Alter do Chão weather in September
September in Alter do Chão: sweltering, a little rain, with clean air — fine if you can take 38°C afternoons.
Updated September 2026 · climate normals from ERA5 reanalysis
#2 of 12 months in Alter do Chão · #355 of 1413 destinations to visit in September · comfort 87/100 (tier A)
- Days
- 33°C
- Nights
- 26°C
- Wet days
- 7
- Sun
- 10.8 h
- Humidity
- 71%
- Daylight
- 12 h
Traveller notes on Alter do Chão in September
Forum posters describe September as squarely inside the Amazon's dry season - locally called 'summer,' running roughly July to December - which is also when Alter do Chao's famous river-sand beaches along the Tapajos emerge as water levels drop. Visitor reports from within this dry stretch describe delightful, warm conditions and calm, low water levels ideal for beach time and swimming, in contrast to the wetter 'winter' months when the river rises and submerges the beaches entirely. Posters treat the dry season generally, and September specifically, as the reliable window to actually see and enjoy the riverside beaches this destination is known for, rather than a hit-or-miss gamble on water levels.
Other months in Alter do Chão
Amazon-region forum threads describe January as squarely within what locals call the Amazonian 'winter' - the wet season - with genuinely heavy rain possible, though posters were consistent that it's very unusual for rain to fall the entire day; sun typically breaks through at some point. That said, one thread specifically warned that during the peak of the rainy season the surrounding area can flood, and recommended the dry season (roughly July through December, aligned with the Southern Hemisphere's drier months) instead for anyone prioritizing accessible trails and beaches over the lush, high-water river scenery January brings.
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Alter do Chão climate normals — September
Monthly averages from ERA5 reanalysis. AQI is the mean US Air Quality Index for the month.
Crowds in Alter do Chão in September
How busy the place itself is — school and mass holidays, the months an editor tagged, and how sought-after the weather makes them. Never part of the comfort score.
Peak crowdsRiver beaches emerge, Festival do Sairé, school holidays in 2 of the markets that fill it(estimated)
Peak crowdsBusyShoulder seasonQuiet
Best months for Alter do Chão's weather
Ranked by this destination's own climate comfort score across the year — a different thing from how busy it gets (see Crowds above).
Best weatherAlter do Chão's weather peaks July–September, best around August.
September includes Festival do Sairé.
Best weatherFair weatherToughest weather
What's on in Alter do Chão in September
Recurring seasonal events, natural spectacles, closures and holidays — curated and sourced.
- Season
River beaches emerge
1 Aug – 31 Jan · usuallyHigh waterCrowdedThe Tapajós drops from August and the white sandbanks in front of the village come back out of the water. By September you can wade to the Ilha do Amor, and in a hard year walk to it.
- Festival
Festival do Sairé
17–21 SepMajor festivalCrowdedBook earlyFive days of mast-raising, church procession and the Botos contest, where two dolphin teams sing and dance at each other in a purpose-built arena. Santarém has now fixed it to the third week of September. Source ↗
Where is Alter do Chão?
Alter do Chão in September — FAQ
- Is September a good time to visit Alter do Chão?
- September in Alter do Chão: sweltering, a little rain, with clean air — fine if you can take 38°C afternoons. It ranks #2 of 12 months for Alter do Chão on SeasonMap's comfort score (87/100).
- What is the weather like in Alter do Chão in September?
- In September, Alter do Chão averages a daily high of 32.5°C and a low of 26.1°C, with about 48.4 mm of rain over roughly 7.4 rainy days.
- What is the air quality in Alter do Chão in September?
- Alter do Chão has a mean US Air Quality Index of about 43 in September.