The year on the Quảng Nam coast, month by month
The figures are Đà Nẵng's, this coast's reference station, some 30 kilometres north of Hội An: 2,205 millimetres of rain a year over 139.1 days and 2,162.6 hours of sunshine. The scoring crosses three things: how much water falls, how much light there is and how hot it gets.
There are destinations where choosing the month is a matter of nuance and others where it is the most important decision of the trip. Vietnam's central coast belongs to the second group, and a single subtraction shows it.
In October 628.0 millimetres of rain fall. From January to August, eight months in a row, 563.2 fall in total. A single month beats the first two-thirds of the year combined, and it is not even an isolated case: November adds another 448.2 and September 350.7.
01 The sum that decides the trip
The annual total is 2,205 millimetres spread over 139.1 days. That is a high amount, but the striking thing is the distribution. From September to December 1,645.3 millimetres fall: 75 % of the year in four months.
Rainy days follow the same curve. March has 4.8 rainy days and February 5.6. October has 20.0 and November 20.3, the year's maximum. Put another way: in March it rains one day in six and in November two days in three.
And the light follows. The sunniest month is May, with 246.7 hours; the least, December, with 94.8. Between them there is a difference of two and a half hours a day, which on a week-long trip shows in everything.
02 The temperature barely moves
What does not change is the thermometer. The monthly mean runs from 21.5 degrees in January to 29.4 in June: less than eight degrees of range across the whole year. The annual mean is 25.9.
Average highs run from 25.0 degrees in January to 34.5 in June, and lows from 19.3 to 26.0. There is not a single cold month, nor one in which the average low drops below 19 degrees. Records exist — 41.5 in May, 9.2 in December — but they are very rare exceptions.
The practical consequence is direct: here you do not choose the month by temperature, because temperature gives you no information. You choose by water and by light, and those two go together.
03 Why it rains at the end of the year
The calendar surprises anyone arriving with the general idea of monsoon Asia, where rain usually concentrates in summer. Here the opposite happens: June and July are dry months and October is the month of the deluge.
The reason is the orientation of the coast and the mountain barrier behind it. In summer the dominant flow comes from the south-west and reaches this side already emptied after crossing the range. In autumn the flow changes direction, comes in off the sea loaded with moisture and hits the relief head-on.
On top of that comes the typhoon season, which on this coast runs from September to December. Not every year brings one, but the risk is part of the calendar and explains why those months also concentrate the most intense rainfall episodes.
04 What happens when the river rises
The rain does not stay where it falls. Between 65 % and 70 % of the annual flow of the province's rivers passes between October and December, and the ground that has to absorb it is a very flat, very low plain.
The result is annual floods. It is not an exceptional accident: it is a feature of the calendar, as predictable as the dry season. The old houses of Hội An's centre are built with that in mind, with a commercial ground floor and a timber upper floor to which anything that cannot get wet is carried.
If you travel between October and December, reckon with it. That does not mean it is impossible: it means accepting that on some days the street is a canal, that road access can be cut and that plans on the plain and the river are decided in the morning.
The year's four stretches
23.6, 25.0 and 35.3 millimetres over fewer than six days each month, with sunshine climbing from 146.0 to 208.6 hours and highs from 26.2 to 31.0 degrees. The only stretch with little rain and heat that is still manageable.
From 81.1 to 92.5 millimetres over eight or nine days, with 242 to 247 hours of sunshine. Highs of 33.3 to 34.5 degrees and records reaching 41.5. Still the dry season, but the heat rules.
141.2 and 350.7 millimetres: rain multiplies by four from one month to the next. The heat eases to 33.9 and 31.8 degrees. August is still viable; September is not.
628.0, 448.2, 218.4 and 81.9 millimetres, over 20.0, 20.3, 18.7 and 12.0 days. Sunshine falls to 143.4, 117.7, 94.8 and 131.9 hours. This is the typhoon season and the season of the river's floods.
05 Eight dry, very hot months
The other half of the year is the good one, with one important caveat. From February to April the figures are unbeatable: 23.6, 25.0 and 35.3 millimetres over fewer than six days each month, with sunshine climbing from 146.0 to 208.6 hours and highs from 26.2 to 31.0 degrees.
From May to July it still rains little, but the heat changes the calculation. Average highs reach 34.5 degrees in June and 34.4 in July, with records of 41.5 and 40.6. At that temperature, walking around an old town with no shade at midday stops being a plan.
Humidity, which stays high all year, worsens the sensation. It runs from 75.8 % in July to 85.4 % in December, so not even in the driest month does it drop below three-quarters. June's 34 degrees are not the same as 34 degrees in a continental climate.
06 How to choose the month
If you can go only once, go in March: 25.0 millimetres of rain over 4.8 days — the year's fewest — 182.3 hours of sunshine and average highs of 28.3 degrees. It is the exact crossing point between little rain and heat that is still reasonable.
February and April work almost as well: 23.6 and 35.3 millimetres, over 5.6 and 5.4 days. February has less light — 146.0 hours — and April is already pushing with highs of 31.0 degrees, but both fall comfortably within the good window.
And if your only option is the last quarter, go knowing what it is: 20 rainy days a month, under five hours of sunshine a day and a river that overflows regularly. In exchange you will see the town in its most characteristic state, which is also the one that explains how it is built.
