Northeast Vietnam has a cool to cold season (courtesy of the northeast monsoon from November to March) and a warm to hot wet season (from April to October). December and January in particular can get quite frosty in the far north of Vietnam - pack accordingly. This time of the year can also see heavy mists that can run for days - these can reduce visibility in places like Sapa and Ha Long Bay to frustratingly short distances. The wettest months of the year in Hanoi are July and August, the driest, December and January.