Vietnam Weather by Month: 14°C Nights in Hanoi, Monsoon in Da Nang in October — Wet Seasons That Run Backwards

Vietnam suggests T-shirts and flip-flops, and in Ho Chi Minh City that holds: January days reach 31.9°C. But Hanoi's January averages 21.1°C by day and 14.1°C at night, and with damp air and many buildings unheated it feels colder than the numbers. In the same January you'll see puffer jackets in Hanoi and vests in Saigon.

Rain is the bigger trap. Vietnam's wet season isn't one season: the north and south get their rain from May to October, the central coast (Da Nang, Hoi An, Nha Trang) from September to December. When Da Nang is at its best in April–May, Saigon's rains are starting; when Saigon is at its best in December–January, Da Nang is still wet. Ask not "when is Vietnam good?" but "where is good that month?"

It comes down to wind direction. The May–October south-west monsoon soaks the south, while the central coast sits in the lee of the Truong Son mountains. From September to December the wind swings round to the north-east and dumps sea moisture straight onto the central coast. Da Nang's October average of 491 mm is more than Seoul gets in its wettest month, July (313 mm).

Hanoi's temperature curve is Seoul's shifted upwards: winters like Seoul's late autumn, summers hotter than Seoul's. June averages 16.3 days above 33°C, and May–September bring 220–430 mm of rain a month. January–March often means days of fine drizzle (mua phun), grey skies and permanently damp pavements.

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Hanoi's autumn (October–November) is Vietnam's most underrated season: 26–28°C days and far fewer wet ones.

Da Nang, Korea's favourite Vietnamese beach city, is most balanced in March–May: 27–32°C days, the year's lowest rainfall (62–77 mm a month), and before the June–August heat (19.2 days above 33°C in June). June–August is still dry enough for a pool-and-beach trip. Nha Trang follows a similar pattern, but its January rain (85 mm) is half Da Nang's (165 mm), so its season runs a little longer.

In the south, seasons are about rain, not temperature. Saigon's monthly rain is 17–73 mm from December to March and jumps to 240–370 mm from May to October. But southern wet-season rain mostly arrives as an hour or two of afternoon downpour, so a morning-heavy itinerary survives it. The toughest months are actually March–April at the end of the dry season: March averages 28.2 days above 33°C.

Phu Quoc is even starker: 41 mm in February becomes 421 mm in July, ten times as much. During the May–October south-west monsoon, the beaches on the island's west side often get waves too rough for swimming. Late November to March is Phu Quoc's season.

Clothing advice is for Hanoi; Da Nang and Saigon are T-shirt cities all year, so only their temperatures are listed. For the south and centre, one thin long-sleeve layer for arctic air-conditioning on buses and indoors is enough.

1. Tet (Lunar New Year): shops and restaurants close for about a week and transport sells out. Tet 2027 falls on 6 February.
2. Central-coast storms and floods (September–December): as above, Da Nang, Hoi An and Nha Trang are safer outside this window.
3. End-of-dry-season heat in the south (March–April): split Saigon walking tours into mornings and evenings.
4. Northern winter haze (December–March): Ha Long Bay is often misty, so the views may not match the brochures.

• Period and source: daily values from Open-Meteo's historical weather data (ERA5 reanalysis), 2016–2025, averaged by month at each city-centre coordinate.
• Versus official normals: reanalysis temperatures usually land within 1–2°C of station normals, but downpours get smoothed out, so monthly rain totals come out lower and rainy-day counts slightly higher.
• Rainy day: at least 1 mm of precipitation. Reanalysis picks up even light showers, so counts run high — especially in the tropics, where monthly millimetres are the better guide. Most tropical rain is an hour or two of downpour, not a washed-out day.
• Best months: a first pass from temperature, rainy days and humidity, then adjusted for seasonal factors such as Tet and the central-coast storm season. It is a judgement call.