Phong Nha rainy season: October rain, floods and the caves
The caves keep their hours on paper. A flood upriver decides whether you see them.
VerdictSkip October; from September to November, put the show caves first and keep your dates loose, because a flood shuts the park for days.
The Phong Nha rainy season runs from September to November. At the Đồng Hới weather station on the coast, those three months bring two thirds of the year's rain, and October is the wettest, at about 650 mm over 19 rainy days. The park's board lists daily hours for Phong Nha Cave and Dark Cave in summer and winter alike, but a flood can close the park for days at a time, and Son Doong doesn't run at all from September to the end of December. If rain is your main worry, come between February and August. If autumn is when you can travel, book the show caves and keep your dates loose.
Late October 2025 shows how fast plans change in this season. On 27 October a traveler in Hue, where they said the flooding was "crazy", asked r/VietNam whether to move on to Phong Nha a day early. Another reader was on the way there the next day, after their trekking group had confirmed rain but only minor waterlogging that should clear in a day or so. On 1 November a third traveler asked about reports of parts of Phong Nha up to a metre underwater; they planned to go in a day or two. The next day a reader replied that Jungle Boss Tours had cancelled their cave tour, and the traveler who'd asked had booked flights ten minutes before reading it. Later that day the same reader posted the company's email: "At the moment, all of activity in Phong Nha is closed." The tail of the season can be kind, though: one visitor in the last week of November 2019 had sunny, warm days, with rain on one evening for several hours.
The rainy season month by month
| Month | Mean C | Rain mm | Rain days | Sun hours |
|---|---|---|---|---|
| Aug | 29 | 166.1 | 11 | 198.1 |
| Sep | 27.1 | 472.5 | 15.8 | 168.1 |
| Oct | 25.1 | 649.1 | 19.3 | 129.2 |
| Nov | 22.6 | 318.7 | 17.4 | 95.6 |
| Dec | 19.8 | 125.1 | 14.2 | 73.3 |
August is the run-up and December the tail. November's total falls to about half of October's, but it keeps almost as many rain days, so expect more wet days than the total suggests. For all twelve months, our Phong Nha page has Phong Nha weather by month from the same station, with temperature, rain and fog.
Rain, heat and humidity in the wet months
The wet months are cooler than summer but not cold. Average highs are 30.9°C in September, 28.2°C in October and 25.5°C in November, with average lows of 24.3°C, 22.5°C and 20.3°C. Mean relative humidity is 86% in October, against 70.6% in July, the driest air of the year.
Single days matter more than the monthly total. The largest one-day rainfall in the record, 747 mm, fell in October, more than that month's whole average. September's one-day record is 358.7 mm. Thunderstorms are most frequent in May, at 6.6 days, and September, at 6.2, then almost stop in November, at 0.2.
When floods close the park
Closures follow the rain, not the calendar. On 30 October 2025 the park's tourism center stopped taking visitors at Phong Nha Cave, Tien Son Cave, the Chay River and Dark Cave, and Nuoc Mooc Spring, because of prolonged heavy rain, until further notice; it posts these notices on its Facebook page.
Floods don't keep to the wet months either. After storm No. 5 in August 2025, Phong Nha Cave, Tien Son Cave and Paradise Cave reopened on 27 August after days shut, Nhân Dân reported, with boats taking visitors up a Son River still heavy with red silt. Stream and waterfall sites such as Ozo Park and Mooc Spring took longer: the floodwater had left a thick layer of mud on paths and rest areas, and Ozo Park aimed to reopen from 29 August.
Son Doong runs on its own season. Oxalis Adventure, which runs the expedition, does not operate Son Doong tours from September until the end of December: Son Doong is a river cave, and autumn storms can flood the forest and the cave itself for several days. Its season is from the end of January to the end of August. Some dry caves in the Tu Lan and Hang Tien areas may still run in autumn.
Cave hours and the river in the wet season
The Phong Nha-Ke Bang management board publishes its own notes for each route. It says the underground river at the mouth of Phong Nha Cave is blue-green in the dry season and red in the rainy season. The cave opens daily, from 7:15 to 16:30 in summer and from 7:30 to 15:45 in winter, and a visit takes about 2.5 hours.
The Song Chay and Dark Cave route opens daily from 7:45 to 16:30 in summer and from 8:00 to 15:30 in winter, and takes about 4 hours. The board says the cave's natural mud bath forms from fine mud that collects in the rainy season. Its pages do not say which months count as summer and winter.
Reading the coastal record
The Đồng Hới station is in the city on the coast, listed at 7 m in the regulation's station table. A coastal station can only say so much about the caves inland. Đồng Hới is also a stop on the Hanoi to Hue train.
Vietnam typhoon season counts the storms that came near Phong Nha by month. The central Vietnam in October article compares this record with Hue and Da Nang, while Vietnam's when-to-go guide puts the region beside the rest of the country.
VTV24's report (in Vietnamese) follows Tan Hoa, a village known for deep floods that turned to tourism.
Asked whether to pick Ha Long Bay, Ninh Binh or Phong Nha for a trip in early September, one r/VietNam user replied:
"Phong Nha is very unique. You could do Danag-Hue-Dong Hoi as well. Early September is not quite rainy/monsoon season as well so you should be ok"
u/worldwidetrav on r/VietNam
Our take
October is the month to skip. September and November are wet too, so if those are your dates, put Phong Nha Cave and Paradise Cave first, leave a spare day or two either side, and treat jungle treks as a bonus: Son Doong doesn't run, and operators cancel tours when the water rises. For sun and time outside the caves, May to July is the window we'd pick: it has the most sun and under 116 mm of rain a month. December to March is drier by total but grey, with low sun hours and the year's drizzle and fog.
How we checked this
The climate figures come from 12 tables of QCVN 02:2022/BXD for the Đồng Hới station. The cave hours and the river note come from the Phong Nha-Ke Bang management board's route pages, the 2025 closures from the park tourism center's notice and Nhân Dân, and Son Doong's season from Oxalis Adventure. The late-October scene is pieced together from r/VietNam and r/solotravel posts, read through the Arctic Shift archive. We matched each value against these sources on 21 October 2026.
What this does not tell you
The Đồng Hới station is on the coast and is listed at 7 m. The table does not measure conditions inside a cave, flooding, road closures, or a particular route. It describes the coastal station, not every point in the park. The regulation does not state the observation period of these tables, and nobody publishes a calendar of closures in advance: they follow each flood.
References
- QCVN 02:2022/BXD, National technical regulation on natural physical and climatic data for construction: https://datafiles.chinhphu.vn/cpp/files/vbpq/2022/10/02-bxd.pdf. Checked 2026-10-21.
- Phong Nha-Ke Bang management board, Phong Nha Cave: https://phongnhakebang.vn/du-lich/phong-nha-ky-quan-de-nhat-dong1. Checked 2026-10-21.
- Phong Nha-Ke Bang management board, Song Chay and Dark Cave: https://phongnhakebang.vn/du-lich/tuyen-du-lich-song-chay-hang-toi5. Checked 2026-10-21.
- Phong Nha-Ke Bang Tourism Center, suspension notice of 30 October 2025 (Facebook): https://www.facebook.com/phongnhatourism. Checked 2026-10-21.
- Nhân Dân, "Quảng Trị: Các điểm du lịch tại Phong Nha-Kẻ Bàng mở cửa đón khách trở lại", 27 August 2025: https://nhandan.vn/quang-tri-cac-diem-du-lich-tai-phong-nha-ke-bang-mo-cua-don-khach-tro-lai-post904079.html. Checked 2026-10-21.
- Oxalis Adventure, weather in Son Doong Cave and the Phong Nha area: https://oxalisadventure.com/weather-and-climate-inside-son-doong-cave/. Checked 2026-10-21.
- Oxalis Adventure, Son Doong expedition: what to expect: https://oxalisadventure.com/expectations-of-the-son-doong-expedition-tour. Checked 2026-10-21.
Photo (cover): Tht481 / Wikimedia Commons, CC BY-SA 4.0
Data checked: October 2026.
About the author
Pen name for the weather and climate beat: rain, temperature, typhoons and when to go. Every comparison is built from official station records.
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Disclaimer
This article is general information, not legal, immigration, medical or financial advice. Prices, visa rules and transport schedules change, and each figure shows the month we last verified it. Confirm anything that affects your trip (entry requirements, fees, health rules) with the official government or provider source before you book or travel. The site has no affiliate links today; our affiliate disclosure explains what we will do if that changes.