If you're hoping to get lost in the rain on your romantic getaway, take a look at these details about year-round temperatures in Yonezawa: The hottest months are usually August and July, with an average temperature of 21°C, while the coldest months are January and February, with an average of 0°C. The rainiest months in Yonezawa are July, December, August and June, with each month seeing an average of 237 mm of rainfall.