Climate averages 1991–2020
Vientiane weather
in September.
A hot, very wet month: the joint 7th warmest and the 9th driest of the year.
Long-term climate patterns, not a forecast for a particular trip.
September is a hot month in Vientiane: daytime highs average 29.6°C and nights cool to about 23.8°C. By daytime temperature it is the joint 7th warmest of the 12 months.
Expect about 300 mm of rain on roughly 25 days, which makes September a very wet month (the 9th driest of the 12 months). Daylight, from sunrise to sunset, lasts about 12 h 15 min on an average September day.
The nearest other city in this atlas is Udon Thani (64 km away). In September its highs average 29.9°C, about as warm as Vientiane, with 276 mm of rain.
Among the 4 cities listed in Laos, Vientiane ranks 1st of 4 for the warmest September highs and 2nd of 4 for the driest September (rainfall, lowest first). The mean September high of those 4 cities is 29.3°C; Vientiane is 0.3°C warmer than that mean.
From September to October, average highs fall by 0.3°C to 29.3°C, and monthly rainfall falls from 300 mm to 101 mm.
The annual picture
September in context
Monthly rainfall
Average total · mmAverages from hourly ERA5 reanalysis data. Actual weather varies from year to year. How these numbers are calculated
Every month, side by side
Vientiane climate table
| Month | Average highHigh / low | Average low | Rainfall mm/month | Rain days ≥1 mm/day | Daylight hours/dayDaylight h/day |
|---|---|---|---|---|---|
| January | 27.3°C17.0°C | 17.0°C | 11 | 1.8 | 11.211 h |
| February | 29.8°C18.9°C | 18.9°C | 15 | 2.2 | 11.512 h |
| March | 32.6°C22.1°C | 22.1°C | 36 | 6.2 | 12.012 h |
| April | 33.8°C24.4°C | 24.4°C | 75 | 11.9 | 12.513 h |
| May | 31.9°C24.7°C | 24.7°C | 261 | 23.4 | 13.013 h |
| June | 30.5°C24.7°C | 24.7°C | 316 | 25.0 | 13.213 h |
| July | 29.9°C24.4°C | 24.4°C | 372 | 26.5 | 13.113 h |
| August | 29.6°C24.1°C | 24.1°C | 401 | 27.4 | 12.713 h |
| September, selected | 29.6°C23.8°C | 23.8°C | 300 | 24.7 | 12.312 h |
| October | 29.3°C22.7°C | 22.7°C | 101 | 11.9 | 11.712 h |
| November | 28.7°C20.2°C | 20.2°C | 22 | 3.0 | 11.311 h |
| December | 26.9°C17.3°C | 17.3°C | 8.4 | 1.2 | 11.111 h |
Rainfall is the average of the 30 separate monthly totals. A rain day is a local calendar day with at least 1 mm of precipitation. Daylight is the calculated sunrise-to-sunset length, not measured sunshine.
Compare places
September in nearby cities
- Udon Thani in SeptemberThailand · 64 kmHigh 29.9°C · Low 23.7°C · 276 mm rain
- Khon Kaen in SeptemberThailand · 171 kmHigh 30.1°C · Low 23.8°C · 237 mm rain
- Sakon Nakhon in SeptemberThailand · 187 kmHigh 29.7°C · Low 23.7°C · 268 mm rain
- Thakhèk in SeptemberLaos · 244 kmHigh 29.4°C · Low 23.1°C · 317 mm rain
- Savannakhet in SeptemberLaos · 277 kmHigh 29.4°C · Low 23.3°C · 257 mm rain
- Lampang in SeptemberThailand · 330 kmHigh 29.1°C · Low 23.3°C · 256 mm rain
- Vinh in SeptemberVietnam · 336 kmHigh 29.9°C · Low 25.0°C · 330 mm rain
- Nakhon Ratchasima in SeptemberThailand · 337 kmHigh 30.3°C · Low 23.7°C · 231 mm rain
Read the numbers correctly
Climate, not a promise.
These patterns help compare months. They cannot tell you the weather on a specific day of your trip.
Sources, method and limitsHow these numbers are made (what the highs, lows and rain days mean, the sources and the model cell used for Vientiane) is explained once on the Vientiane year overview and on the Sources, method and limits page.