yonezawa: The hottest months are usually August and July with an average temp of 69°F, while the coldest months are January and February with an average of 31°F. The rainiest months in Yonezawa are July, December, August, and June, with each month seeing an average of 9 inches of rainfall.