The period between October and April is generally considered the best time to visit Hanoi, this being the capital of the country of Vietnam. Compared to the hot and humid summer months of May to September, during which temperatures reach uncomfortable highs, temperatures range generally between 18°C and 25°C, in the range of 64°F to 77°F, from dry December through to February, making it ideal for all activities involving excursions or outdoor activities. Also, you should be warned that December and January are quite cold and sometimes raining, but February begins warming up. Customize your tour according to your preferences, for Hanoi has a distinct charm in every season.
It generally depends on personal weather preference and crowd size: best time to visit Hanoi is the spring months, that is, March-April, and fall months, meaning October-November. These are the times for pleasant weather, with moderate temperatures and low humidity, making it very convenient to sightsee and engage in outdoor activities.
Spring (March-April): Chennai, a little warmer than most other months, is engulfed in celebration in Hanoi, as the Lunar New Year (Tet) will occur in late January or early February.
Autumn (October-November): The prime months for travel, wherein the weather is comfortable with fair skies making swingin around the city and the countryside very pleasant.
Hanoi can get pretty hot and steamy during the height of May-September but it can swing from somewhat chilly and foggy in the winter months from December through February-the window of best visit being around October-November, before the rest of the hordes arrive.