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 Kumamoto: The hottest months are usually August and July, with an average temperature of 25°C, while the coldest months are January and February, with an average of 8°C. The rainiest months in Kumamoto are June, July, August and May, with each month seeing an average of 331 mm of rainfall.