São Luís weather in September

In September, São Luís sees average daytime highs of 29°C and overnight lows near 26°C, with 11 mm of rain across 3.2 wet days and about 12 hours of daylight. It is the 2nd-warmest and 12th-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 80% of the time in September, and the air most often feels oppressive.

Daylight stretches from about 12 hours at the start of September to 12 hours by month's end. Set against the rest of the year, September is São Luís's 1st-clearest and 2nd-windiest month. For the whole year in context, see São Luís's year-round climate.

Daytime high
29°
2nd warmest
Overnight low
26°
11th coldest
Rainfall
11 mm
3.2 wet days
Daylight
12 hours
5:52 AM – 5:51 PM
Cloud cover
31%
1st clearest
Wind
22 km/h
2nd windiest
Solar energy
6.27 kWh/m²
Travel score
7.0
out of 10

São Luís is human settlement in Brazil.

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 São Luís reaches about 29°C in the afternoon and slips back to 26°C overnight — a 2°C spread between the day's warmth and the night's chill. On most days the high lands between 28°C and 29°C. Set against its neighbours, September runs on par with August and on par with October.

24°26°28°30°32°151015202530
Avg high (°C)Avg low (°C)
12926
22926
32926
42926
52926
62926
72926
82926
92926
102926
112926
122926
132926
142926
152926
162926
172926
182926
192926
202926
212926
222926
232926
242926
252826
262826
272826
282826
292826
302826

How September really feels in São Luís

Once humidity and wind are folded in, September averages 0 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
0
heat index over the day's high
Days feeling ≤ C
0
wind chill below the day's low

September sits comfortably in between — no days that feel dangerously hot or drop to a hard freeze once humidity and wind are folded in.

São Luís weather by month

How September compares with the rest of the year at a glance. September is the 2nd-warmest and 12th-wettest month here — the current month is highlighted below.

MonthHigh / Low (°C)Rainfall (mm)Wet daysDaylight (hours)Travel score
Jan28° / 25°22125.412.14.0
Feb28° / 25°3032612.13.6
Mar27° / 25°44030.3123.4
Apr28° / 25°41428.811.93.4
May28° / 26°28626.911.93.7
Jun28° / 26°1532311.94.2
Jul29° / 26°1032011.94.7
Aug29° / 26°28911.96.1
Sep29° / 26°113.2127.0
Oct28° / 26°133.612.16.9
Nov29° / 26°276.812.16.3
Dec28° / 26°7315.312.15.2

Cloud cover in September

ClearMostly clearPartly cloudyMostly cloudyOvercast

The sky is clear or mostly clear about 80% of the time in September, the clearest month of the year.

Beyond those clear spells, partly cloudy skies cover about 13% of September, with mostly cloudy or overcast conditions the remaining 6%. Skies tend to cloud over as the month goes on.

0%25%50%75%100%151015202530
Clearer (%)Cloudier (%)
1964
2964
3964
4964
5964
6964
7964
8964
9964
10964
11946
12946
13946
14946
15946
16946
17937
18928
19928
20928
21928
22928
23928
24928
25928
26928
27919
28919
29919
30919

Chance of precipitation in September

Any precipitation

São Luís gets around 11 mm of rain over 3.2 wet days in September, the driest month. The line is the day-by-day chance of measurable precipitation.

Day to day, the chance of measurable rain averages around 11% and peaks near 16% on the wettest days.

0%10%20%30%151015202530
Rain chance (%)
116
215
315
414
513
613
712
812
911
1011
1111
1211
1311
1411
1511
1611
1711
1811
1910
2010
2110
2210
2310
2410
2510
2610
2710
2810
299
309

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 99% of days. Sticky, muggy-or-worse air turns up on roughly 100% of them.

0%25%50%75%100%151015202530
Oppressive (%)Miserable (%)
1991
21000
31000
4991
5991
6991
7991
8991
9991
10991
11991
12991
13991
14991
15991
16991
17991
18991
19991
20991
21991
22991
23991
24991
25991
26991
27991
28991
29991
30991

Wind in September

Winds average 22 km/h in September.

Across September, daily wind ranges from about 21 km/h on the calmest days to 23 km/h at its breeziest. It stays fairly steady from day to day.

0510152025151015202530
Wind speed (km/h)Feels
121breezy
221breezy
322breezy
422breezy
522breezy
622breezy
722breezy
822breezy
922breezy
1022breezy
1122breezy
1222breezy
1322breezy
1422breezy
1522breezy
1623breezy
1723breezy
1823breezy
1923breezy
2023breezy
2123breezy
2223breezy
2323breezy
2423breezy
2523breezy
2623breezy
2723breezy
2823breezy
2923breezy
3023breezy

Sunrise & sunset in September

DaylightNight

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

Days grow by about 0 minutes over September. Sunrise moves from 5:58 AM to 5:46 AM, and sunset from 5:55 PM to 5:47 PM.

12 AM4 AM8 AM12 PM4 PM8 PM12 AM151015202530
Daylight (h)Sunrise (AM)Sunset (PM)
112.05:585:55
212.05:585:55
312.05:585:55
412.05:575:55
512.05:575:54
612.05:565:54
712.05:565:54
812.05:555:54
912.05:555:53
1012.05:555:53
1112.05:545:53
1212.05:545:52
1312.05:535:52
1412.05:535:52
1512.05:525:51
1612.05:525:51
1712.05:515:51
1812.05:515:51
1912.05:515:50
2012.05:505:50
2112.05:505:50
2212.05:495:49
2312.05:495:49
2412.05:485:49
2512.05:485:48
2612.05:485:48
2712.05:475:48
2812.05:475:48
2912.05:465:47
3012.05:465:47

Solar energy in September

Daily solar energy (kWh/m²)

Average shortwave solar energy reaching the ground each day in September, about 6.27 kWh/m².

For context, solar energy here swings from a low near 4.57 kWh/m² to a high of 6.4 kWh/m² in October across the year — September's 6.27 kWh/m² sits near the top of that range.

0246151015202530
Solar energy (kWh/m²)Level
16.1Intense
26.1Intense
36.1Intense
46.1Intense
56.2Intense
66.2Intense
76.2Intense
86.2Intense
96.2Intense
106.2Intense
116.2Intense
126.2Intense
136.3Intense
146.3Intense
156.3Intense
166.3Intense
176.3Intense
186.3Intense
196.3Intense
206.3Intense
216.3Intense
226.3Intense
236.3Intense
246.3Intense
256.3Intense
266.3Intense
276.3Intense
286.4Intense
296.4Intense
306.4Intense
Planning a trip in September

Hazard calendar for São Luís

In seasonPeak

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

São Luís's monsoon runs January–May, 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 São Luís?

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

7.0
Sightseeing
1st-best month of the year
8.5
Beach & pool
1st-best month of the year

September is one of the better times to visit São Luís for general sightseeing. The water and warmth also suit a beach or pool day.

What to pack for São Luís in September

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

In September, São Luís sees daytime highs around 29°C and nights near 26°C. Pack light clothes and sun protection. Worth having: a windbreaker. About 3 days see rain.

light clothessun protectiona windbreaker

Sea temperature near São Luís in September

The nearest coast averages about 28°C in September — the other half of the beach question. The full-year curve and swim-comfort zones are below.

The sea at the nearest coast (about 13 km away) is warmest in May at about 29°C and coldest in October near 28°C.

The water stays above 20°C all year — warm enough for a swim any month.

26°28°30°JanFebMarAprMayJunJulAugSepOctNovDecwarmtropicalcomfortable to swim
Sea temperature (°C)Comfort
Jan28Tropical
Feb28Tropical
Mar28Tropical
Apr29Tropical
May29Tropical
Jun29Tropical
Jul28Tropical
Aug28Tropical
Sep28Warm
Oct28Warm
Nov28Warm
Dec28Warm

UV index in São Luís in September

LowModerateHighVery highExtreme

Clear-sky midday UV in September peaks around 12 (very high — sun protection essential). The full-year curve, shaded by WHO exposure level, is below.

Under clear skies, the midday UV index in São Luís peaks around March 17 at about 15 (extreme) — sunscreen, a hat and midday shade are essential. It bottoms out near July 17 at about 10 (extreme).

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

025710JanFebMarAprMayJunJulAugSepOctNovDecExtremeMar 17UV 15Jul 17UV 10
UV index (midday)Level
Jan13Extreme
Feb14Extreme
Mar16Extreme
Apr14Extreme
May12Extreme
Jun10Extreme
Jul10Very high
Aug10Extreme
Sep12Extreme
Oct12Extreme
Nov11Extreme
Dec11Extreme

Air quality in São Luís 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 São Luís is worst in February — around 18 µg/m³ PM2.5 (moderate), about 2.7× the cleanest month (July, 7 µg/m³).

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

0102030JanFebMarAprMayJunJulAugSepOctNovDecModerateGoodFeb 2018 µg/m³Jul 157 µg/m³
PM2.5 (µg/m³)Level
Jan14Moderate
Feb18Moderate
Mar18Moderate
Apr13Moderate
May8Good
Jun7Good
Jul7Good
Aug8Good
Sep9Good
Oct10Good
Nov10Good
Dec11Good
Location & terrain

Where is São Luís?

São Luís sits at 2.5°S, 44.3°W, 29 m above sea level, in Brazil. The nearest listed city is Alcântara, 19 km away.

Topography around São Luís

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

Within 3 km, the terrain around São Luís has only modest variations in elevation — a maximum elevation change of 37 m around an average of 8 m above sea level; within 16 km, only modest variations in elevation — a maximum elevation change of 65 m; within 80 km, only modest variations in elevation — a maximum elevation change of 102 m.

The land around São Luís is covered by artificial surfaces (38%) and water (33%) within 3 km, water (52%) and trees (20%) within 16 km, and water (36%) and trees (35%) within 80 km.

3 km
37 m
16 km
65 m
80 km
102 m
treesshrubsgrasslandartificial surfacesbare terrainwaterwetlandmangroves
September weather nearby: Alcântara 19 km · Paço do Lumiar 22 km · Raposa 25 km · São José de Ribamar 27 km · Icatu 38 km · Rosário 46 km · Morros 47 km · Bacabeira 49 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 São Luís (-2.5297°, -44.3028°, elevation 29 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. Sea temperatures are the NOAA OISST v2.1 1991–2020 monthly climatology (public domain), sampled at the nearest ocean point. 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).