Other facts from our historical weather data: When is the rainy season in Nan? Rainy season in Nan occurs in the months of May, June, July, August and September. Does Nan have a dry season? Yes, the months of January, February and December are very dry. Which is the hottest month in Nan? 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 Nan? The coolest month is January with an average maximum temperature of 31°C (88°F). Which is the wettest month in Nan? August tops the wettest month list with 352mm (13.9 in) of rainfall. Which is the driest month in Nan? February is the driest month with 10mm (0.4 in) of precipitation. 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.