Planning for the weather is an important factor for making your trip to Vientiane a success, especially when you’re splurging. The hottest months are usually April and March, with an average temperature of 29°C, while the coldest months are January and December, with an average of 24°C. The rainiest months in Vientiane are August, July, September and June, with each month seeing an average of 405 mm of rainfall.