01 Four genuine seasons
The data come from the Vietnam Institute for Building Science and Technology's station, for the city centre. The annual mean is 23.9 °C, with 1,670.1 millimetres of rain over almost 148 days, a mean relative humidity of 80.7% and 1,488.5 hours of sunshine a year.
That last figure is the one to hold on to: 1,488 hours of sunshine a year is very little for this latitude. To give you a sense, it is less than half what a Gulf capital receives. And it is not evenly distributed, not remotely.
02 The spring without light
March has 45.5 hours of sunshine in the whole month. February, 48.1. Between them they add up to 93.6 hours, that is, a little over an hour and a half a day on average. The official description of spring — March and April — speaks of "some amounts of drizzle and less sunshine", and it understates the case.
It is not that it rains a lot: March delivers 47 millimetres. It is that it rains a little over many consecutive days and the sky never opens.
The numbers say it plainly: March has 15.9 days with precipitation but only 47 millimetres, which works out at about three millimetres per rain day. That is persistent drizzle, not downpour. And relative humidity reaches 84.5% in March and 84.7% in April, the year's highest figures.
03 The monsoon summer
From May to September the opposite arrives: heat, humidity and real rain. August is the wettest month with 309.4 millimetres over 16.5 days; July follows with 280.1 and June with 253.3. The five months from May to September add up to 1,256.5 millimetres, 75% of the whole year.
The temperature keeps pace: July has a mean of 29.4 °C and highs of 33.4, and June is much the same. The all-time record for the series is 42.8 °C, measured in May 1926. At that temperature with humidity above 80%, any outdoor plan between eleven and five is questionable.
04 Autumn, and that is that
The good window is October to December, and there is not much room for argument. November is the year's best month: 21.9 °C mean, 66.7 millimetres over 6.8 rain days and 77.1% relative humidity, the second lowest of the twelve months.
December is the driest of all — 20.2 millimetres over 5.2 days — and the coolest of the window, with a mean of 18.3 °C and lows of 15.8. October is warmer and considerably wetter, at 140.7 millimetres, but it has 150.3 hours of sunshine, twice January's.
January deserves a separate mention, because it deceives. It is cool (16.6 °C mean, the coldest month) and dry (22.5 millimetres), which on paper sounds perfect. But it has only 68.7 hours of sunshine, and the city's record low sits here: 2.7 °C, measured on 12 January 1955. Bring a layer.
Summed up in one line: come in November. And if you cannot, in December or October. What to avoid above all is not July's heat, which is manageable if you organise around it, but the spring: two consecutive months without seeing the sun ruin a city that is looked at, above all, from the street.
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G Da ToledoIt only rains fifty-three days a year here.
26D TashkentAugust brings two millimetres of rain and February seventy-two.
David Stanley Ashgabat