Spring (February to April) and Autumn (August to October) is the best time to visit Vietnam since these months bring in the lowest rainfall across the country. The conditions are ideal for trekking in the mountains, swimming at the beach and cycling in the countryside. However, Vietnam is a year-round destination, and its weather can be split into tropical and temperate zones. While South Vietnam doesn't see any drastic changes in the weather, North Vietnam experiences distinct seasonal variations.
The best time to visit North Vietnam would be either from March to May or from September to November to experience the clear blue skies and pleasant temperatures. The central provinces of Vietnam are great to visit in the first half of the year (up till April), when they flaunt sunny, beach weather. December to late April or early May is the best time to explore South Vietnam. This coincides with the dry season, and one won’t have to worry about the rainfall and its related complications.