Planning for the weather is a good way to make your trip to Guiuan relaxing and enjoyable, especially when you're splurging. The hottest months are usually August and June with an average temp of 83°F, while the coldest months are February and January with an average of 81°F. The rainiest months in Guiuan are January, December, November, and July, with each month seeing an average of 17 inches of rainfall.