Cổ Đô weather in September

In September, Cổ Đô sees average daytime highs of 31°C and overnight lows near 25°C, with 230 mm of rain across 18.8 wet days and about 12.1 hours of daylight. It is the 5th-warmest and 4th-wettest month of the year here.

Day-to-day highs hold fairly steady near 31°C through the month. The sky is clear or mostly clear about 21% of the time in September, and the air most often feels miserable.

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 Cổ Đô's 4th-clearest and 8th-windiest month. For the whole year in context, see Cổ Đô's year-round climate.

Daytime high
31°
5th warmest
Overnight low
25°
9th coldest
Rainfall
230 mm
18.8 wet days
Daylight
12 h 06 min
5:49 AM – 5:56 PM
Cloud cover
71%
4th clearest
Wind
5 km/h
8th windiest
Solar energy
4.23 kWh/m²
Travel score
3.5
out of 10

Temperature in September

Average highAverage lowShaded bands: 10–90% of days

Day-to-day highs hold fairly steady near 31°C through the month.

A typical September day in Cổ Đô reaches about 31°C in the afternoon and slips back to 25°C overnight — a 6°C spread between the day's warmth and the night's chill. On most days the high lands between 27°C and 34°C. Set against its neighbours, September runs about 1°C cooler than August and about 2°C warmer than October.

20°25°30°35°151015202530
Avg high (°C)Avg low (°C)
13225
23225
33225
43225
53125
63125
73125
83125
93125
103125
113125
123125
133125
143125
153125
163125
173125
183125
193125
203124
213124
223124
233124
243124
253024
263024
273024
283024
293024
303024

How September really feels in Cổ Đô

Once humidity and wind are folded in, September averages 30 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
30
5 feel dangerously hot (≥ 39°C)
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.

Cổ Đô weather by month

How September compares with the rest of the year at a glance. September is the 5th-warmest and 4th-wettest month here — the current month is highlighted below.

MonthHigh / Low (°C)Rainfall (mm)Wet daysDaylight (hours)Travel score
Jan19° / 14°459.110.86.0
Feb21° / 15°348.511.36.3
Mar24° / 18°6111.611.86.3
Apr29° / 22°10312.212.55.2
May31° / 25°23017.9133.4
Jun33° / 26°23819.113.32.6
Jul33° / 26°29120.913.22.6
Aug32° / 26°35422.512.72.7
Sep31° / 25°23018.812.13.5
Oct29° / 22°11911.611.55.6
Nov25° / 19°587.5117.1
Dec21° / 15°387.610.76.8

Cloud cover in September

ClearMostly clearPartly cloudyMostly cloudyOvercast

The sky is clear or mostly clear about 21% of the time in September.

Beyond those clear spells, partly cloudy skies cover about 13% of September, with mostly cloudy or overcast conditions the remaining 67%. Skies tend to open up as the month goes on.

0%25%50%75%100%151015202530
Clearer (%)Cloudier (%)
12377
22377
32476
42476
52476
62674
72674
82674
92773
102773
112971
123070
133070
143169
153367
163367
173565
183664
193763
203862
213961
223961
234159
244159
254357
264357
274357
284456
294456
304555

Chance of precipitation in September

Any precipitation

Cổ Đô gets around 230 mm of rain over 18.8 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 63% and peaks near 75% on the wettest days. The odds ease toward the end of the month.

0%20%40%60%80%151015202530
Rain chance (%)
175
275
374
474
574
673
772
872
971
1070
1169
1267
1366
1465
1564
1662
1761
1860
1958
2057
2156
2255
2354
2453
2552
2651
2750
2850
2949
3049

Humidity in September

DryComfortableHumidMuggyOppressiveMiserable

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

By dew point, September lands in the miserable band about 67% of days. Sticky, muggy-or-worse air turns up on roughly 99% of them.

0%25%50%75%100%151015202530
Humid (%)Muggy (%)Oppressive (%)Miserable (%)
100991
2001090
3001090
4001189
5011287
6011386
7011485
8011584
9021781
10021880
11021979
12132076
13132274
14142372
15142570
16152767
17152866
18163063
19163261
20173359
21183556
22183754
23193951
242104049
252104246
262114343
272124541
283134639
293144736
303154734

Wind in September

Winds average 5 km/h in September.

Across September, daily wind ranges from about 5 km/h on the calmest days to 5 km/h at its breeziest. It stays fairly steady from day to day.

0246810151015202530
Wind speed (km/h)Feels
15calm
25calm
35calm
45calm
55calm
65calm
75calm
85calm
95calm
105calm
115calm
125calm
135calm
145calm
155calm
165calm
175calm
185calm
195calm
205calm
215calm
225calm
235calm
245calm
255calm
265calm
275calm
285calm
295calm
305calm

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 5:45 AM to 5:53 AM, and sunset from 6:11 PM to 5:43 PM.

12 AM4 AM8 AM12 PM4 PM8 PM12 AM151015202530
Daylight (h)Sunrise (AM)Sunset (PM)
112.45:456:11
212.45:466:10
312.45:466:09
412.45:466:08
512.35:466:07
612.35:476:06
712.35:476:05
812.35:476:04
912.35:476:03
1012.25:486:02
1112.25:486:01
1212.25:486:00
1312.25:485:59
1412.25:495:58
1512.15:495:57
1612.15:495:56
1712.15:505:55
1812.15:505:54
1912.15:505:53
2012.05:505:52
2112.05:515:51
2212.05:515:50
2312.05:515:50
2412.05:515:49
2511.95:525:48
2611.95:525:47
2711.95:525:46
2811.95:525:45
2911.85:535:44
3011.85:535:43

Solar energy in September

Daily solar energy (kWh/m²)

Average shortwave solar energy reaching the ground each day in September, about 4.23 kWh/m².

For context, solar energy here swings from a low near 2.16 kWh/m² to a high of 4.77 kWh/m² in June across the year — September's 4.23 kWh/m² falls in the middle.

012345151015202530
Solar energy (kWh/m²)Level
14.3Bright
24.3Bright
34.3Bright
44.3Bright
54.3Bright
64.3Bright
74.2Bright
84.2Bright
94.2Bright
104.2Bright
114.2Bright
124.2Bright
134.2Bright
144.2Bright
154.2Bright
164.2Bright
174.2Bright
184.2Bright
194.2Bright
204.2Bright
214.2Bright
224.2Bright
234.2Bright
244.2Bright
254.2Bright
264.2Bright
274.2Bright
284.2Bright
294.2Bright
304.2Bright
Planning a trip in September

Hazard calendar for Cổ Đô

In seasonPeak

In September, Cổ Đô sits inside its pacific typhoon and monsoon season. The full year is below, with each hazard's peak months called out.

Cổ Đô sits in the Pacific typhoon belt; the season peaks July–October.

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

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

Is September a good time to visit Cổ Đô?

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

3.5
Sightseeing
8th-best month of the year
5.2
Beach & pool
6th-best month of the year

September is a weaker month for outdoor sightseeing in Cổ Đô.

What to pack for Cổ Đô in September

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

In September, Cổ Đô sees daytime highs around 31°C and nights near 25°C. Pack light clothes and rain gear. About 19 days see rain.

light clothesrain gear

UV index in Cổ Đô in September

LowModerateHighVery highExtreme

Clear-sky midday UV in September peaks around 6 — enough to warrant sun protection. The full-year curve, shaded by WHO exposure level, is below.

Under clear skies, the midday UV index in Cổ Đô peaks around June 20 at about 12 (extreme) — sunscreen, a hat and midday shade are essential. It bottoms out near November 20 at about 5 (high).

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

025710JanFebMarAprMayJunJulAugSepOctNovDecHighVery highHighVery highExtremeHighJun 20UV 12Nov 20UV 5
UV index (midday)Level
Jan6High
Feb7High
Mar8Very high
Apr6High
May8Very high
Jun12Extreme
Jul11Extreme
Aug11Extreme
Sep6High
Oct7Very high
Nov5High
Dec6High

Air quality in Cổ Đô 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 Cổ Đô is worst in April — around 98 µg/m³ PM2.5 (unhealthy), about 3.8× the cleanest month (July, 26 µg/m³).

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

0306090120JanFebMarAprMayJunJulAugSepOctNovDecUnhealthyPoorModeratePoorUnhealthyApr 1494 µg/m³Jul 2026 µg/m³
PM2.5 (µg/m³)Level
Jan76Unhealthy
Feb71Unhealthy
Mar76Unhealthy
Apr98Unhealthy
May57Unhealthy
Jun32Moderate
Jul26Moderate
Aug28Moderate
Sep39Poor
Oct53Poor
Nov66Unhealthy
Dec77Unhealthy
Location & terrain

Where is Cổ Đô?

Cổ Đô sits at 21.3°N, 105.4°E, 17 m above sea level, in Vietnam. The nearest listed city is Việt Trì, 6.0 km away.

Topography around Cổ Đô

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

Within 3 km, the terrain around Cổ Đô has only modest variations in elevation — a maximum elevation change of 22 m around an average of 13 m above sea level; within 16 km, significant variations in elevation — a maximum elevation change of 333 m; within 80 km, very significant variations in elevation — a maximum elevation change of 2,211 m.

The land around Cổ Đô is covered by cropland (39%) within 3 km, trees (42%) and cropland (33%) within 16 km, and trees (72%) within 80 km.

3 km
22 m
16 km
333 m
80 km
2,211 m
treesgrasslandcroplandartificial surfacesbare terrainwater
September weather nearby: Việt Trì 6.0 km · Phú Thọ 20 km · Sơn Tây 21 km · Ba Vì 22 km · Vĩnh Yên 25 km · Phúc Yên 36 km · Đan Phượng 37 km · Thượng Cát 43 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 Cổ Đô (21.2796°, 105.364°, elevation 17 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. Tropical-cyclone seasons are the published climatological basin seasons (NOAA National Hurricane Center / regional warning centres). 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).