Despite being a year-round destination, the best time to visit Viet Nam is spring and autumn when the temperature is moderate and rainfall is low. Here is a list of Viet Nam weather splitted by regions:
The far north mountainous area
The climate there is divided into two seasons. The dry season runs from October to March, which provides warm weather and clear days, but bear in mind that the temperature can get freezing cold in December and January. The wet season is from April to September with July and August are the wettest months. The ideal time to visit any provinces in the region is March to April to avoid the bitter cold and heavy rainfall. The last time I was in Sapa, I did not do my homework and travel in July. There was at least 1 hour of rain every day and the trekking trails became very slippery and muddy. Sapa is beautiful in winter with white snow covers everything but there is one problem with it. Snow is rare in a tropical country like Viet Nam so there is definitely a crowd of wide-eyed local people flock to Sapa to see it.
A woman in the far north mountainous area (Source: Internet)
Ha Noi and other provinces in the north enjoy distinct winter and summer season. Ha Noi summer lasts from May to September with the highest temperature reaching 38 degree Celsius. 38 degree is not a big number but remember that you are in a tropical country so this level of heat is harder to bear than in other regions. On top of that, Ha Noi is on its way to become a concrete jungle with more high-rise buildings and fewer trees so the real temperature you feel in the city can reach over 40 degree Celsius. Beware of heatstroke when in Ha Noi for the summer as plenty of local dwellers have suffered from it. Heavy rainfall is another serious problem in rainy season. As the drainage system is poor in the city, it is usually struck by flood and the next thing you know, you are swimming on the streets.
Hanoi in summer (Source: Internet)
Central Viet Nam
From January to August, the temperature can reach a peak at 30 degree Celsius in Hoi An, Hue, and Da Nang. In winter months, rainfall rises to its highest level and the region is threatened by typhoon. The climate in Hue and Hoi An can differ greatly since they are on two sides of a range of mountain. Due to the proximity to the south, the dry season in Quy Nhon is a little bit longer than the other province. Da Lat experiences rainfall from June to October so it is ideal to visit during November to May when the town is drier.
A beach in Central Vietnam (Source: Internet)
South Viet Nam
The temperature in the south usually remains constant year-round between 25 and 35 degree Celsius and the level of rainfall is the only difference between its dry and rainy season. From November to early May, it is slightly hotter and humid. The wet season runs from May to August with short lasting but heavy downpour in the afternoon. There are chances of flood in Sai Gon too in July and August when the rain is highest.
Sai Gon in rainy season (Source: Internet)
Con Dao and Phu Quoc are year-round destinations with several sunny days a year but heavy rain should be expected in wet season.
Best time to visit Viet Nam for those who are on a tight budget
If you are on a tight budget and looking for affordable flights and hotels, March, April, September, and October are the ideal time. In another word, avoiding the tourist season may bring you the best deals. Cheap flights to Viet Nam are available in other months too but accommodation and food can be exceedingly expensive on national holidays. Lunar New Year which lasts from late January to mid-February is to avoid due to extremely high demand on both local and international flights; the price of food and rooms usually rocket unless you are willing to pay to experience Viet Nam New Year.
With the complicated weather system varied by regions, it is hard to determine which the best time to visit Viet Nam is. However, the general rule from vietnamtravelreviews is to avoid the months of high rainfall and temperature.