São Luís
Brazil
Long-term weather forecast
Long-term weather forecast

September weather forecast and climate
São Luís, Brazil

The first month of the spring, September, is also a hot month in São Luís, Brazil, with average temperature fluctuating between 31°C (87.8°F) and 23.5°C (74.3°F).
The ideal sea water temperature of 27.3°C (81.1°F) and only 2 rainfall days, with 23.3mm (0.9") of accumulated rainfall, make September the best time for swimming and other water activities.

Temperature

In September, the average high-temperature in São Luís is almost the same as in August - a still tropical 31°C (87.8°F). The average low-temperature, in São Luís, is 23.5°C (74.3°F).

Heat index

The average heat index is calculated to a blistering 41.2°C (106.2°F). Beware - heat cramps and heat exhaustion are very likely. Heatstroke is imminent with prolonged activity.
Note that heat index values are valued for light wind and location in the shade. With the exposure to direct sunlight, the heat index may be increased by up to 15 Fahrenheit (8 Celsius) degrees.
Note: The heat index, also known as 'apparent temperature', 'real feel', 'felt air temperature', or 'feels like', is an index that combines air temperature and relative humidity to determine the human-perceived temperature equivalent. This effect is subjective, depending on the activity and individual's heat perception influenced by various reasons (clothing, differences in body mass, height, and shape, metabolic differences). Bear in mind that direct sunshine exposure increases weather impact, and may raise heat index by up to 15 Fahrenheit (8 Celsius) degrees. Heat index values are especially crucial for babies and toddlers. Children are often less aware of the need to rest and re-hydrate. Thirst is a late sign of dehydration - it is vital to remain hydrated, particularly during prolonged physical activities.
The human body normally cools itself by perspiration. Excessive warmth is eliminated from the body by evaporation of sweat. When the relative humidity is high, the evaporation rate is reduced. The warmth is removed from the body at a lower rate, causing the body to retain more heat than it would in dry air. If the body can not disperse the excessive heat and body temperature reaches conditions of hyperthermia, above 37.5°C (99.5°F) to 38.3°C (100.9°F), thermal conditions are potentially life-threatening.

Humidity

In São Luís, the average relative humidity is 81%.

Rainfall

In São Luís, in September, it is raining for 2 days, with typically 23.3mm (0.9") of accumulated precipitation. Throughout the year, there are 130 rainfall days, and 2290.2mm (90.2") of precipitation is accumulated.

Sea temperature

The month with the coldest seawater is September, with an average sea temperature of 27.3°C (81.1°F).
Note: For any water activity, surface water temperatures between 25°C (77°F) and 29°C (84.2°F) are considered as excellent and extremely pleasant for lengthened periods.

Daylight

In São Luís, the average length of the day in September is 12.1h.

Sunshine

The average sunshine in São Luís, Brazil, is 8.3h.

UV index

January through April, September through December, with an average maximum UV index of 12, are months with the highest UV index. A UV Index value of 11, and more, symbolizes an ultimate health vulnerability from unprotected exposure to the Sun's UV rays for ordinary individuals.
Note: The average daily UV index of 12 transform into the following instructions:
Practice all-important precautions. Light skin people may get burned in less than 5 minutes. Seek shade and minimize exposure to direct Sun in a period between 10 a.m. and 4 p.m. when UV radiation is most intense; keep in mind that shade structures like parasols or canopies do not provide perfect sun protection. On bright days sunglasses that block both UVA and UVB rays should be worn. A hat with a wide brim is extremely helpful, as it can prevent roughly 50% of UV radiation from reaching the eyes. A broad-spectrum sunscreen of SPF 30+ should be liberally applied and re-applied every two hours, and immediately after an outdoor workout or a swim. Beware! The reflection of water and sand dramatically increases exposure to the UV rays.

What is the temperature in September in São Luís?

In São Luís, in September, the average high-temperature is 31°C (87.8°F), and the average low-temperature is 23.5°C (74.3°F). The average heat index (a.k.a. 'felt air temperature', 'real feel'), that takes the relative humidity and factores it into the air temperature reading, in September is appraised at 41.2°C (106.2°F).

What is the average humidity in September in São Luís?

The average relative humidity in September in São Luís, Brazil, is 81%.

How many days does it rain in September in São Luís?

In September, in São Luís, Brazil, the rain falls for 2 days. Throughout September, 23.3mm (0.9") of precipitation is accumulated.

What is the month with the coldest sea water in São Luís?

September is the month with the coldest seawater in São Luís, Brazil, with an average sea temperature of 27.3°C (81.1°F).

What is the sea water temperature in September in São Luís?

In São Luís, Brazil, the average seawater temperature in September is 27.3°C (81.1°F). Water temperature between 25°C (77°F) and 29°C (84.2°F) is regarded as very warm and enjoyable by all. With these temperatures, water activities are pleasurable, without feeling uncomfortable for prolonged periods.

What is the average length of the day in September in São Luís?

The average length of the day in September is 12.1h.

How long on average sun shines in September in São Luís?

In São Luís, Brazil, the average sunshine in September is 8.3h.

What is the month with the highest UV index in São Luís?

Months with the highest UV index in São Luís are January through April, September through December, with an average maximum UV index of 12.

What is the UV index reading in September in São Luís?

In São Luís, Brazil, the average daily maximum UV index in September is 12. A UV Index of 11, and more, symbolizes an extreme health threat from the exposure to the Sun's UV rays.
Average temperature in September - São Luís, Brazil
  • Average high temperature in September: 31°C

The warmest month (with the highest average high temperature) is November (31.4°C).
Months with the lowest average high temperature are February and March (29.4°C).

  • Average low temperature in September: 23.5°C

Months with the highest average low temperature are November and December (24°C).
The coldest month (with the lowest average low temperature) is July (22.6°C).

Average humidity in September - São Luís, Brazil
  • Average humidity in September: 81%

The month with the highest relative humidity is April (90%).
The month with the lowest relative humidity is December (71%).

Average rainfall in September - São Luís, Brazil
  • Average rainfall in September: 23.3mm

The wettest month (with the highest rainfall) is April (475.9mm).
The driest month (with the lowest rainfall) is October (7.6mm).

Average rainfall days in September - São Luís, Brazil
  • Average rainfall days in September: 2 days

The month with the highest number of rainy days is March (23 days).
Months with the lowest number of rainy days are October and November (1 days).

Average sea temperature in September - São Luís, Brazil
  • Average sea temperature in September: 27.3°C

The best month for swimming (with the highest average sea temperature) is March (28.9°C).
The coldest month (with the lowest average sea temperature) is September (27.3°C).

Average daylight in September / Average sunshine in September - São Luís, Brazil
  • Average daylight in September: 12.1h

Months with the longest days are January and December (Average daylight: 12.3h).
Months with shortest days are May, June, July and August (Average daylight: 12h).

  • Average sunshine in September: 8.3h

The month with most sunshine is August (Average sunshine: 8.4h).
The month with least sunshine is March (Average sunshine: 3.5h).

Average UV index in September - São Luís, Brazil
  • Average UV index in September: 12

Months with the highest UV index are January, February, March, April, September, October, November and December (UV index 12).
Months with the lowest UV index are June and July (UV index 10).