Ha Long Bay weather by month

Ha Long Bay weather at a glance

Summer, from May to September, is hot and wet, with daily highs of 30 to 32°C and 183 to 431 mm of rain a month. The cooler months run from December to March, with the drizzle and mist gathered in February and March, and October and November are bright and clear.

The figures on this page are long-term averages for the Bãi Cháy (Bai Chay) weather station, on the north-western shore of the bay, from Vietnam’s national construction regulation. They describe the shore, so conditions out on open water can differ, and the regulation does not publish the exact years behind them: they run from roughly the 1960s to 2017. Sea temperatures are satellite estimates for 1991 to 2020. The packing list is at the end: see what to pack for each season.

The climate year at Bãi Cháy: air and sea temperature, then rain

• Air temperature, daily low to high (°C)
• Sea surface temperature (°C)
• Rain in the month (mm)

Over the year the station averages 23.3°C, with daily highs averaging 26.5°C and lows 20.9°C, humidity of 82.4% and about 1,600 hours of sun. About 1,900 mm of rain falls on roughly 140 days. Most of it comes in a rush: June to September bring 71% of the year’s rain, and November to March only 8%. July is the hottest and sunniest month, August the wettest, December the driest, January the coolest and March the dullest, with about an hour and a half of sun a day.

The bay’s management board, the Ha Long Bay - Yen Tu World Heritage Management Board (the Board), describes two main seasons, winter from November to March and summer from May to September, with April and October as the turns between them. That is a fair summary. The four blocks used on the best time to visit page split the year a little more finely, from the same station figures.

Month by month

Each month below gives the station’s temperatures, rain, sun and humidity, the sea temperature, the mist and drizzle record and the storm risk, with a few lines on what the month means on a boat. The photograph for each month was taken in that month. It shows one day, so it is no forecast.

January

February

March

April

May

June

July

August

September

October

November

December

Sea temperature and swimming

The sea is coolest in February, at 19.2°C, and warmest in August, at 29.8°C. Swimming is allowed only at licensed beaches, and in 2023 Đảo Ti Tốp (Ti Top Island) had the only one operating in Ha Long Bay.

From June to September the water stays between 29.1 and 29.8°C, and May and October are warm too, at 26.9 and 27.8°C. December to April sits between 19.2 and 22.9°C. These are satellite estimates for open water 20 to 40 km outside the main tourist routes; the shallow, river-fed water inside the bay, 5 to 10 m deep on average, can run a degree or two colder in winter and warmer in high summer.

Mist, drizzle and visibility

Mist and drizzle belong to February and March. The Bai Chay station records drizzle on 6.9 days in February and 9.8 in March and fog on 2.5 and 4.2 days, the sky is mostly grey, and humidity peaks at 87.1% in March.

Drizzle, mưa phùn in Vietnamese, falls on about 24 days a year at the station, and February and March hold 69% of them. January has three drizzly days and April just under four; from May to October there are none. Fog or mist is recorded on 10.9 days a year, most of them between January and April. Out on the water fog is probably more frequent than at a shore station, though no one measures it there.

In February and March the station logs 43 to 48 hours of sun a month and 10 to 14 rain days. No visibility record is published for the bay, so “poor views” in these months is a reading of the fog, drizzle and sun figures, without a measured distance behind it. No published rule stops boats for fog either: sailing notices cite storm forecasts and provincial orders. Ask the operator about fog and strong-wind days.

Typhoons and storm warnings

The storm season runs from June to November and is most active from July to September. When a storm approaches, sailings are suspended from a stated hour until the storm’s final bulletin, and the Board posts the notice.

Vietnam’s construction regulation puts the storm season at June to November nationwide. In Vietnamese practice a storm, bão, is a tropical cyclone with winds of force 8 or more; tropical depressions are weaker. Between 1961 and 2025, 114 storms of at least tropical-storm strength passed within 200 km of the bay, about 1.75 a year, and 31 of them reached typhoon strength within that distance, roughly one every two years. Eleven of those 65 years had none at all.

How a suspension works

The port authority, or in some notices the provincial Department of Agriculture and Environment, stops clearing sightseeing and overnight boats to leave port from a stated hour. Overnight cruises are stopped first. Boats already out must bring guests back to the mainland by a stated time, and boats on their way back are still cleared in. The stop lasts until the final bulletin on the storm. The Board posts each notice on its website and the provincial press repeats it, so a guest can check whether a cancellation is official.

Recent notices show the pattern. On 13 June 2025 overnight boats stopped and day boats had to land their guests before 18:00. On 20 July 2025 every tourist boat on the bay stopped being cleared to leave. On 3 July 2026 overnight and evening trips stopped from noon, a day before the storm arrived.

Typhoon Yagi was the hardest test. It made landfall on 7 September 2024, tours stopped from 7 to 12 September, three of the five routes then running reopened on 13 September and all five by 20 September. Twenty-three tourist boats sank at Tuần Châu (Tuan Chau) International Port, and 95% of the greenery at the visitor sites was broken or uprooted.

Squalls that no storm notice covers

Sudden thunderstorm squalls are the gap. On 19 July 2025 a day boat capsized in a squall near Hang Đầu Gỗ (Dau Go Cave): 49 people were aboard, 39 died and 10 were rescued. Accounts of the warnings differ. Quảng Ninh officials said the bay forecasts at 06:30 and 10:00 gave winds of force 2 to 3 and the squall warning came at 13:30, after the boat had left a little before 13:00; the national forecasting centre said a 04:30 marine bulletin had mentioned possible tornadoes, with alerts at 11:45 and 13:30.

By July 2026 an online warning system for thunderstorms, squalls and lightning covered Ha Long and Bai Tu Long bays, giving about 30 minutes’ notice across nine zones to boat owners and tourism businesses. Its own report stresses that storms at sea come fast and cover small areas. Since August 2025 six sheltered spots along the sightseeing routes have been set aside for boats caught by a squall, and military medical vessels and patrol boats watch the bay around the clock.

What to pack for each season

Layers suit December to March, light clothes with a jumper suit April, May, October and November, and quick-drying clothes with swimwear suit June to September.

Questions visitors ask