Planning for the weather is a good way to make your trip to Hanoi relaxing and enjoyable, especially when you’re splurging. The hottest months are usually June and July, with an average temperature of 29°C, while the coldest months are January and December, with an average of 19°C. The rainiest months in Hanoi are August, July, September and May, with each month seeing an average of 285 mm of rainfall.