Ko Samui
Thailand
Long-term weather forecast
Long-term weather forecast

September weather forecast and climate
Ko Samui, Thailand

The scenic view of the striking Angthong National Marine Park in Ko Samui, Thailand, calm clear water all around
The scenic view of the striking Angthong National Marine Park in Ko Samui, Thailand, calm clear water all around
September, the first month of the autumn, in Ko Samui, is still a hot month, with average temperature varying between 24.8°C (76.6°F) and 30.5°C (86.9°F).

Temperature

In Ko Samui, the average high-temperature in September is relatively the same as in August - a still hot 30.5°C (86.9°F). In September, in Ko Samui, the average low-temperature is 24.8°C (76.6°F).

Heat index

The average heat index is estimated at a sweltering 39.2°C (102.6°F). Take extra precautions, as heat cramps and heat exhaustion are possible. Sustained activity may result in heatstroke.
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', 'feels like', 'felt air temperature', or 'real feel', is what the temperature feels like to the human body when the air temperature is combined with the relative humidity. Additional factors like clothing, metabolic differences, wind, and activity influence one's weather impression. 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. Young children are generally more endangered than adults, as they usually less sweat. And also, due to larger skin surface relative to their small bodies and higher heat production as a result of their activity.
The human body normally cools itself by perspiration, as evaporated sweat carries heat away from the body. A higher relative humidity affects normal body cooling by reducing the evaporation rate, subsequently lowering the rate at which the body cools and increasing the perception of heat. 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 is 80%.

Rainfall

In Ko Samui, during September, the rain falls for 16 days and regularly aggregates up to 121.7mm (4.8") of precipitation. In Ko Samui, during the entire year, the rain falls for 160 days and collects up to 1960.1mm (77.2") of precipitation.

Sea temperature

In Ko Samui, the average seawater temperature is 29.2°C (84.6°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

The average length of the day in September is 12.2h.

Sunshine

May through December, with an average of 6h of sunshine, are months with the least sunshine.

UV index

February through October, with an average maximum UV index of 12, are months with the highest UV index in Ko Samui. A UV Index reading of 11, and higher, represents an excessive health risk from unsafe exposure to the UV radiation for the ordinary person.
Note: The daily maximum UV index of 12 in September interpret into the following advice:
Take all necessary precautions, as unprotected skin can burn in 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 Ko Samui?

In September, in Ko Samui, the average high-temperature is 30.5°C (86.9°F), and the average low-temperature is 24.8°C (76.6°F). In September, the average heat index (a.k.a. 'felt air temperature', 'real feel'), that combines air temperature and relative humidity, is appraised at 39.2°C (102.6°F).

What is the average humidity in September in Ko Samui?

In September, the average relative humidity in Ko Samui is 80%.

How many days does it rain in September in Ko Samui?

In Ko Samui, Thailand, in September, it is raining for 16 days, with typically 121.7mm (4.8") of accumulated precipitation.

How warm is the water in September in Ko Samui?

In Ko Samui, Thailand, in September, the average water temperature is 29.2°C (84.6°F). For swimming, diving, and other water activities, temperatures between 25°C (77°F) and 29°C (84.2°F) are perceived as very enjoyable and pleasurable for prolonged periods without feeling uncomfortable.

How many hours of daylight does Ko Samui have in September?

The average length of the day in September in Ko Samui is 12.2h.

What is the month with the least sunshine in Ko Samui?

May through December, with an average of 6h of sunshine, are months with the least sunshine in Ko Samui.

How long on average sun shines in September in Ko Samui?

In September, the average sunshine is 6h.

What are the months with the highest UV index in Ko Samui?

February through October, with an average maximum UV index of 12, are months with the highest UV index in Ko Samui, Thailand.

What is the UV index intensity in September in Ko Samui?

The average daily maximum UV index in September in Ko Samui, Thailand, is 12. A UV Index of 11, and more, symbolizes an extreme health vulnerability from the exposure to the Sun's UV rays.
Average temperature in September - Ko Samui, Thailand
  • Average high temperature in September: 30.5°C

The warmest month (with the highest average high temperature) is April (32.6°C).
The month with the lowest average high temperature is January (29°C).

  • Average low temperature in September: 24.8°C

The month with the highest average low temperature is April (26.1°C).
The coldest month (with the lowest average low temperature) is December (23.9°C).

Average humidity in September - Ko Samui, Thailand
  • Average humidity in September: 80%

Months with the highest relative humidity are October and November (85%).
Months with the lowest relative humidity are June, July and August (78%).

Average rainfall in September - Ko Samui, Thailand
  • Average rainfall in September: 121.7mm

The wettest month (with the highest rainfall) is November (506.6mm).
The driest month (with the lowest rainfall) is February (54.4mm).

Average rainfall days in September - Ko Samui, Thailand
  • Average rainfall days in September: 16 days

Months with the highest number of rainy days are October and November (20 days).
The month with the lowest number of rainy days is March (4 days).

Average sea temperature in September - Ko Samui, Thailand
  • Average sea temperature in September: 29.2°C

The best month for swimming (with the highest average sea temperature) is May (30.1°C).
The coldest month (with the lowest average sea temperature) is January (27.8°C).

Average daylight in September / Average sunshine in September - Ko Samui, Thailand
  • Average daylight in September: 12.2h

The month with the longest days is June (Average daylight: 12.7h).
Months with shortest days are January and December (Average daylight: 11.6h).

  • Average sunshine in September: 6h

The month with most sunshine is February (Average sunshine: 9h).
Months with least sunshine are May, June, July, August, September, October, November and December (Average sunshine: 6).

Average UV index in September - Ko Samui, Thailand
  • Average UV index in September: 12

Months with the highest UV index are February, March, April, May, June, July, August, September and October (UV index 12).
The month with the lowest UV index is December (UV index 10).