Weather will likely play an important role when you plan your trip to Yagishiri Island, 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 64°F, while the coldest months are January and February with an average of 30°F. The snowiest months in Yagishiri Island are January, March, February, and December, with each month seeing an average of 24 inches of snowfall.