Vietnam boasts the most complex climate of the three Indochina countries and whatever time of year you travel you should be prepared to encounter rain at some point during your trip. Broadly speaking the country can be divided into three main areas - the north, centre and south. The wet season in the north tends to run from May to October and the winter months (November to January) can be quite cool, especially in the Tonkinese Alps but it is mostly dry. Central Vietnam, unusually for Asia, experiences fantastic weather through the summer months enjoying a prolonged dry season from February to early September. The rains arrive here from September to December with January experiencing changeable conditions. Southern Vietnam is typically Asian in climate with the wet season lasting from May to October and the months of November to March proving hot and dry. With the exception of September the diverse climate means there really is no time not to visit Vietnam! That said conditions are generally best from February to April and in November, with the optimum month for travel throughout the entire country being March.
