Planning for the weather is an important factor for making your trip to Cát Bà a success, especially when you're splurging. The hottest months are usually July and June with an average temp of 83°F, while the coldest months are January and December with an average of 66°F. The rainiest months in Cát Bà are August, July, September, and June, with each month seeing an average of 15 inches of rainfall.