Phong Nha has three seasons. From February to August it is the main cave season: drier, and hot from May, when the dry Laos wind can push temperatures past 40°C. From September to November come the heavy rains, peaking in October, with floods that close the caves and the river trips. From December to February it is cool, grey and drizzly. The show caves open year-round except in storms, while Son Doong and the other expedition caves run only from about January to August.
Phong Nha is the gateway to Phong Nha-Ke Bang National Park, a UNESCO site of limestone mountains and giant caves. Since the 2025 reforms, the village is part of Phong Nha commune in Quang Tri province, which absorbed Quang Binh, with its provincial capital at Dong Hoi.
Phong Nha weather at a glance
The park has no weather station of its own. The table uses official long-run averages for Tuyen Hoa, about 25 km away and inland like Phong Nha, from the Vietnam Institute for Building Science and Technology, as published in Wikipedia's climate table. Dong Hoi, on the coast about 40-45 km away, is a little drier and sunnier.
| Month | High | Low | Rain | Rain days | Sunshine (h/month) |
|---|---|---|---|---|---|
| January | 21.8°C | 15.7°C | 47 mm | 15 | 64 |
| February | 23.1°C | 17°C | 40 mm | 13 | 63 |
| March | 26.4°C | 18.9°C | 52 mm | 13 | 98 |
| April | 31°C | 21.8°C | 75 mm | 11 | 142 |
| May | 33.8°C | 24.1°C | 155 mm | 12 | 197 |
| June | 34.2°C | 25.6°C | 130 mm | 10 | 204 |
| July | 34.2°C | 25.5°C | 143 mm | 10 | 209 |
| August | 33.3°C | 24.8°C | 267 mm | 15 | 173 |
| September | 31.2°C | 23.5°C | 501 mm | 17 | 123 |
| October | 28.1°C | 21.6°C | 655 mm | 20 | 97 |
| November | 25°C | 19°C | 224 mm | 17 | 71 |
| December | 22°C | 16.3°C | 84 mm | 15 | 54 |
The year totals about 2,370 mm of rain, and September to November bring nearly 60% of it. Notice the winter: December to March have 13 to 15 rain days a month on only 40 to 84 mm, the sign of persistent drizzle, and only about 55 to 100 hours of sun a month. Phong Nha runs on the central-coast calendar, like Hue, about 210 km south.
Spring, March to May: the sweet spot
After the winter drizzle, March and April warm up to 26-31°C, and the countryside is green. By May, highs reach 34°C. Every cave tour runs in this period, from the show caves to Son Doong, Hang En and Tu Lan, and the rivers are calm. It is the best all-round time for caves, trekking and cycling the valleys.
Summer, June to August: hot, dry and windy
From May to August, the south-west monsoon crosses the mountains from Laos and arrives as a hot, dry wind, known locally as gio Lao. Average highs are 33-34°C, humidity can fall as low as 28% on strong wind days, and Dong Hoi has recorded 43°C in April and 42°C in May. It is the ideal time for the cool caves and for swimming at the Dark Cave and in the rivers; hike early, and spend midday underground. August brings the first heavier rain.
Summer can still bring surprises: in July 2026, heavy rain upstream in Laos turned the Son River muddy, and swimming and kayaking were suspended for a time while the caves stayed open.
The flood season, September to November
This is when Phong Nha gets most of its rain: about 500 mm in September, 655 mm in October and 224 mm in November at Tuyen Hoa. Rivers rise quickly, and floods can last up to a week. Big floods are regular events:
- October 2020: Quang Binh province received about 550 to 1,200 mm of rain from 6 to 13 October, then more than 1,000 mm at Van Trach in four days, and floods killed 19 people in the province.
- October 2024: after Storm Trami, flooding submerged thousands of homes, and from 29 October the park suspended all cave tours, forest treks and river activities, as VnExpress reported.
- Autumn 2025: a series of storms from late September disrupted cave tours across the park.
Oxalis, which runs the adventure caves, closes its tours from mid-September to the end of October. Phong Nha Cave and Paradise Cave stay open daily in principle but close whenever storms or high water arrive. Vietnam's national tourism board advises avoiding October to December for caves.
Winter, December to February: cool and drizzly
Winter is cool and grey. Highs are 22-23°C and lows about 16°C, with frequent drizzle and little sunshine. The show caves are open, and adventure tours restart from about mid-November or December: Oxalis runs Hang En from December and Tu Lan from mid-November, and suggests extra warm clothes from mid-November to mid-March. Son Doong starts in January.
Cave seasons at a glance
| Cave or tour | Season |
|---|---|
| Phong Nha Cave (boat) and Paradise Cave | Daily, year-round, except in storms and floods |
| Son Doong expedition (6 days, US$3,000) | January to end of August; 2027 and 2028 fully booked |
| Hang En (2 days) | From December into late summer |
| Tu Lan | From mid-November to mid-September |
| Oxalis tours overall | Closed from mid-September to end of October |
Our Phong Nha caves guide ranks the caves by cost and difficulty, and our Paradise Cave and Phong Nha Cave page covers the show caves.
What the weather means for your trip
Choosing the month. March to May is best; June to August for swimming and caves in the heat; December to February for quiet show caves in cool weather; avoid September to November if you can.
Planning. Our day trips from Phong Nha guide sequences the caves and valleys, and our where to stay in Phong Nha guide explains the village, riverside and farmstay options. Phong Nha is about four hours by road from Hue; see our Hue to Phong Nha guide.
Limitations
The table uses official long-run averages for Tuyen Hoa, about 25 km from Phong Nha, as reproduced on Wikipedia; conditions in the park, especially in the mountains, differ. Oxalis's own pages give slightly different season dates for some caves, and season dates can change. Flood timing and severity vary a lot from year to year.
Workaround: use this page to choose the season, check Oxalis and the park's notices before booking, and keep flexible plans from September to November.