Hanoi has four real seasons, and the difference between them is big. Here is what each month is like.
The best time to visit Hanoi is October and November. Days are warm but not hot, at 25 to 29°C (77 to 84°F), rain is at its lowest for the year, and the humidity eases.
March and April are not a good time to visit. They are warmer and more humid than autumn, with 13 to 14 rainy days and much more grey sky.
December to February is cool and mostly dry, with daytime highs of 20 to 22°C (68 to 72°F). It can feel cold indoors, because almost no building has heating. The bigger problem is the air: winter is when air quality in Hanoi is at its worst.
June to August is not a great time to visit. Highs of 33 to 34°C (91 to 93°F), humidity to match, rain on more than half the days, and storms heavy enough to flood streets. Avoid it if you have a choice.
Not the best time to visitSummer monsoon rainsUrban flooding
Temperatures begin to moderate in September, and humidity drops; it's a good shoulder-season month before the main tourist influx.
SCORE BY MONTH
Unlike most of the region, the temperature here changes a lot through the year.
The coldest month, and the one with the worst air of the year. Dry, but grey more often than sunny. Bring a jacket.
Cool, damp and often grey, with drizzle that is closer to mist than rain. Tet usually falls in this month or late January. Air quality is still poor.
Warming up, but humid at over 80%. This is the damp spring period, when moisture condenses on floors and walls. The air starts to improve.
Much cleaner air than in winter, but humid and wet enough to plan around. Comfortable for walking on a dry day.
Hot, with the summer rains starting. Storms arrive in the late afternoon.
Hot and wet, and the nights stay warm enough that the heat never really lets go.
The hottest and wettest month, and the streets flood after the heavier storms.
Much like July: hot, humid and stormy, with flooding possible. Hotel rates are at their lowest.
The heat falls back, the rain eases and the last summer storms thin out. Late September is the better half.
One of the two best months: dry, with clear light and low humidity. Reliable weather for day trips to Ha Long Bay or Ninh Binh.
The other best month, and cooler, with comfortable evenings. Air quality starts to worsen late in the month.
Dry and cool, and the driest month of the year. The grey skies and the bad air both come back.
Airfare here differs by season, and not always in step with the weather. These are the cheapest fares held on Hanoi's busiest nonstop routes, each measured against its own typical month.
Measured on Bangkok, Da Nang, Ho Chi Minh City, New Delhi, Seoul to Hanoi: two domestic routes, the busiest international one, and the long-haul routes that carry the most traffic. Each route is compared against its own typical month, so a long flight and a short one count equally and what is left is the season. Cheapest fares only, and airfare only, not the cost of the trip.
Hanoi is far enough north to get real seasons. Winter highs are around 20°C (68°F) and summer highs reach 34°C (93°F), a range you will not find in Da Nang or Ho Chi Minh City.
Winter, December to February. Cool and dry, often grey, with drizzle rather than rain.
Spring, March and April. Warmer and more humid than autumn, with mist common in March and rain on 13 to 14 days a month.
Summer, May to September. Hot, humid and stormy, with the heaviest rain of the year from June to August.
Autumn, October and November. Dry, warm and clear, and the best two months of the year.
December is dry, with the fewest rainy days of the year, and cool.
January and February are colder still, and more humid. It can feel cold because homes and hotels rarely have heating, so a cheap room in January is unpleasant.
Air quality is the real winter problem. From December to February the air over Hanoi is at its worst, and there are days when haze covers the city and the sky never clears. If anyone in your group has asthma, check the reading before planning a long day outside. The Hanoi guide shows the current level.
The rainy season is May to September, and June, July and August are the worst of it. Rain falls on 16 to 18 days a month and usually arrives as an afternoon or evening storm.
Storms can be heavy enough to flood streets, especially from July to September. The Old Quarter drains slowly, and flooding slows the traffic. Water clears within a few hours.
Summer is also the cheapest time to stay. If you came for the food and the museums, the rain matters less. If you came for Ha Long Bay, it matters a lot.
Tet is the Vietnamese new year and the biggest holiday of the year. It falls in late January or February and the date moves. The Vietnam guide lists the upcoming dates.
Many small restaurants and shops close for several days, and Hanoi empties as people travel to their home towns. Trains, buses and domestic flights sell out weeks ahead and cost more.
Go then if you want to see the city at its most festive and you accept that many of the places you planned to eat are closed. Avoid it if you need shops and transport to work normally.
Hanoi is the base for three big trips, and they have different best seasons.
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October. It is dry, warm, and the humidity has eased. November is a close second and a little cooler. Both are far more comfortable than summer and have better air than winter.
Cold for the tropics, not cold in absolute terms. December to February highs are 20 to 22°C (68 to 72°F) and lows can reach 14°C (57°F). Heating is rare, so indoors often feels colder than outdoors. A warm layer and a jacket are enough.
May to September. June, July and August are the wettest, with rain on 16 to 18 days a month. It normally falls as an afternoon storm rather than all day.
June to August. It is the hottest and wettest part of the year, so hotel rates fall. Avoid the week of Tet, when domestic travel pushes prices up.
In winter, yes. December to February is when the air is at its worst, and there are days bad enough to keep sensitive people indoors. Summer has the cleanest air of the year.