Planning for the weather is a good way to make your trip to Yakushima relaxing and enjoyable, especially when you're splurging. The hottest months are usually August and July with an average temp of 80°F, while the coldest months are January and February with an average of 58°F. The rainiest months in Yakushima are June, September, May, and July, with each month seeing an average of 14 inches of rainfall.