Ha Long Bay weather by month: ten years of numbers

Ha Long Bay has a hot, wet half of the year from May to September and a cooler, drier half from November to April, with October in between. August is the wettest month on ten-year averages, at 456 mm and about 25 days with rain, and December is the driest at 19 mm. The strongest-wind days cluster between July and October, and on our count September is the quietest of those four months.

Every weather figure here is our own calculation from daily data for the bay’s coordinates, 2016 to 2025, downloaded from Open-Meteo on 30 September 2026. The data is ERA5 reanalysis from ECMWF, a model’s reconstruction of the weather over a grid square roughly 25 km across. No weather station sits behind it. The grid smooths extremes, so a station caught in a typhoon usually records stronger gusts and heavier rain, and every storm number below is an indicator. Sea temperature covers only November 2022 to 2025, and wave height October 2021 to 2025, both taken at a point in open water. We did not pull separate data for Lan Ha Bay or Bai Tu Long.

What is the weather like in Ha Long Bay by month?

Warm to hot from May to October, mild and often grey from January to March, with most of the year’s rain falling between May and September. These are averages over ten years for one point in the bay.

Month	High °C	Low °C	Rain mm, average (driest–wettest year)	Days with rain	Sunshine h/day	Cloud cover %	Sea °C
Jan	19.5	15.6	45 (4–129)	8.5	5.8	65	18.6
Feb	20.0	16.0	41 (5–97)	7.0	5.3	70	18.6
Mar	23.1	19.0	39 (8–65)	8.9	5.7	71	21.0
Apr	26.5	22.2	68 (46–104)	9.9	8.2	63	25.7
May	29.1	25.5	177 (57–278)	17.5	9.4	70	29.3
Jun	31.1	27.7	235 (101–395)	19.9	9.0	85	31.5
Jul	31.0	27.4	354 (128–687)	22.2	9.1	81	31.8
Aug	30.6	26.7	456 (181–622)	25.3	8.0	85	31.7
Sep	30.1	25.9	365 (182–717)	21.3	8.6	70	30.6
Oct	27.8	23.5	182 (45–487)	13.1	8.4	58	28.3
Nov	24.9	20.7	45 (18–80)	8.0	8.2	52	25.1
Dec	20.9	16.7	19 (3–68)	3.9	6.8	60	21.1

A day with rain means at least 1 mm. Sea temperature is the average of three years of data, four for November and December.

Read the bracketed range before the average. October has been as dry as 45 mm in one year of the ten and as wet as 487 mm in another.

When is the rainy season in Ha Long Bay?

May to September, with October as a toss-up. Each of those five months averages 177 mm or more, against 68 mm or less in every month from November to April.

August is the wettest on average: 456 mm, rain on about 25 days, and 7.1 days a month with 20 mm or more. The wettest single months in the ten years were not Augusts, though. The top one was a September, at 717 mm, followed by a July at 687 mm, while August’s worst came to 622 mm. The heaviest single day in the whole record was 7 September 2024, with 191.8 mm.

December is the driest month, 19 mm on average and rain on about four days.

Few reviews dwell on rain: fewer than 30 of our 8,316 mention it.

When is typhoon season, and which months had the strongest winds?

July to October. We ranked all 3,653 days from 2016 to 2025 by their strongest gust, and 43 of the 50 windiest days fell in those four months: 15 in July, 13 in August, 9 in October and 6 in September.

Counting days flatters months where one storm blew for two days running. Grouped into separate storms, the 20 windiest days make 15, four each in July, August and October, and three in September. September’s share is small, but it holds the strongest day in ten years by a distance.

Date	Strongest gust km/h	Rain mm	Open-water wave height m
7 Sep 2024	185.4	191.8	2.88
10 Oct 2021	109.4	109.2	0.64
22 Jul 2025	103.7	27.0	1.24
25 Aug 2025	94.0	97.4	1.36
4 Jul 2019	93.6	8.3	no wave data

Two guests name the 7 September 2024 storm Typhoon Yagi. A Capella guest posting on 5 September 2024 wrote that the boat had to be evacuated because of it, and an Emperor Cruises guest posting on 22 September wrote that the pearl farm stop had been dropped because Yagi had destroyed it.

October’s windy days in the top 20 fell on the 10th, 11th, 14th and 29th, in 2017, 2020 and 2021, so the tail of the season is not confined to the first week; our October guide has the detail.

June is the odd one. It has the most days with gusts of 50 km/h or more, 7.2 a year, but only three of the 50 windiest, and 32 of its 72 gusty days came in 2020 and 2021.

Wave heights at the open-water point stay small all year. The day’s highest wave averages between 0.33 and 0.44 m in every month, and waves of a metre or more occur on about four days a year, 1.3 of them in a typical September. Among the islands the water is more sheltered, so on board you would likely feel less than these figures.

What happens to my cruise if a storm comes?

Paradise Vietnam’s weather page, read on 6 August 2026, says the port authority usually makes the call at 3 pm on the day you sail. If you are already at the marina and the trip is called off, it keeps $25 a head for the lunch served while you wait and refunds the rest, and a two-night trip that loses its second day is billed as one night. Other sellers write it differently.

One guest booked for 26 September 2025 names Typhoon Ragasa, and the windiest days in our data that week were 28 and 29 September, with gusts of 86.8 and 91.8 km/h. An Indochine Cruise guest posting on 24 September 2025 sailed just before what they called a super typhoon and was back before the bay closed. A Catherine Cruise guest, in a review posted in August 2025, went a couple of days after a typhoon, found the boat very quiet and rated the two-night trip five stars.

Cancellation words peak in reviews posted in August, 9 of 803, and at least five of those describe trips called off for weather in the second half of August 2025. Before paying for July to October, ask by email what a closure on your date means and how much comes back if two nights become one. Our cancellation policy guide shows how widely the ordinary penalty ladders differ.

Does stormy weather mean a worse trip?

Not on the 8,316 reviews we hold. July is as stormy as any month and has the best reviews of the year, while September has fewer big-wind storms than July, August or October and the worst reviews.

Month	Storms among the 20 windiest days	Average rain mm	Reviews posted	One or two stars
Jul	4	354	878	2.8%
Aug	4	456	803	4.6%
Sep	3	365	336	9.8%
Oct	4	182	529	6.2%

The weather does not explain September’s scores. Only 2 of its 33 one- and two-star reviews mention a storm, and the worst September for reviews, 2023, had no storm among our 50 windiest days.

A review is posted days or weeks after the trip, so a month here is only roughly the month people sailed, and our reviews run to 12 August 2026, so September to December have one year fewer. We also cannot tell you how many trips were cancelled outright. No port or seller we have read publishes a count; the one estimate we found, on Lux Cruises’ FAQ page read on 10 August 2026, is about five days a year. For which month to pick, our month-by-month review comparison is the page to read next.

Is Ha Long Bay cold in winter?

Cool by day and chilly at night. January averages a high of 19.5°C and a low of 15.6°C, February 20.0°C and 16.0°C, December 20.9°C and 16.7°C. The coldest night in ten years was 5.1°C on 24 January 2016, and a typical January brings about four nights below 12°C.

Cold weather comes up in 8 of December’s 644 reviews and 7 of January’s 727, the two highest shares of any month once cold food and drinks are set aside. A December guest found the deck too chilly to lounge on between stops, and a March guest’s crew set dinner indoors for the same reason. Pack a warm layer and something windproof.

Our records for the 70 boats do not track cabin or pool heating. A few operators do say it on their own sites. Calista’s services page describes a 225 m² heated infinity pool open year-round, and Lyra’s homepage lists a heated pool and jacuzzi, both read on 10 August 2026; we have not checked either in January. An Aspira guest in February 2024 found the rooftop pool unheated. Among boats with 40 or more reviews posted December to February, Alisa Premier, Orchid Trendy and Orchid have the fewest one- and two-star scores, 1.3 to 1.9%. On any boat, our luxury cruises included, get the heating answer in writing.

Can you swim in Ha Long Bay, and how warm is the sea?

Yes from May to October, when the sea at our open-water point averages 28.3 to 31.8°C. November and April are around 25°C, and from December to March it drops to 18.6 to 21.1°C, with a coldest single day of 17.0°C in February.

An Orchid Trendy guest who sailed at the end of December 2024 loved the kayaking and found the water too cold to swim. Kayaking needs no warm water, and our kayaking guide explains which boats include it. The catch for swimmers is that the warmest water, June to September, comes in the months when storms can take a day.

When is it foggy, and will you see the karsts?

March is the month guests mention fog and mist most. Our weather data has no fog or visibility measure, so this rests on reviews plus cloud and humidity.

February and March average 70 and 71% cloud cover, and March’s humidity of 86% ties with August for the highest of the year. Yet March is one of the driest months, at 39 mm: a grey March is mostly cloud and damp air with little rain.

Fog, mist or haze comes up in only 10 of 8,316 reviews, and half of them, 5 of 795, were posted in March. Most who mention it liked it. An Alisa Premier guest in March 2025 found the fog made the bay feel mysterious and still beautiful; only a Nostalgia guest a year earlier said cloud and fog cut into the views. We cannot tell you how many March mornings are fogged in; nothing in our data records it.

Which month has the clearest skies?

November. It has the least cloud of the year at 52%, 8.2 hours of sunshine a day, 45 mm of rain, and none of the 50 windiest days in ten years. The sea is still around 25°C.

October comes next on cloud, at 58%, but carries the end of the storm season. November to May together held only four of the 50 windiest days.

Questions about Ha Long weather

Will it rain every day in August? Most days, on the averages. August gets at least 1 mm of rain on about 25 of its 31 days, and 20 mm or more on about seven. Our data is in daily totals, so it cannot tell you whether that rain falls as a short afternoon burst or over the whole day.

How cold is Ha Long Bay in January? Cool by day and chilly at night. January averages a high of 19.5°C and a low of 15.6°C, with 5.8 hours of sunshine a day and 45 mm of rain. December and January draw the most mentions of cold weather in our reviews, eight and seven. Pack a warm layer and a windproof jacket for the deck, and ask whether the cabin is heated, because few listings say.

Is March foggy in Ha Long Bay? March draws more fog and mist mentions than any other month, five of its 795 reviews and half of all we hold, and it has the highest humidity of the dry season at 86%, with 71% cloud cover. Most guests who mention the mist liked it; one said cloud and fog cut into the views. We cannot give you a count of foggy days, because the weather data has no visibility measure.

Is December a good month for weather? It is the driest month, 19 mm on average with rain on about four days, and only one of the 50 windiest days in ten years fell in December. The trade is temperature: a 20.9°C average high, a sea around 21°C, and 8 of December’s 644 reviews mention the cold.