December weather forecast
São Luís, Brazil

The climatic conditions in December represent an upswing towards São Luís's rainy season with an increase in rainfall levels to 77mm (3.03"). As temperatures maintain a familiar range, daylight hours remain consistent with preceding months at 12.3 hours. Interestingly, the UV index descends to 12, matching the values from the start of the year. December serves as a prelude to São Luís's wet period with a significant leap in rainfall levels, wrapping the city in a distinctly humid and warm atmosphere.

Temperature

The commencement of December in São Luís notes an average high-temperature of a still hot 31.1°C (88°F), exhibiting little difference from the previous month. During December, São Luís records an average temperature of 24°C (75.2°F) at night.

Heat index

Throughout December, the heat index is appraised at a very hot 38°C (100.4°F). Take more caution, heat exhaustion and heat cramps may occur. Long-lasting activity may cause heatstroke.
Take into consideration that the heat index values are calculated for shade and light wind conditions. The heat index has the possibility to be enhanced by 15 Fahrenheit (8 Celsius) degrees when there is direct sun exposure.
Note: The heat index, also known as 'apparent temperature' or 'feels like', shows a temperature sensation when both heat and moisture conditions are combined. The impact of temperature is individual, as people's perception of weather may change based on their body mass, height, and physical activity. Realize that direct exposure to sunlight can augment the felt heat, leading to a potential increase in the heat index by 15 Fahrenheit (8 Celsius) degrees. Heat index values are highly important for children. Children typically face more danger than adults as their sweat production is usually lower. Additionally, the bigger skin surface compared to their small size and the increased heat due to their activeness exacerbate the risk.
The body's natural response to excessive warmth is perspiration, as it allows for cooling through sweat evaporation. In the presence of elevated relative humidity, the evaporation rate decreases. This reduction leads to increased body heat retention compared to conditions of dry air. Exceeding the body's heat disposal threshold results in a rise in body temperature and potential thermal disorders.

Humidity

The least humid month is December, with an average relative humidity of 71%.

Rainfall

In São Luís, during December, the rain falls for 4 days and regularly aggregates up to 77mm (3.03") of precipitation. Throughout the year, there are 130 rainfall days, and 2290mm (90.16") of precipitation is accumulated.

Sea temperature

In December, the average sea temperature in São Luís, Brazil, is 28.1°C (82.6°F).
Note: For swimming, diving, or other water activities, the temperature range of 25°C (77°F) to 29°C (84.2°F) is perceived as exceptionally enjoyable and comfortable even for prolonged periods.

Daylight

December has the longest days of the year, with an average of 12h and 18min of daylight.
On the first day of December in São Luís, Brazil, sunrise is at 05:38 and sunset at 17:54. On the last day of the month, sunrise is at 05:52 and sunset at 18:08 -03.

Sunshine

The average sunshine in December in São Luís is 6.7h.

UV index

The months with the highest UV index are January through April, September through December, with an average maximum UV index of 12. A UV Index reading of 11, and higher, represents an extreme threat to health from unprotected exposure to Sun's UV rays for the ordinary person.
Note: A maximum high daily UV index of 12 during December translates into the following directions:
Employ every precaution of importance, unprotected skin and eyes could burn within moments. 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. A wide-brimmed hat is a shield, deflecting up to 50% of harmful UV radiation from eyes. Apply and frequently reapply a broad-spectrum SPF 30+ sunscreen after every two hours, or immediately after a swim or outdoor exercise. Caution! The Sun's UV intensity grows with reflections off sand and water.