Planning for the weather is a good way to make your trip to Yilan relaxing and enjoyable, especially when you're splurging. The hottest months are usually July and August with an average temp of 82°F, while the coldest months are January and February with an average of 63°F. The rainiest months in Yilan are October, November, September, and December, with each month seeing an average of 11 inches of rainfall.