Visiting local bars in Dumai is better when you know what the weather holds. These temperatures and rainfall averages can help you choose the best time for bar hopping. The hottest months are usually May and June with an average temp of 81°F, while the coldest months are January and December with an average of 79°F. The rainiest months in Dumai are November, December, October, and April, with each month seeing an average of 14 inches of rainfall.