Northern Vietnam (Hanoi, Halong Bay and Sapa) can be quite cold, damp and misty from November to March, but it’s also possible to experience lovely sunny, cloudless days during this period. You might need warm clothing and a waterproof jacket in case of rain, but these can be cheaply purchased locally if required.
The central region (Hué, Hoi An, Danang and Nha Trang) is at its wettest from September through to December. Traditionally, this period sees monsoon rains and occasional typhoons that can cause flooding in the area. While this is rarely of such a level as to seriously affect an itinerary, we do advise people traveling in this area over this period that there may be last-minute changes to itineraries to accommodate the weather conditions.
Some people might say that the summer months (June, July, August) are the best time to visit Vietnam. Unusually for Asia, the weather in central Vietnam is likely to be sunny and clear during this time, and although there may be short downpours in the south and north, many people see no rain at all and enjoy cloudless sunny skies.
Southern Vietnam will be very humid, and thunderstorms can’t be ruled out, but these generally clear the air and don’t prevent you from sightseeing.