Weather is probably a major factor when you plan your trip to Katsuyama, and keep in mind that cheaper options are usually available when the weather isn't as good. The hottest months are usually August and July with an average temp of 71°F, while the coldest months are January and February with an average of 35°F. The rainiest months in Katsuyama are July, December, September, and August, with each month seeing an average of 12 inches of rainfall.