Sơn La weather in September

In September, Sơn La sees average daytime highs of 29°C and overnight lows near 21°C, with 150 mm of rain across 17.5 wet days and about 12.1 hours of daylight. It is the 6th-warmest and 4th-wettest month of the year here.

Day-to-day highs hold fairly steady near 29°C through the month. The sky is clear or mostly clear about 16% of the time in September, and the air most often feels oppressive.

Daylight stretches from about 12 h 24 min at the start of September to 11 h 48 min by month's end. Set against the rest of the year, September is Sơn La's 9th-clearest and 11th-windiest month. For the whole year in context, see Sơn La's year-round climate.

Daytime high
29°
6th warmest
Overnight low
21°
8th coldest
Rainfall
150 mm
17.5 wet days
Daylight
12 h 06 min
5:55 AM – 6:02 PM
Cloud cover
73%
9th clearest
Wind
4 km/h
11th windiest
Solar energy
4.36 kWh/m²
Travel score
4.4
out of 10

Sơn La is the old provincial capital of Son La province, Vietnam.

Density
328/km²
people per km²

Air quality: WHO Ambient Air Quality Database. Density & description: Wikidata (CC0), GeoNames.

Temperature in September

Average highAverage lowShaded bands: 10–90% of days

Day-to-day highs hold fairly steady near 29°C through the month.

A typical September day in Sơn La reaches about 29°C in the afternoon and slips back to 21°C overnight — a 7°C spread between the day's warmth and the night's chill. On most days the high lands between 26°C and 31°C. Set against its neighbours, September runs on par with August and about 2°C warmer than October.

15°20°25°30°35°151015202530
Avg high (°C)Avg low (°C)
12922
22922
32922
42922
52922
62922
72922
82922
92922
102922
112922
122922
132922
142922
152922
162921
172921
182921
192921
202921
212921
222921
232921
242921
252921
262821
272821
282821
292821
302821

How September really feels in Sơn La

Once humidity and wind are folded in, September averages 5 days that feel above 32°C and 0 that feel at or below 0°C — the comfort signal a plain temperature reading hides.

Days feeling ≥ 32°C
5
heat index over the day's high
Days feeling ≤ C
0
wind chill below the day's low

The story in September is heat — humidity pushes the afternoon "feels like" well above the raw temperature.

Sơn La weather by month

How September compares with the rest of the year at a glance. September is the 6th-warmest and 4th-wettest month here — the current month is highlighted below.

MonthHigh / Low (°C)Rainfall (mm)Wet daysDaylight (hours)Travel score
Jan21° / 12°24410.87.3
Feb23° / 13°193.611.37.9
Mar27° / 16°507.111.87.1
Apr29° / 19°7212.812.55.2
May30° / 22°14719.3133.7
Jun30° / 23°2092313.33.2
Jul29° / 23°28824.513.23.4
Aug29° / 22°28325.312.73.4
Sep29° / 21°15017.512.14.4
Oct27° / 19°498.311.56.6
Nov25° / 16°274.5117.8
Dec22° / 12°233.610.77.6

Cloud cover in September

ClearMostly clearPartly cloudyMostly cloudyOvercast

The sky is clear or mostly clear about 16% of the time in September.

Beyond those clear spells, partly cloudy skies cover about 15% of September, with mostly cloudy or overcast conditions the remaining 69%. Skies tend to open up as the month goes on.

0%25%50%75%100%151015202530
Clearer (%)Cloudier (%)
12377
22377
32377
42377
52377
62377
72575
82575
92575
102575
112674
122674
132872
142773
152872
162971
172971
183268
193268
203367
213565
223664
233862
243961
254060
264159
274258
284357
294555
304555

Chance of precipitation in September

Any precipitation

Sơn La gets around 150 mm of rain over 17.5 wet days in September. The line is the day-by-day chance of measurable precipitation.

Day to day, the chance of measurable rain averages around 59% and peaks near 73% on the wettest days. The odds ease toward the end of the month.

0%20%40%60%80%151015202530
Rain chance (%)
173
273
372
471
570
669
768
867
966
1065
1165
1264
1363
1462
1561
1660
1758
1857
1956
2055
2153
2252
2350
2449
2547
2645
2744
2843
2942
3040

Humidity in September

DryComfortableHumidMuggyOppressiveMiserable

Most of September feels oppressive — the stacked bands show each day's mix of comfort levels, read off the dew point.

By dew point, September lands in the oppressive band about 63% of days. Sticky, muggy-or-worse air turns up on roughly 94% of them.

0%25%50%75%100%151015202530
Comfortable (%)Humid (%)Muggy (%)Oppressive (%)
1001189
2011287
3011386
4011584
5011683
6011881
7021979
8022078
9022276
10022375
11122473
12132670
13132769
14132868
15143065
16143164
17153262
18153460
19163558
20163657
21173854
22183952
23184149
24194247
252104445
262114543
272124640
282134738
292144837
302154835

Wind in September

Winds average 4 km/h in September.

Across September, daily wind ranges from about 4 km/h on the calmest days to 4 km/h at its breeziest. It stays fairly steady from day to day.

0246810151015202530
Wind speed (km/h)Feels
14calm
24calm
34calm
44calm
54calm
64calm
74calm
84calm
94calm
104calm
114calm
124calm
134calm
144calm
154calm
164calm
174calm
184calm
194calm
204calm
214calm
224calm
234calm
244calm
254calm
264calm
274calm
284calm
294calm
304calm

Sunrise & sunset in September

DaylightNight

Daylight runs from about 12 h 24 min at the start of September to 11 h 48 min by month's end. The lit band spans sunrise to sunset each day.

Days shrink by about 36 minutes over September. Sunrise moves from 5:51 AM to 5:59 AM, and sunset from 6:17 PM to 5:48 PM.

12 AM4 AM8 AM12 PM4 PM8 PM12 AM151015202530
Daylight (h)Sunrise (AM)Sunset (PM)
112.45:516:17
212.45:516:16
312.45:526:15
412.45:526:14
512.35:526:13
612.35:526:12
712.35:536:11
812.35:536:10
912.35:536:09
1012.25:546:08
1112.25:546:07
1212.25:546:06
1312.25:546:05
1412.25:556:04
1512.15:556:03
1612.15:556:02
1712.15:556:01
1812.15:566:00
1912.15:565:59
2012.05:565:58
2112.05:565:57
2212.05:575:56
2312.05:575:55
2412.05:575:54
2511.95:575:53
2611.95:585:52
2711.95:585:51
2811.95:585:50
2911.85:595:49
3011.85:595:48

Solar energy in September

Daily solar energy (kWh/m²)

Average shortwave solar energy reaching the ground each day in September, about 4.36 kWh/m².

For context, solar energy here swings from a low near 3.14 kWh/m² to a high of 5.26 kWh/m² in April across the year — September's 4.36 kWh/m² falls in the middle.

012345151015202530
Solar energy (kWh/m²)Level
14.4Bright
24.4Bright
34.4Bright
44.4Bright
54.4Bright
64.4Bright
74.4Bright
84.4Bright
94.4Bright
104.4Bright
114.3Bright
124.3Bright
134.3Bright
144.3Bright
154.3Bright
164.3Bright
174.3Bright
184.3Bright
194.3Bright
204.3Bright
214.3Bright
224.3Bright
234.3Bright
244.3Bright
254.3Bright
264.3Bright
274.3Bright
284.3Bright
294.3Bright
304.3Bright
Planning a trip in September

Hazard calendar for Sơn La

In seasonPeak

In September, Sơn La sits inside its monsoon season. The full year is below, with each hazard's peak months called out.

Sơn La's monsoon runs May–September, when most of the year's rain falls.

Monsoon
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec

Is September a good time to visit Sơn La?

Our two travel scores rate September for general sightseeing and for beach or pool weather — 0 (poor) to 10 (ideal).

4.4
Sightseeing
8th-best month of the year
5.6
Beach & pool
6th-best month of the year

September is a reasonable time to visit Sơn La for sightseeing.

What to pack for Sơn La in September

From September's temperature range, rain chance, sun and wind — what's worth putting in the bag.

In September, Sơn La sees daytime highs around 29°C and nights near 21°C. Pack light clothes and rain gear. About 18 days see rain.

light clothesrain gear

UV index in Sơn La in September

LowModerateHighVery highExtreme

Clear-sky midday UV in September peaks around 9 (very high — sun protection essential). The full-year curve, shaded by WHO exposure level, is below.

Under clear skies, the midday UV index in Sơn La peaks around June 20 at about 13 (extreme) — sunscreen, a hat and midday shade are essential. It bottoms out near December 18 at about 6 (high).

The index reaches 3 or more — the level where the WHO recommends sun protection — every month of the year.

025710JanFebMarAprMayJunJulAugSepOctNovDecVery highExtremeVery highExtremeVery highHighJun 20UV 13Dec 18UV 6
UV index (midday)Level
Jan7Very high
Feb9Very high
Mar11Extreme
Apr9Very high
May11Extreme
Jun14Extreme
Jul13Extreme
Aug13Extreme
Sep9Very high
Oct9Very high
Nov8Very high
Dec6High

Air quality in Sơn La in September

GoodModeratePoorUnhealthyVery unhealthy

Average fine-particle pollution (PM2.5) through the year — so you can see where September falls, not just the annual average.

Air quality in Sơn La is worst in April — around 151 µg/m³ PM2.5 (very unhealthy), about 12.9× the cleanest month (August, 12 µg/m³).

Modeled monthly averages (CAMS reanalysis, 2015–2024).

0306090120150JanFebMarAprMayJunJulAugSepOctNovDecModeratePoorUnhealthyModerateGoodModerateApr 16140 µg/m³Aug 912 µg/m³
PM2.5 (µg/m³)Level
Jan32Moderate
Feb38Poor
Mar67Unhealthy
Apr151Very unhealthy
May58Unhealthy
Jun14Moderate
Jul12Good
Aug12Good
Sep16Moderate
Oct23Moderate
Nov26Moderate
Dec31Moderate
Location & terrain

Where is Sơn La?

Sơn La sits at 21.3°N, 103.9°E, 608 m above sea level, in Vietnam. The nearest listed city is Ít Ong, 24 km away.

Dien Bien PhuXam NuaVieng XaiMường LayYên Bái

Topography around Sơn La

How much the land rises and falls, and what covers it, within 3, 16 and 80 km of Sơn La.

Within 3 km, the terrain around Sơn La has significant variations in elevation — a maximum elevation change of 348 m around an average of 674 m above sea level; within 16 km, very significant variations in elevation — a maximum elevation change of 1,404 m; within 80 km, extreme variations in elevation — a maximum elevation change of 2,830 m.

The land around Sơn La is covered by trees (59%) within 3 km, trees (69%) and grassland (21%) within 16 km, and trees (68%) and grassland (27%) within 80 km.

3 km
348 m
16 km
1,404 m
80 km
2,830 m
treesgrasslandcroplandartificial surfacesbare terrainwater
September weather nearby: Ít Ong 24 km · Thị Trấn Thuận Châu 27 km · Nghĩa Lộ 69 km · Dien Bien Phu 93 km · Xam Nua 102 km · Vieng Xai 107 km · Mường Lay 111 km · Yên Bái 112 km

Vietnam travel facts

Travel advisory
Level 1
Exercise Normal Precautions
Power plugs
Type A / B / C / F
220 V · 50 Hz
Prices
≈ 29% of US
price level, 2025
GDP per capita
$5,066
2025
Happiness
6.4 / 10
World Happiness, 2025
Safe drinking water
59%
of population, 2024
Homicide rate
1.5
per 100k, 2011
Road deaths
30.6
per 100k/yr, 2019
Income group
Upper middle
World Bank
English
Moderate
EF EPI 500
Religion
none 86%Catholic 6%Buddhist 6%Protestant 1%

Sources: World Bank, US State Department, World Happiness Report, WHO/UNICEF, EF EPI, CIA World Factbook.

Data sources

Temperature, precipitation, cloud, humidity, wind and solar figures are a 1991–2020 climatology for Sơn La (21.3256°, 103.9188°, elevation 608 m), computed from hourly ERA5 reanalysis — contains modified Copernicus Climate Change Service information. Sun figures are astronomical calculations, not observations. City data © GeoNames, CC BY 4.0. Map outlines from Natural Earth (public domain); interactive map © Google. UV index is derived from CAMS (Copernicus Atmosphere Monitoring Service) clear-sky UV data — contains modified Copernicus Atmosphere Monitoring Service information. Monthly air-quality (PM2.5) seasonality is from the CAMS EAC4 reanalysis (Copernicus Atmosphere Monitoring Service), scaled to the WHO annual mean where available. Topography is sampled from the Copernicus DEM GLO-90 elevation model (© ESA/Airbus) and ESA WorldCover 2021 land cover (CC BY 4.0).