The dry, cool season runs from October to April and is the best time to visit. December and January are coolest, around 15-20°C — slightly chilly by tropical standards but pleasant for walking the city.
May to September is hot, humid, and wet. Typhoons sweep across the Gulf of Tonkin between July and September and can cause serious flooding and disruption to boat services. The summer months are also when most domestic tourists head for Cát Bà and Đồ Sơn, so transport is busy and prices for hotels and ferries rise. The major buffalo-fighting festival at Đồ Sơn is in the eighth lunar month (usually September).
The Tết lunar new year holiday, in late January or February, sees the city virtually shut down for a week. Many restaurants, shops, and offices close — book accommodation well in advance and expect a quieter, somewhat surreal city.