Planning for the weather is a good way to make your trip to Yashima relaxing and enjoyable, especially when you're splurging. The hottest months are usually August and July, with an average temperature of 20°C, while the coldest months are February and January, with an average of -1°C. The rainiest months in Yashima are July, August, December and September, with each month seeing an average of 205 mm of rainfall.