Halong Bay, located in the northern part of Vietnam, experiences a typical northern Vietnam climate with distinct seasons. The weather in Halong Bay can be divided into different periods:

1. Spring (March to May):
   • Spring is a lovely time to visit Halong Bay when the weather is mild and temperatures gradually rise. Expect daytime temperatures ranging from 20°C to 30°C (68°F to 86°F). This season is characterized by clear skies and a refreshing atmosphere.
2. Summer (June to August):
   • Summer is the hottest and most humid season in Halong Bay. Daytime temperatures can range from 25°C to 35°C (77°F to 95°F). June to August is also the rainy season, with occasional heavy downpours and the possibility of storms. Despite the rain, this period sees lush greenery and the bay is less crowded.
3. Autumn (September to November):
   • Autumn is considered one of the best times to visit Halong Bay. The weather is cooler, and the skies are clear. Daytime temperatures range from 20°C to 30°C (68°F to 86°F). September may still experience some rainfall, but the weather generally improves towards November.
4. Winter (December to February):
   • Winter is the coolest and driest season in Halong Bay. Daytime temperatures can range from 10°C to 20°C (50°F to 68°F). While it’s the coldest time of the year, the weather is still relatively mild compared to northern climates. Winter also sees a higher chance of mist and fog, creating a mystical atmosphere.

Keep in mind that weather conditions in Halong Bay can vary, and unexpected changes may occur, especially during the transition periods between seasons. It’s advisable to check the weather forecast before planning your trip and to bring appropriate clothing for the season, such as light clothing during the warmer months and warmer layers for the cooler seasons.