September weather forecast
Colombo, Sri Lanka

The first month of the autumn, September, is still a warm month in Colombo, Sri Lanka, with an average temperature varying between 24.9°C (76.8°F) and 29.1°C (84.4°F).

Temperature

In September, the average high-temperature is essentially the same as in August - a still warm 29.1°C (84.4°F). In Colombo, Sri Lanka, in September, the average low-temperature is 24.9°C (76.8°F).

Heat index

The average heat index in September is estimated at a sweltering 35°C (95°F). Take special precautions - heat exhaustion and heat cramps are expected. Heatstroke may occur with lengthy activity.
Take into consideration that the heat index values are calculated for shade and light wind conditions. With 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 'real feel', 'feels like', 'felt air temperature', or 'apparent temperature', is a measure of how hot it feels when the actual air humidity is factored in. This effect is subjective, depending on the activity and individual's heat perception influenced by various reasons (metabolic differences, clothing, pregnancy). 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.
Perspiration is the human body's physiological response to high temperatures and is an attempt to lower body temperature through evaporation of sweat. With a lot of moisture in the air, the evaporation process is not as effective, and the body does not cool down as efficiently, creating a perception of overheating. When heat gain exceeds the level the body can remove, body temperature begins to rise, and heat-related illnesses and disorders may develop.

Humidity

In September, the average relative humidity in Colombo, Sri Lanka, is 81%.

Rainfall

In Colombo, Sri Lanka, in September, it is raining for 26.9 days, with typically 206mm (8.11") of accumulated precipitation. In Colombo, during the entire year, the rain falls for 289.4 days and collects up to 2262mm (89.06") of precipitation.

Sea temperature

In Colombo, in September, the average water temperature is 27.8°C (82°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 Colombo, the average length of the day in September is 12h and 10min.
On the first day of the month, sunrise is at 06:03 and sunset at 18:18. On the last day of September, sunrise is at 05:58 and sunset at 18:02 +0530.

Sunshine

The average sunshine in September in Colombo is 7.4h.

UV index

The months with the highest UV index in Colombo are January through April, July, September, November and December, with an average maximum UV index of 7. A UV Index of 6 to 7 symbolizes a high threat to health from unprotected exposure to Sun's UV rays for the average person.
Note: In September, the average maximum UV index of 7 translate into the following recommendations:
Take precautions against overexposure. Protection against sun damage is needed. The Sun's UV radiation is most powerful between 10 a.m. and 4 p.m. To the extent possible, limit exposure to the direct sun during these hours. 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. Beware! The strength of the UV rays is significantly increased by the reflection of the water and sand.