Vientiane weather in September
In September, Vientiane has daytime highs averaging 30 °C, nights around 24 °C, with 24 wet days. Figures are 1991–2020 climate normals.
- 29.6°C Average high
- 23.7°C Average low
- 24days Wet days
- 306mm Rainfall
- 12h Daylight
Daily temperatures through September
How September develops
Averages for the first, middle and last part of the month, from daily 1991–2020 normals. Chance of rain is the share of years in which that calendar day recorded more than 1 mm.
| Days | Avg high | Avg low | Chance of rain |
|---|---|---|---|
| 1–10 September | 29.6 °C | 23.8 °C | 93 % |
| 11–20 September | 29.5 °C | 23.8 °C | 83 % |
| 21–30 September | 29.7 °C | 23.6 °C | 67 % |
- Rain is most likely over days 1–10 of September (93 % of days) and least likely over days 21–30 (67 %).
What to expect
| Measure | Typical September | Share of the month |
|---|---|---|
| Days above 25 °C | 30 of 30 | 100 % |
| Days above 30 °C | 13 of 30 | 44 % |
| Days below 0 °C | 0 of 30 | 0 % |
| Days with more than 1 mm rain | 24 of 30 | 81 % |
Conditions in September
| Measure | Average |
|---|---|
| Mean temperature | 26 °C |
| Record high (1991–2020) | 34 °C |
| Record low (1991–2020) | 20 °C |
| Relative humidity | 86 % |
| Wind speed | 8.0 km/h |
| Cloud cover | 80 % |
September compared with the months around it
| Month | Avg high | Rainfall | Cloud |
|---|---|---|---|
| July | 29.9 °C | 375 mm | 92 % |
| August | 29.6 °C | 409 mm | 92 % |
| September | 29.6 °C | 306 mm | 80 % |
| October | 29.3 °C | 100 mm | 57 % |
| November | 28.6 °C | 21 mm | 37 % |
See all twelve months for Vientiane
- September is the 7th warmest month here.
- It is the 9th driest month of the year.
- It ranks 9th for least cloud cover.
- Days last about 12 hours from sunrise to sunset.
- It rains on 24 of 30 days — 81 % of the month.
- Nights are about 5.9 °C cooler than the middle of the day.
- The hottest September day on record since 1991 reached 34 °C, 3.9 °C above the usual daytime high.
QuestionsSeptember in Vientiane, answered
How warm is Vientiane in September?
Daily highs average 30 °C and nights fall to about 24 °C, a spread of 5.9 °C between afternoon and dawn. That makes September the 7th warmest month of the year here.
Does it rain much in Vientiane in September?
September averages 306 mm of rain, spread over about 24 of the 30 days — 81 % of the month. Cloud cover averages 80 % of the sky.
How long are the days in September?
Vientiane averages 12 hours between sunrise and sunset in September. Day length is computed from latitude and date, so it is exact rather than modelled — but it says nothing about how much of that time is sunny.
Data sources and method
- ERA5 / ERA5-Land reanalysis — Copernicus Climate Change Service (C3S), ECMWF. Copernicus Licence
- Open-Meteo — Open-Meteo.com. CC BY 4.0
- NOAA OISST v2.1 — NOAA Physical Sciences Laboratory. Public domain
- GeoNames — GeoNames.org. CC BY 4.0
- Normal period
- 1991–2020
- Dataset version
- era5-1991-2020-scores1.1
- Last processed
Measured values come from ERA5 reanalysis and are reproduced unchanged. Calculated by us: daylight hours, beach and comfort scores, monthly rankings, threshold day counts, chance of a wet day by date, ten-day averages within the month. Full formulas are on the methodology page.
Contains modified Copernicus Climate Change Service information 2026. Neither the European Commission nor ECMWF is responsible for any use that may be made of the Copernicus information or data it contains.