Vietnam's elongated shape includes tropical and subtropical zone and is responsible for the varied climate in the country. Generally speaking the best time to travel in Vietnam is when there is a reduced chance of rain; that is during April/May and October/November.
The South (from Ho Chi Minh City to Phan Thiet)
The south is hot year round and has two seasons: one wet the other dry. The wet season lasts from May to October and you can expect daily downpours. These are usually brief and easy to predict. The dry season from November to April is generally sunny and humid.
The Center (from Nha Trang to Hue)
For most of the year Nha Trang is bathed in beautiful sunshine but between November and December the area has heavy rain. Dalat, at an altitude of 1,500m is cooler than the coastal area, particularly from November through to March. Danang and Hue both experience typhoon activity from mid October to mid December when the climate becomes cooler, more overcast and wet.
The North (from Hanoi to Sapa)
Summer in the north lasts from May to October where temperatures range between 30-35 degrees Celsius with the occasional burst of heavy rain. The temperature varies from 10-15 degrees in winter (December to March). February and March can be damp with drizzle and overcast skies.