Halong Bay is situated in the Northeastern part of the country, its weather is different in 4 seasons but it can be mainly divided into cold dry winter and hot humid summer.
Winter in Halong Bay lasts from November to March which lead to cold weather, getting colder in Jan, Feb… not ideal for swimming. The foggy days or strong monsoon are also visible this time. Despite of this season feature, this time rises as high season of Halong Bay tourism. The temperature is from 12ºC to 20ºC
Summer time lasts from May to early September, as other part of the Northern country, the Bay is sunny and hot for swimming under clear blue sky. There is light rain in some days and even unexpected typhoon that might cancel your trip. Temperature rises from 25ºC. Summer promotion rate can be found during this time.
Spring ( March, April) and Fall ( September, October) seems to be the best time to visit Halong bay, the weather is cool and you enjoy the best time of the year.
It is fine to visit Halong Bay all year around. Even though there are some unexpected cases leading to trip cancellation. Each season will bring you a different feeling that you will never forget.