Vejret i Con Dao (Con Son) i december

Con Đảo's forum places September inside southern Vietnam's June-through-October monsoon window, but posters were clear it's rarely a washout - the typical pattern is an hour or so of rain that clears back to sun, with some visitors reporting genuinely sunny, hot days and rain arriving mainly late in the evening or overnight. Mainland weather forecasts were repeatedly called unreliable for the island specifically, so posters recommended just watching the sky rather than trusting an app. Flexible plans matter more than picking an exact date within the month.

Forum posters consistently name March among the best months here, with sunny, warm weather and calm, clear seas typical this time of year - part of a broader dry season posters place roughly October through March for southern Vietnam generally, though some extend Con Dao's own good-weather window all the way to December. Posters are clear Con Dao runs its own genuine microclimate distinct from the mainland: forecasts based on general southern Vietnam conditions are often wrong for the island specifically, so posters recommend treating mainland weather apps as unreliable and instead checking conditions once actually on Con Dao or close to departure.