Other facts from our historical weather data: When is the rainy season in Vientiane? Rainy season in Vientiane occurs in the months of May, June, July, August and September. Does Vientiane have a dry season? Yes, the months of January, February and December are very dry. Which is the hottest month in Vientiane? April has an average maximum temperature of 37°C (99°F) and is the hottest month of the year. Which is the coolest month in Vientiane? The coolest month is January with an average maximum temperature of 30°C (86°F). Which is the wettest month in Vientiane? August tops the wettest month list with 400mm (15.7 in) of rainfall. Which is the driest month in Vientiane? December is the driest month with 9mm (0.4 in) of precipitation. Which is the sunniest month in Vientiane? December is the sunniest month with an average of 249 hours of sunshine. No idea where to travel to this year? We have a tool that recommends destinations based on your ideal conditions. Find out where to go with our weather planner.