What to wear to Halong Bay in Vietnam in June+10, 5438? Is the temperature difference big?

The latitude of Halong Bay is between Guangxi and Hainan. January is his coldest season. Extreme temperature is not excluded when the temperature is between 25- 15.

Generally, you can wear thin sweaters, thin warm clothes and sportswear. The sun is certainly not too strong, but sometimes the sea breeze is also very strong.