Vietnam experiences a fair degree of diversity in climate. The north has distinct summer and winter seasons some lasts from May until October, when the weather is hot and very humid with temperatures averaging about 30 degrees Celsius. November to April are the winter months when the temperature is mainly dry and average temperatures are about 18-20 degrees Celsius. Please note that in the mountainous regions of the country, temperatures will be much lower than this, so warm clothing is required if you are traveling to hill tribe areas during the winter months.
The North ( From Northern mountains to Danang)
Areas north of the 18th Parallel have two seasons: winter and summer. Winter last from around November to April, quite cool and wet, February and March are marked by a persistent drizzling rain. The hot summer runs from May to October, very high humidity and it is also the season of occasional typhoons.
The Central ( From Danang to Nha trang)
Nha Trang and north central coastal lowlands have a long dry season from late January to October, accompanied by fog and fine drizzle. Other coastal lowlands are denied significant rainfall from the southwestern monsoon (April or May to October) by the Truong Son Mountain Range. It is very wet period. Dalat like the rest of central hightlands is much cooler than the Mekong Delta and the coastal strip. Its dry season is from December to March.
The South ( From Nha Trang to Mekong Delta )
The South has two main seasons: the wet and the dry. The wet season last from May to November (June to August are wettest months). There are heavy but short lived downpours almost daily, in the afternoon.
The dry season runs from December to April (Late February to May are hottest and very humid). It is also the begining of rainy season. In Ho Chi Minh City, average annual temperature is 27°C, average humidity is 80% and annual rainfall averages 1979 mm.