Ha Long Bay in May: sunniest month, turning wet

May on Ha Long Bay is hot and bright, and the rain is building. Ten years of modelled weather give days of 29.1°C and nights of 25.5°C, with more sunshine than any other month, 9.4 hours a day, and a sea of 29.3°C. The limitation is the rain. May averages 177 mm, more than two and a half times April’s 68 mm, and about 5.5 days a month bring 10 mm or more.

Review figures come from the 851 reviews posted in May, of 10,058 dated reviews for 74 boats counted on 16 October 2026. A review’s date is the day it went up, which can be days or weeks after the trip.

What is the weather like in May?

Hot and sunny between downpours. These are May averages for 2016 to 2025 from ERA5 reanalysis, a model grid about 25 km wide that smooths out the extremes.

May, 2016–2025	Average
Daytime high	29.1°C
Night-time low	25.5°C
Coolest night in the ten years	19.1°C (3 May 2022)
Warmest day in the ten years	34.2°C (27 May 2024)
Days with 1 mm of rain or more	17.5
Days with 10 mm of rain or more	5.5
Rain in the month	177 mm (57 mm in the driest year, 278 mm in the wettest)
Wettest day in the ten years	101.9 mm (13 May 2016)
Sunshine	9.4 hours a day
Sea-surface temperature	29.3°C (three Mays)

The nights are what change most from April. In an average May the low stays at 25°C or above on about 20 nights, against three in April, so check that your cabin’s air conditioning can be left on overnight. Days reach 30°C on about ten. The rain total swings widely from year to year, from 57 mm in 2020 to 278 mm in 2019, and four May days in the decade topped 50 mm.

The last eleven days are the cloudiest. From 21 to 31 May cloud averaged 78% and an average year had 7.4 days with a millimetre of rain or more; the first and second ten days had about five each, with cloud at 67% and 65%. Sunshine held above nine hours a day in all three.

A Lyra Grandeur guest posting on 27 May 2026 went on a bike ride across an island in heavy rain with the guide and made the best of it; the same guest was upset by rubbish floating in the bay, which they put down to the local authorities. A Verdure Lotus Classic guest posting the same day waited about an hour outside a small, crowded terminal in the heat before a shuttle boat with no air conditioning; things improved once on board.

Can you swim in May, and is the sea rough?

The sea is warm. It averaged 29.3°C over three Mays, from 26.7°C on the coolest day to 31.5°C on the warmest. Several La Pandora guests posting on 23 May 2026 swam in the bay, and an Ambassador Signature guest posting on 7 May 2026 used the slide.

Waves on Ha Long Bay stay small in May: across four Mays the highest wave of an average day was 0.39 m on open water, and the biggest of the 124 days reached 0.86 m. Gusts of 50 km/h or more came on 40 May days in ten years, 4.0 a year, against 3.3 in April. None of the decade’s 50 gustiest days fell in May, but June has almost twice as many gusty days, 72. Our weather guide explains who decides whether boats sail.

Kayaking comes up in 94 of the 630 May reviews we have classified, 14.9%, against 699 of 6,330, 11.0%, in the other months, a gap larger than chance would explain. Whether it is on your boat’s programme is worth checking when you book.

Is May busy, and do the holiday surcharges still apply?

May’s first three days fall inside the 2027 national holiday, the crowded week. Across the whole month May sits mid-table, sixth of twelve months by reviews posted. The holiday for Reunification Day and Labour Day runs from Friday 30 April to Monday 3 May 2027, as reported by Tuổi Trẻ on 11 October 2026, so Saturday 1 May to Monday 3 May falls in it. Our April guide has the visitor figures for that week.

Some boats charge for 1 May. Cozy Bay Grand lists 200,000 dong, about $8, a person for 1 May in its 2026 price guide, read on 16 October 2026. Aqua of the Seas charges $25 a person for 30 April only, so a boarding on 1 May falls outside its line as written. For any other boat, ask your seller for the 2027 figure and whether 2 and 3 May count.

May has 851 reviews posted against 1,123 in April, a count that tracks guest numbers only loosely. Crowd words turn up in 21 of the 771 May text reviews, 2.7%, against 2.9% across the year, a gap small enough to be chance.

One guest’s cruise was cancelled for weather. Posting on 2 May 2026, they say they accepted that the weather made cancelling necessary, but nobody told them: they found out when they rang the driver, who was late for their hotel pick-up, a day after being asked for their passport details.

Are May reviews better or worse than average?

May’s share of one and two star reviews is a little above the average, by a margin small enough to be chance. As posted, 49 of the 851 May reviews (5.8%) sit at one or two stars, against 520 of 10,058 (5.2%) across all months, and only December and March are higher. May 2026 supplies 22 of the 49, in line with its 387 of the 851 reviews, and the thin Mays of 2023 and 2024 ran higher.

May posted in	Reviews	One or two stars	That whole year
2023	56	4 (7.1%)	8.8%
2024	103	7 (6.8%)	5.8%
2025	277	13 (4.7%)	5.5%
2026	387	22 (5.7%)	3.4% (to 10 October)

Seven thinner Mays, 2016 to 2022, add 28 reviews and three low scores.

May 2026 ran at 22 low scores in 387 reviews, 5.7%, against 105 in 3,331 for the rest of 2026 to 10 October, 3.2%, a difference unlikely to be chance. The 22 are spread over 16 boats, and no boat has more than four. May 2025, on 277 reviews, came out better than its own year.

Of the 33 low May reviews we have classified, 14 mention value for money (42.4%, against 111 of 353, or 31.4%, for low reviews in all months) and 21 the food (63.6% against 56.4%). Thirty-three is a small sample, and neither difference is large enough to rely on.

Which boats did well in May?

La Pandora, Ambassador Signature and Orchid Classic had the most May reviews, and almost none of them low. Among boats with 100 or more reviews collected over at least a year, they are the only three with 50 or more May reviews, and between them they have two at one or two stars, counted on 16 October 2026.

Boat	May reviews	One or two stars in May	All reviews	Five stars, all reviews
La Pandora	94	0	395	95.4%
Ambassador Signature	65	1	379	95.8%
Orchid Classic	51	1	354	90.4%

La Pandora has the most May reviews of any boat we list and none of them low. The Ambassador Signature guest who used the slide also cycled to Viet Hai village and found an anniversary cake left in the room. Two Orchid Classic reviews posted on 21 May 2025 thank the chef for gluten-free meals, one of them for the whole trip, and one adds that they were dairy-free too. Another, posting on 16 May 2026, liked the scenery best at dusk and in the early morning mist, and thought the trip fairly expensive but worth it for the memories.

What should you ask before booking a May cruise?

Four questions, by email, so the answers are in writing.

1. Is 1, 2 or 3 May in your holiday window for 2027, and what is the surcharge in dollars for each adult and each child?
2. If weather stops the boat sailing, how and when will you tell me, and what happens to my money?
3. How long is the wait at the harbour, and is it under cover?
4. Is swimming from the boat on the programme, and is there a slide or a ladder?

Families should also read our guide to cruising with children, and the cancellation policy guide shows how much the ordinary terms differ.

May cruise questions

Is May a good month for a Ha Long Bay cruise? In our view, yes if you like heat and can live with showers. May has the most sun of any month, 9.4 hours a day, and a sea of 29.3°C, but it averages 177 mm of rain and nights stay near 25°C. Of the 851 May reviews counted on 16 October 2026, 5.8% give one or two stars, a little above the 5.2% average. The month by month comparison ranks it against the rest.

Does it rain every day in May? No, but it rains often. An average May on Ha Long Bay has 17.5 days with a millimetre of rain or more and 5.5 with 10 mm or more, and 21 to 31 May has the most rainy days. The total swings from year to year, from 57 mm in 2020 to 278 mm in 2019, so a dry week is possible. Sunshine still averages over nine hours a day in every part of the month.

What should I pack for May? For a May cruise on Ha Long Bay, pack light clothes, sun protection and a rain jacket: the month averages 177 mm of rain. Days average 29.1°C and reached 34.2°C at the hottest, on 27 May 2024; nights average 25.5°C, so you will not need a jumper on deck. Pack swimwear: the sea averages 29.3°C.