The monsoon map: which Vietnamese coast is trainable in which month

When we published the 2027 calendar we said that Vietnam has three climates, not one, and that each camp sits in the month its coast is best in. That article gave the logic. It did not give the numbers, and on this subject a number you cannot check is worth nothing, because the first thing a careful athlete does is open a weather site and look at "Vietnam in July". So here are the numbers, site by site and month by month, with where each one comes from.

The short version is in the title. Vietnam is 1,650 km long and the monsoon reaches its coasts at different times: the south is wet from May to October, the central coast is dry then and drowns in October and November, the north has a real summer wet season and a dry, cool autumn. A camp "in Vietnam in October" means nothing. A camp in Ninh Binh in October and a camp in Da Nang in October are two different countries.

Where the figures come from

Two kinds of figures, and we do not mix them without saying so.

For Da Nang and Nha Trang, and for Hanoi and Ho Chi Minh City as the anchors of the north and the south, the figures are the official 1991 to 2020 climate normals of the Vietnam Meteorological and Hydrological Administration, as published by the World Meteorological Organization's World Weather Information Service and read there on 29 September 2026. Those are the thirty-year station averages the country's own forecasters use.

For Ninh Binh, Quy Nhon, Phan Thiet, Phu Quoc and Da Lat, which have no station in that service, the figures are the ERA5 reanalysis of the European Centre for Medium-Range Weather Forecasts, averaged over the same thirty years, 1991 to 2020, from the Open-Meteo archive, read on the same day. Reanalysis is a model fitted to observations, not a thermometer, and we measured its bias against the two stations we do have: on this coast it reads daytime highs 1 to 2 °C cooler than the station and it smooths the extremes of rainfall. Read the reanalysis rows, marked with an asterisk, as a floor for the heat and as the shape of the rain rather than its exact height.

Sea temperatures are monthly averages of daily sea surface temperature from January 2023 to August 2026, from the Open-Meteo marine archive, at the coast in front of each base. Not a thirty-year normal, but recent, and the same source for every site.

Rain, month by month

Monthly rainfall in millimetres. An asterisk marks a reanalysis row.

Read the table down a column and the country splits in front of you. In July, Da Nang gets 92 mm on 12 rain days and Nha Trang 45 mm on 9, while Phu Quoc gets 408 mm and Hanoi 300. In October it flips: Hanoi is down to 126 mm on 10 days, and Da Nang is at 658 mm on 21 days, its wettest month by far, with the typhoon season open on that coast. The south sits in between: Ho Chi Minh City and Phan Thiet are dry from December to April, then take 200 mm a month from May to October.

Two rows deserve a closer look. Nha Trang is the dry anomaly of the whole country: a coast sheltered from the south-west monsoon by the mountains behind it, and too far south to take the north-east monsoon before October. February to August, its wettest month is 78 mm on 9 days. That is why it carries two camps. And Phu Quoc is not the dry island its brochures describe: around 2,700 mm a year on the reanalysis, more than Da Nang's 2,400 on the station, with a short dry season from December to March. Its March week is in that season. Its June would not be.

Heat, month by month

Average daytime maximum in °C. For the asterisk rows add 1 to 2 °C to get what a thermometer at the station would read.

The temperature alone does not tell you how a session feels; the humidity does. In Da Nang the reanalysis puts the average relative humidity at 77 to 79 percent in June, July and August against 86 to 87 in the winter months, which is why the July heat there is a dry-ish, radiant 35 °C rather than a steam bath. Quy Nhon in July and August has the driest air on the whole coast, around 72 percent, and Da Lat the wettest in September, over 90 percent under a 22 °C sky. February in Da Nang is 26 °C in the day and 20 at night; February in Ninh Binh is 22 and 16, with the grey northern drizzle that keeps Hanoi under cloud for most of the month, which is exactly why the north is in October on our calendar and not in February.

The sea, month by month

Average sea surface temperature in °C, January 2023 to August 2026.

The surprise for a European is at the top of the range, not the bottom. Nowhere south of Da Nang does the sea drop under 24 °C in any month, so a wetsuit is dead weight in your bike box for every camp except, at a stretch, February in Da Nang. The real limit is the other way: World Triathlon caps time in the water at twenty minutes for a race swim once the sea is between 30.1 and 32 °C, and Phu Quoc in April and May, Phan Thiet in May and Da Nang in August are all in that band. A long open-water session in 31 °C water is a heat exposure, not a recovery swim, which is why on those weeks the long swim goes in at dawn, before the surface layer has warmed, and why the sea sessions are built in sets with time out of the water rather than as one continuous hour.

Temperature is not the only thing that closes a coast. The Mui Ne coast at Phan Thiet has two wind seasons, a north-east onshore wind from December to March that makes it a kitesurfing capital and a south-west offshore wind in July and August; the calm swimming window is April and May, and September and October, which is why the sea-swim camp is in April. Phu Quoc's west coast, where the resorts are, faces the south-west monsoon head-on from May to September. And the central coast from Da Nang to Nha Trang turns in early September, when the typhoon season opens and the swell arrives; from then until January the beaches at Da Nang fly red flags.

What the map says, camp by camp

• February, Da Nang. 22 mm on 7 rain days, 26 °C in the day, sea at 24 °C. The one month on this coast where all three disciplines run at full value, before the heat builds.
• March, Phu Quoc. The last month of the island's short dry season: 65 mm, 29 °C, sea at 30. By April it is 128 mm and by May 332. The week is where it is because of that column.
• April, Phan Thiet. 67 mm, 31 °C, and the only calm window between the two wind seasons. Sea at 29 to 30 °C: morning swims, in sets.
• May, Nha Trang. 78 mm on 9 days, 32 °C, sea at 30. The most dependable week of the year, on the driest coast in the country.
• June, Quy Nhon. 87 mm, 33 °C, and the driest air of the summer on the central coast. Warm, not yet the July peak.
• July, Da Nang. 92 mm on 12 days, 35 °C, sea at 30 to 31. The heat is the product. Advanced only.
• August, Nha Trang. 54 mm on 10 days, 33 °C. The endurance version of the heat week, on the coast that stays dry when the rest of the country does not.
• September, Da Lat. 293 mm on the reanalysis, 23 °C, 1,500 m up. It rains in the afternoon almost every day, which is why the week is one long morning session and a free afternoon, and why the coast, at 32 °C and with the typhoon season opening, is not where we are that month.
• October, Ninh Binh. 159 mm, 28 °C in the day and 22 at night, humidity finally down. The only real autumn in the country, while Da Nang is under 658 mm.

There is no month in which every coast is trainable, and there is no coast that is trainable every month. Nha Trang comes closest, with seven dry months from February to August. That is the whole reason the calendar has nine camps in seven places: not variety, arithmetic.

How to use this

If you are choosing a week, read the column for your month and pick the coast that is dry in it, then read the sea row and decide whether you want to swim in it. If you are checking us, the sources are named above and the station normals are public; open them and compare. And if a weather site tells you it rains in Vietnam in July, it is right, and it is talking about a coast we are not on.