Rio Branco weather in September

In September, Rio Branco sees average daytime highs of 33°C and overnight lows near 22°C, with 76 mm of rain across 11.9 wet days and about 11.9 hours of daylight. It is the 1st-warmest and 9th-wettest month of the year here.

Day-to-day highs hold fairly steady near 33°C through the month. The sky is clear or mostly clear about 29% of the time in September, and the air most often feels oppressive.

Daylight stretches from about 11 h 48 min at the start of September to 12 h 06 min by month's end. Set against the rest of the year, September is Rio Branco's 4th-clearest and 2nd-windiest month. For the whole year in context, see Rio Branco's year-round climate.

Daytime high
33°
1st warmest
Overnight low
22°
5th coldest
Rainfall
76 mm
11.9 wet days
Daylight
11 h 54 min
5:27 AM – 5:24 PM
Cloud cover
59%
4th clearest
Wind
6 km/h
2nd windiest
Solar energy
5.57 kWh/m²
Travel score
3.2
out of 10

Rio Branco is human settlement in Acre, Brazil.

Founded
1882

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 33°C through the month.

A typical September day in Rio Branco reaches about 33°C in the afternoon and slips back to 22°C overnight — a 11°C spread between the day's warmth and the night's chill. On most days the high lands between 30°C and 36°C. Set against its neighbours, September runs on par with August and about 1°C warmer than October.

15°20°25°30°35°40°151015202530
Avg high (°C)Avg low (°C)
13322
23322
33322
43322
53322
63322
73322
83322
93322
103322
113322
123322
133322
143322
153322
163322
173322
183322
193322
203322
213322
223322
233322
243322
253322
263322
273322
283322
293322
303322

How September really feels in Rio Branco

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
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.

Rio Branco weather by month

How September compares with the rest of the year at a glance. September is the 1st-warmest and 9th-wettest month here — the current month is highlighted below.

MonthHigh / Low (°C)Rainfall (mm)Wet daysDaylight (hours)Travel score
Jan30° / 23°25527.712.52.8
Feb30° / 23°2402512.32.8
Mar30° / 23°24927.212.12.8
Apr30° / 22°16022.811.83.2
May30° / 21°7615.411.54.3
Jun30° / 20°306.811.45.3
Jul31° / 20°214.211.55.1
Aug33° / 20°386.311.74.0
Sep33° / 22°7611.911.93.2
Oct33° / 23°13719.512.22.8
Nov31° / 23°19922.912.52.8
Dec30° / 23°24626.312.62.9

Cloud cover in September

ClearMostly clearPartly cloudyMostly cloudyOvercast

The sky is clear or mostly clear about 29% of the time in September.

Beyond those clear spells, partly cloudy skies cover about 24% of September, with mostly cloudy or overcast conditions the remaining 47%. Skies tend to cloud over as the month goes on.

0%25%50%75%100%151015202530
Clearer (%)Cloudier (%)
16733
26634
36535
46535
56337
66337
76238
86040
96040
105842
115743
125743
135644
145446
155347
165248
175149
185050
194951
204852
214753
224654
234555
244456
254357
264258
274258
284159
294060
303961

Chance of precipitation in September

Any precipitation

Rio Branco gets around 76 mm of rain over 11.9 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 40% and peaks near 50% on the wettest days. The odds climb toward the end of the month.

0%20%40%60%151015202530
Rain chance (%)
129
229
330
430
531
631
732
833
933
1034
1135
1236
1337
1438
1539
1641
1742
1843
1944
2044
2145
2246
2346
2447
2548
2648
2749
2849
2950
3050

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 75% of days. Sticky, muggy-or-worse air turns up on roughly 91% of them.

0%25%50%75%100%151015202530
Dry (%)Comfortable (%)Humid (%)Muggy (%)Oppressive (%)Miserable (%)
134818670
234818670
324817681
424817681
524816691
623716711
723716711
823716711
923716711
1023616721
1113616731
1213616722
1313515742
1413515742
1513515742
1613414762
1713414762
1813414762
1913413772
2013313773
2103313783
2203313783
2302312803
2402312803
2502312803
2602211823
2702211814
2802210824
2902210824
3002210815

Wind in September

Winds average 6 km/h in September.

Across September, daily wind ranges from about 6 km/h on the calmest days to 6 km/h at its breeziest. It stays fairly steady from day to day.

0246810151015202530
Wind speed (km/h)Feels
16calm
26calm
36calm
46calm
56calm
66calm
76calm
86calm
96calm
106calm
116calm
126calm
136calm
146calm
156calm
166calm
176calm
186calm
196calm
206calm
216calm
226calm
236calm
246calm
256calm
266calm
276calm
286calm
296calm
306calm

Sunrise & sunset in September

DaylightNight

Daylight runs from about 11 h 48 min at the start of September to 12 h 06 min by month's end. The lit band spans sunrise to sunset each day.

Days grow by about 18 minutes over September. Sunrise moves from 5:37 AM to 5:18 AM, and sunset from 5:25 PM to 5:23 PM.

12 AM4 AM8 AM12 PM4 PM8 PM12 AM151015202530
Daylight (h)Sunrise (AM)Sunset (PM)
111.85:375:25
211.85:365:25
311.85:365:25
411.85:355:25
511.85:345:25
611.95:345:25
711.95:335:25
811.95:325:25
911.95:325:25
1011.95:315:24
1111.95:305:24
1211.95:305:24
1311.95:295:24
1411.95:295:24
1511.95:285:24
1611.95:275:24
1712.05:275:24
1812.05:265:24
1912.05:255:24
2012.05:255:24
2112.05:245:23
2212.05:235:23
2312.05:235:23
2412.05:225:23
2512.05:215:23
2612.05:215:23
2712.05:205:23
2812.15:195:23
2912.15:195:23
3012.15:185:23

Solar energy in September

Daily solar energy (kWh/m²)

Average shortwave solar energy reaching the ground each day in September, about 5.57 kWh/m² — the sunniest month for solar.

For context, solar energy here swings from a low near 4.25 kWh/m² to a high of 5.57 kWh/m² in September across the year — September's 5.57 kWh/m² sits near the top of that range.

0246151015202530
Solar energy (kWh/m²)Level
15.5Bright
25.5Bright
35.5Bright
45.5Bright
55.5Bright
65.5Bright
75.5Bright
85.5Bright
95.5Bright
105.5Bright
115.5Bright
125.6Bright
135.6Bright
145.6Bright
155.6Bright
165.6Bright
175.6Bright
185.6Bright
195.6Bright
205.6Bright
215.6Bright
225.6Bright
235.6Bright
245.6Bright
255.6Bright
265.6Bright
275.6Bright
285.6Bright
295.6Bright
305.6Bright
Planning a trip in September

Hazard calendar for Rio Branco

In seasonPeak

None of Rio Branco's seasonal hazards are active in September. The full-year calendar below shows when the rainy season, cyclone risk and dust haze do peak.

Rio Branco's rainy season runs October–April, when most of the year's rain falls.

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

Is September a good time to visit Rio Branco?

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

3.2
Sightseeing
5th-best month of the year
5.8
Beach & pool
5th-best month of the year

September is a weaker month for outdoor sightseeing in Rio Branco.

What to pack for Rio Branco in September

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

In September, Rio Branco sees daytime highs around 33°C and nights near 22°C. Pack light clothes. Worth having: rain gear and sun protection. About 12 days see rain.

light clothesrain gearsun protection

UV index in Rio Branco in September

LowModerateHighVery highExtreme

Clear-sky midday UV in September peaks around 4 — enough to warrant sun protection. The full-year curve, shaded by WHO exposure level, is below.

Under clear skies, the midday UV index in Rio Branco peaks around January 20 at about 15 (extreme) — sunscreen, a hat and midday shade are essential. It bottoms out near September 12 at about 5 (moderate).

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

025710JanFebMarAprMayJunJulAugSepOctNovDecExtremeVery highHighExtremeJan 20UV 15Sep 12UV 5
UV index (midday)Level
Jan15Extreme
Feb15Extreme
Mar14Extreme
Apr13Extreme
May11Extreme
Jun9Very high
Jul8Very high
Aug7High
Sep4Moderate
Oct12Extreme
Nov13Extreme
Dec13Extreme

Air quality in Rio Branco 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 Rio Branco is worst in September — around 100 µg/m³ PM2.5 (unhealthy), about 12.4× the cleanest month (June, 8 µg/m³).

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

0306090120JanFebMarAprMayJunJulAugSepOctNovDecModerateGoodModerateUnhealthyModerateGoodSep 1394 µg/m³Jun 98 µg/m³
PM2.5 (µg/m³)Level
Jan13Moderate
Feb13Moderate
Mar13Moderate
Apr10Good
May8Good
Jun8Good
Jul14Moderate
Aug65Unhealthy
Sep100Unhealthy
Oct27Moderate
Nov13Moderate
Dec11Good
Location & terrain

Where is Rio Branco?

Rio Branco sits at 10.0°S, 67.8°W, 153 m above sea level, in Brazil. The nearest listed city is Senador Guiomard, 21 km away.

Topography around Rio Branco

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

Within 3 km, the terrain around Rio Branco has only modest variations in elevation — a maximum elevation change of 50 m around an average of 142 m above sea level; within 16 km, only modest variations in elevation — a maximum elevation change of 103 m; within 80 km, only modest variations in elevation — a maximum elevation change of 165 m.

The land around Rio Branco is covered by artificial surfaces (54%) and trees (33%) within 3 km, trees (46%) and grassland (46%) within 16 km, and trees (61%) and grassland (38%) within 80 km.

3 km
50 m
16 km
103 m
80 km
165 m
treesgrasslandartificial surfaceswater
September weather nearby: Senador Guiomard 21 km · Porto Acre 53 km · Plácido de Castro 79 km · Xapuri 107 km · Sena Madureira 139 km · Boca do Acre 143 km · Brasiléia 155 km · Epitaciolândia 155 km

Brazil travel facts

Travel advisory
Level 2
Exercise Increased Caution
Power plugs
Type C / N
127 / 220 V · 60 Hz
Prices
≈ 46% of US
price level, 2025
GDP per capita
$10,713
2025
Happiness
6.6 / 10
World Happiness, 2025
Safe drinking water
89%
of population, 2024
Homicide rate
19.3
per 100k, 2023
Road deaths
16
per 100k/yr, 2019
Income group
Upper middle
World Bank
English
Low
EF EPI 482
Religion
Roman Catholic 57%Evangelical 27%none 9%other 4%

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 Rio Branco (-9.9747°, -67.81°, elevation 153 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).