September in Hạ Long averages a daily high of 31.1°C. Expect roughly 13.1 wet days totalling 240.3mm. Generally workable, with some weather to plan around.
Across the year, the best time to visit Hạ Long is November–January.
Based on PHU LIEN, VM (48.7km), 1995–2024. 20 years of September data.