Because of its geography, the climate in Vietnam varies greatly from north to south with three distinct climatic zones. Tropical monsoons occur from October to April in the centre and from May to September in the north and south. It is almost totally dry throughout the rest of the year. It can get exceptionally hot, however, all year round, but the north has a cooler time between October and April. Temperatures around the country can reach up to 40C in the height of the hot and rainy season (May to September), but the northern highlands and Hanoi can often seem chilly and damp in the winter.
There is no one ideal time to visit Vietnam as a whole but at any time of year there will be sun somewhere. The high season is from September to March but bad weather can disrupt travel in the centre of the country during this period, particularly from September to December. For the beaches in the centre of Vietnam, Danang, Hoi An and Nha Trang, it is best to go between May and August. The autumn is the best time to visit Halong Bay when there should be clear skies.