Vietnam Rainy Season by Region (Hanoi, Hoi An, Ho Chi Minh City)

Vietnam is roughly 1,650 kilometres from top to bottom, which is about the distance from London to Athens, and almost every article about its rainy season treats it as one country with one wet season. That single mistake is responsible for most of the ruined trips.

The country has three rain regimes, and two of them are close to opposite. There is a month in which the driest of the three cities below is the one that will be underwater eleven weeks later. If you take one thing from this page, take that: in Vietnam, the answer to when it rains is meaningless until you say where.

The figures below are monthly averages from Weather Spark, taken from the same source for all three cities so that they can actually be compared. A great many published comparisons quietly mix stations and periods, which is how you end up with tables that contradict each other.

The north: Hanoi and the summer monsoon

Hanoi runs on the classic southwest monsoon. Rain arrives in May, peaks in high summer and is finished by early autumn. Average rainfall by month, in inches: January 0.5, February 0.5, March 1.2, April 2.1, May 5.0, June 6.3, July 8.0, August 8.9, September 6.8, October 3.3, November 1.8, December 0.6.

August is the wettest month at 8.9 inches, or about 226 mm, with 17.2 days of measurable rain. June through September alone carry roughly two thirds of Hanoi's annual total. The wetter season is dated from 3 May to 6 October, and the drier season fills the remaining 6.9 months.

The practical shape of a Hanoi summer is heat and humidity punctuated by heavy afternoon storms, not continuous rain. Seventeen rain days in August still leaves fourteen without. What actually spoils plans in the north in that window is not Hanoi itself but the mountains: Sapa, Ha Giang and the northern loops sit on saturated slopes, and the road closures and landslide risk there follow the same logic as anywhere else in monsoon Asia.

The north gets typhoons too, and they arrive on a different schedule from the ones that matter further south. Storms that track west across the northern part of the basin tend to come ashore around the Gulf of Tonkin between July and September, which puts Ha Long Bay, Hai Phong and the northern coast at their highest risk in exactly the months the central coast is quiet. The visible sign for a traveller is usually the cruise boats: Ha Long suspends sailings when the warnings go up, and that decision is made on the day rather than in advance.

The other half of the northern year is the part visitors underestimate. From December to February Hanoi is genuinely cool, with January and February averaging half an inch of rain, but that dryness comes with weeks of low grey drizzle and overcast that photographs badly and hides Ha Long Bay. Dry does not mean sunny in the north.

Central Vietnam: Hue, Da Nang and Hoi An

This is where the standard advice falls apart. Da Nang's monthly rainfall, in inches: January 1.6, February 0.5, March 0.6, April 1.1, May 2.4, June 2.5, July 2.3, August 4.7, September 11.5, October 17.9, November 12.0, December 5.7.

Read July across the three cities. Hanoi is at 8.0 inches, Ho Chi Minh City is at 6.3, and Da Nang is at 2.3. In the middle of what everyone calls the Vietnamese rainy season, the central coast is the driest place in the country by a factor of three.

Now read October. Hanoi has fallen to 3.3 inches and Ho Chi Minh City sits at 6.5. Da Nang is at 17.9 inches, roughly 455 mm, with 18.3 rain days. September, October and November together account for about two thirds of Da Nang's entire annual rainfall, compressed into three months. Its wetter season is dated 16 August to 13 December, which is almost exactly the window most travellers have been told is fine.

The reason is geography rather than bad luck. The Truong Son range runs down the country's spine, and in autumn the wind reverses to come in off the sea from the northeast. That moist air hits the mountains and is forced upward directly over the narrow coastal strip where Hue, Da Nang and Hoi An sit. The same range that shelters the central coast from the southwest monsoon in July is what wrings the rain out over it in October.

Typhoons stack on top of that. The western Pacific storm track drifts south as the season runs on, so the landfalls that hit Japan and the northern Philippines in August tend to be hitting central Vietnam by October and November. That is why the region's serious flood events cluster in exactly those months, and why Hoi An's old town, which sits low on the Thu Bon river, floods often enough that shops there keep their stock on upper shelves as a matter of routine rather than emergency.

None of this makes the central coast a place to avoid. It makes it a place to time. Hoi An in June is close to ideal and almost nobody warns you about it, because the warnings are written for a rainy season that belongs to a different part of the country.

The south: Ho Chi Minh City and the delta

The south is the most forgiving of the three and the easiest to plan around. Ho Chi Minh City's monthly rainfall, in inches: January 0.2, February 0.2, March 0.4, April 1.3, May 4.3, June 6.2, July 6.3, August 5.8, September 6.5, October 6.5, November 2.8, December 0.8.

The wet season is dated 8 May to 11 November, and roughly 86 per cent of the annual total falls inside it. What matters more is the shape of that rain. September and October are the wettest months at 6.5 inches, but spread over 16.6 and 16.5 rain days respectively, which works out at well under half an inch on a typical wet day. Compare that with Da Nang in October: 17.9 inches over 18.3 days, close to an inch per rain day.

That is the difference between a downpour you wait out under an awning and a day that is simply gone. Southern rain in the wet season is typically a heavy burst in the late afternoon or overnight, lasting well under two hours, after which the city carries on. Mornings are usually usable, which is why the standard advice to move early works better in the south than anywhere else in Vietnam.

The south also sits close enough to the equator that direct typhoon landfalls are rare, since a tropical cyclone needs the Earth's rotation to spin up and that effect weakens sharply near the equator. The delta's real water problem is not storms but the annual river flood and, increasingly, saltwater intrusion in the dry months. Neither is a travel concern in the way an October typhoon on the central coast is.

Which month to pick, and what to avoid

Put the three columns side by side and the planning rules fall out on their own.

• June and July: good for the central coast and the beaches around Da Nang and Hoi An, wet in Hanoi and the south, and the single most misunderstood window in the country.

• October and November: good in Hanoi, workable in the south, and the worst possible time for Hue, Da Nang and Hoi An. If your itinerary has all three regions in this window, the central leg is the one to shorten.

• December to February: dry almost everywhere, cool in the north with grey overcast, pleasant in the south, and still carrying the tail of the central wet season into December.

• March and April: the closest thing to a nationwide good window, dry in all three regions before the southwest monsoon starts.

The itinerary that causes the most trouble is the classic three week north to south run in October, because it puts the traveller on the central coast at the exact peak. Reversing the direction, or moving the central leg to the start or end of the trip, costs nothing and removes most of the risk.

One last note on averages, which is the caveat that applies to every number on this page. A monthly mean of 17.9 inches does not describe a typical October. It describes the middle of a range that includes quiet years and years in which a single week delivers most of that total. Plan by the averages, then check the forecast in the fortnight before you travel, because on the central coast in autumn the difference between the average and the event is the whole story.

Country level climate summaries for Vietnam are published by Weather Spark here: https://weatherspark.com/countries/VN

The official Vietnamese tourism board's weather and climate overview is here: https://www.vietnam.travel/things-to-do/weather-and-climate-vietnam

The Japan Meteorological Agency publishes western Pacific tropical cyclone tracks and five day forecasts in English here: https://www.jma.go.jp/en/typh/

Satellite imagery on this page is from NASA Worldview and is in the public domain.

More on typhoons and storms

• Seven Years in the Philippines and I Never Saw a Typhoon Like the Ones That Reach Korea. Here Is Why Storms Often Leave Stronger Than They Arrive.
• No, Thailand's Flooding Is Not From Typhoon Dolphin — and the Difference Matters
• Laos in the Rainy Season (Rainfall by Month, Route 13, What Actually Closes)