Hanoi's best weather, spring's tail end into autumn's start: comfortable temperatures, less rain than the summer monsoon, and a break from winter's cold, clammy skies. Late October into November is the more reliable of the two windows, April can still catch the very end of a cool spell or the first build-up of pre-monsoon heat. Book ahead if aiming for the second half of either month, they're genuinely the best weeks of the year here.

This tier covers real variety. December is markedly better than the months right after it, sunnier and less cold, though still firmly winter. March sits at the tail of the cold season, damp and still mostly sunless, but warming fast. May, June, and July are deep in the hot, humid build toward the wettest months, uncomfortable at times but not the worst the year has to offer. September holds onto summer's heat and rain a while longer before autumn properly arrives.

January and February are Hanoi at its least inviting: cold, persistently overcast, drizzly, and this is also when air pollution regularly climbs to its worst levels of the year. August, on the opposite end of the calendar, brings the heaviest rain and the muggiest heat of the wet season. None of these months are dangerous to visit, but they're a real step down from the rest of the year.