September Weather in Ko Samui, Thailand

Last updated: August 27, 2025

In September, Ko Samui, Thailand experiences a warm and humid tropical climate, with average temperatures hovering around 28°C (82°F). The month sees maximum highs reaching up to 30°C (86°F), while nighttime lows dip to a comfortable 26°C (78°F). However, visitors should be prepared for considerable rainfall, averaging 151 mm (5.9 in) over approximately 21 days, contributing to the island's lush scenery. With humidity levels at a high 87%, September is a time of vibrant nature, albeit with frequent showers that dance through this beautiful paradise, offering an authentic experience of tropical living.

September Temperature in Ko Samui

September in Ko Samui, Thailand, offers a delightful tropical embrace, with temperatures ranging from a cozy 26°C (78°F) at night to a pleasant 30°C (86°F) during the day. The average temperature hovers around 28°C (82°F), creating an ideal environment for both relaxation and adventure. As the monsoon season approaches, you may notice a slight dip in maximum temperatures from the summer peaks, but the overall warmth remains inviting. With the backdrop of soft ocean breezes, September is a charming time to explore the island's stunning beaches and lush greenery, all while enjoying the characteristic warmth that defines this stunning tropical paradise.

September Weather in Ko Samui: Daily Temperature Highs, Lows, and Averages

The chart illustrates September temperature patterns in Ko Samui, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends. In Ko Samui, September typically has an average temperature of {2}°C ({3}°F), with highs reaching up to {4}°C ({5}°F) and lows dropping to around {6}°C ({7}°F).
JanFebMarAprMayJunJulAugSepOctNovDec808182838383838282818180
Data source: Temperature data for Ko Samui generated using information from the Copernicus Climate Change Service.
Choose your preferred temperature unit
The average of daily temperatures (24 hours) calculated across all days in the month.

September Precipitation in Ko Samui

September in Ko Samui, Thailand, marks a significant uptick in rainfall, with precipitation reaching 151 mm (5.9 in) and occurring over 21 days of the month. This surge heralds the onset of the wet season, setting it apart from the preceding months, which generally experience less moisture. While January to August typically see limited rainfall with totals under 80 mm, September paves the way for heavier downpours, foreshadowing an even wetter October with 241 mm (9.5 in) expected. This trend suggests that travelers might encounter the lush, vibrant landscapes characteristic of the region, albeit with the frequent showers that define the September climate. As the island shifts into the heart of the rainy season, preparations for more rain will be essential for both locals and visitors alike.

September Precipitation Trends in Ko Samui

The chart displays monthly precipitation patterns in Ko Samui, with values for each month alongside September’s data, which is highlighted for easy comparison. It shows the amount of precipitation, providing insights into how September’s conditions compare to those of other months. In Ko Samui, September typically receives around {2} mm ({3} inches) of precipitation spread over approximately {4} days.
JanFebMarAprMayJunJulAugSepOctNovDec1443938144126967980151241336207
Data source: Precipitation data for September generated using information from the Copernicus Climate Change Service.
Choose your preferred precipitation unit

September Humidity in Ko Samui

September in Ko Samui, Thailand, marks a peak in humidity, averaging an impressive 87%. This period transitions from the more moderate levels seen earlier in the year, where January through April hover around the low 70s. As the year progresses, humidity levels rise significantly, particularly in the rainy season from May to August, culminating in the high humidity of September. Following this peak, levels slightly decrease in October but remain relatively high at 86%. It's clear that visitors to Ko Samui in September should prepare for a sticky tropical experience, highlighting the island’s lush landscape and vibrant atmosphere.

September Average Humidity in Ko Samui

This chart illustrates the average monthly humidity levels in Ko Samui, with September’s data highlighted for easy comparison. It shows the fluctuation in humidity throughout the year, helping you understand how conditions vary by season. In September, average humidity in Ko Samui is approximately {2}%, offering insight into how humid the weather typically is during this month.
JanFebMarAprMayJunJulAugSepOctNovDec72%68%68%69%77%86%86%88%87%86%87%84%
Data source: Humidity data for September generated using information from the Copernicus Climate Change Service.

September UV Index in Ko Samui

As September rolls into Ko Samui, Thailand, the UV index remains a consistent 14, maintaining the extreme exposure category that characterizes much of the year in this tropical paradise. The steady UV levels from June through October demonstrate an unyielding sun that demands respect. With a burn time of just 10 minutes, visitors and locals alike must prioritize sun protection to shield themselves from potential skin damage. Historical data shows that the UV index peaks slightly in the warmer months of March and April but remains elevated throughout the late summer and early fall. As you plan your outdoor adventures, remember to stay informed and protected against these intense rays. For more detailed information and tips on sun safety, check out Ko Samui UV Index.

Maximum UV Index Levels in Ko Samui for September

The chart shows the monthly maximum UV Index (UVI) for Ko Samui in September, representing the highest UV radiation level. The UVI measures the intensity of ultraviolet radiation from the sun, indicating the potential risk of sunburn and UV-related health issues. In September, the maximum UV index in Ko Samui typically reaches {2}, which falls under the {3} exposure category.
JanFebMarAprMayJunJulAugSepOctNovDec111415151413141414141111
Data source: Ko Samui September UVI data generated using information from the Copernicus Climate Change Service.

UV Risk Categories

  •  Extreme (11+): Avoid the sun, stay in shade.
  •  Very High (8-10): Limit sun exposure.
  •  High (6-7): Use SPF 30+ and protective clothing.
  •  Moderate (3-5): Midday shade recommended.
  •  Low (0-2): No protection needed.

September Sunshine in Ko Samui

In September, Ko Samui experiences a gentle decline in sunshine hours, tallying 286 hours of sun, compared to the previous months. This slight drop continues the trend seen in August, with the onset of the wetter season as the islands prepare for the upcoming rainy months. Despite the decrease, September's sunshine still offers ample opportunities for beachgoers and adventurers, providing a warm and inviting backdrop for those seeking to indulge in the island's natural beauty. As the sunshine begins to wane, visitors can revel in a blend of warm days and cooler evenings, making it a splendid time to explore the vibrant culture and tranquil landscapes of this tropical paradise.

Monthly Sunshine Duration in Ko Samui: September Highlighted

The September sunshine duration represents the total number of hours Ko Samui experiences direct sunlight during the month of September, excluding cloudy or obstructed periods. This chart compares the sunshine duration of September with the other months of the year.
JanFebMarAprMayJunJulAugSepOctNovDec252h308h346h318h331h308h314h300h286h287h289h302h
Data source: Ko Samui September Sunshine duration data generated using information from the Copernicus Climate Change Service.

Chance of Sun in Ko Samui During September

When planning a trip to Ko Samui, Thailand, one should be mindful of the weather patterns, especially in September. This month sees a slim chance of sunny days, with only an 11% likelihood of sunshine, making it one of the cloudiest months of the year. As the monsoon season approaches, the trend shows a significant drop in sunny weather from earlier months like February (58%) and March (51%) to **August's bleak 9%. This pattern suggests that travelers seeking bright skies may want to consider visiting outside of September to enjoy the island's sunshine to the fullest.

Percentage of Sunny Days in September in Ko Samui

The chart illustrates the percentage of sunny days in Ko Samui throughout the year, with September highlighted. It highlights the variation in sunshine across each month and provides an overview of the typical frequency of sunny days, offering insights into how often Ko Samui experiences clear skies throughout the year.
JanFebMarAprMayJunJulAugSepOctNovDec32%58%52%32%21%22%18%9%11%11%8%39%
Data source: Ko Samui September chance of sun data, generated using information from the Copernicus Climate Change Service.

Daylight Hours in Ko Samui in September

In September, Ko Samui, Thailand enjoys a consistent 12 hours of daylight, mirroring the trend established during the mid-year months. This balanced daylight duration follows the peak of summer, where the sun graces the island with long, luminous days from March through August. As the year turns towards October, daylight begins to gradually taper to 11 hours, echoing the patterns observed in January and February. This continuity of nearly half the year spent under 12 hours of daylight sets a rhythm that enhances the island's vibrant atmosphere, making it an ideal destination for sun-seekers and adventurers alike.

Average Daylight Hours in Ko Samui for September

The chart illustrates the variation in daylight duration in Ko Samui throughout the year, with September highlighted. It shows the monthly changes in daylight hours, calculated by summing the hours between sunrise and sunset.
JanFebMarAprMayJunJulAugSepOctNovDec11h 37m11h 48m12h 3m12h 19m12h 32m12h 39m12h 36m12h 24m12h 9m11h 53m11h 40m11h 33m
Data source: Ko Samui daylight hours, calculated by summing the hours between sunrise and sunset for each day.

September Winds in Ko Samui

As September rolls into Ko Samui, the charming island experiences a gentle exhale of wind, with an average speed of 4.5 m/s (10 mph). This slight dip from the more vigorous gusts of July and August reflects a transition into the quieter, more serene part of the year. While the wind slows, it maintains a delightful presence, perfect for enjoying the island's idyllic beaches and lush landscapes. Looking back, the wind speeds have generally traveled a path of higher activity earlier in the summer, ranging from 5.2 m/s in January to that peak in July, before gradually easing. As the month of September unfolds, it offers a unique blend of calmness, inviting visitors to relax and soak in the enchanting surroundings, with beyond-stable conditions that are characteristic of the soft, whispering winds typical of this time of year.

Average September Wind Speed in Ko Samui

The chart displays monthly wind speed patterns in Ko Samui, with values for each month shown alongside September's data, which is highlighted for easy comparison. It illustrates the average wind speed, offering insights into how September's wind conditions compare to the rest of the year.
JanFebMarAprMayJunJulAugSepOctNovDec5.25.04.63.54.04.85.44.74.5 m/s4.75.05.4
Data source: Ko Samui September wind data, generated using information from the Copernicus Climate Change Service.

How September Weather in Ko Samui Compares to Other Months

Weather in Ko Samui varies notably across the year, with each month offering distinct climate conditions. This page compares September’s weather to other months in Ko Samui, focusing on differences in temperature, rainfall, humidity, and UV levels.

When comparing the weather in September and January, we can see some notable differences. September tends to be slightly warmer, with average temperatures around 28°C (82°F), compared to January's average of 27°C (80°F). However, September is also marked by much higher humidity at 87%, while January experiences a more comfortable humidity level of 72%. Additionally, September receives more precipitation, with 151 mm (5.9 in) spread over 21 days, whereas January sees 144 mm (5.7 in) over just 13 days. For more detailed insights about January weather, you can check out Ko Samui weather in January.

When comparing the weather in September and February, one can observe notable differences. In September, temperatures are slightly higher, with averages around 28°C (82°F) and maximums reaching 30°C (86°F), accompanied by high humidity levels at 87%. This month also experiences significant rainfall, with 151 mm (5.9 in) of precipitation over 21 days, making it one of the wetter months. In contrast, February sees slightly cooler temperatures, with averages of 27°C (81°F) and maximums of 28°C (83°F). The precipitation drops dramatically to just 39 mm (1.5 in) over 8 days, and humidity levels also decrease to 68%, creating a more comfortable and drier atmosphere. For more information, visit Ko Samui weather in February.

In September, the weather tends to be quite humid and rainy, with an average temperature of 28°C (82°F) and high humidity levels reaching 87%. The monthly rainfall amounts to 151 mm (5.9 in) spread over 21 days, emphasizing the wet nature of this month. In contrast, March offers a similar temperature range, with an average of 28°C (82°F) and a minimum of 25°C (78°F), but it is significantly drier, receiving only 38 mm (1.5 in) of precipitation over just 7 days. The humidity in March is also lower at 68%, making it a more comfortable time to enjoy outdoor activities. For a more detailed look at the weather specifics, you can check Ko Samui weather in March.

In comparing the weather of September and April, we see that both months feature warm temperatures, with September showing a slightly higher average of 28°C (82°F) compared to April's 28°C (83°F). However, April tends to have a higher maximum temperature of 31°C (88°F) versus September's maximum of 30°C (86°F). Precipitation is similarly significant, with September experiencing 151 mm (5.9 in) over 21 days, while April sees slightly less at 144 mm (5.7 in) over 15 days. Notably, the humidity is markedly higher in September at 87%, compared to a more comfortable 69% in April. For a detailed look at the April weather, you can check Ko Samui weather in April.

When comparing the weather in September and May, both months feature warm temperatures with minimal differences; September sees a minimum temperature of 26°C (78°F) and an average of 28°C (82°F), while May has similar minimum and average temperatures but can reach slightly higher maximums at 32°C (89°F). In terms of precipitation, September experiences more rainfall, totaling 151 mm (5.9 in) over 21 days, compared to May's 126 mm (5.0 in) over 22 days. Additionally, the humidity level is higher in September at 87%, while May is more comfortable with a humidity of 77%. For a detailed look at the weather patterns, check out Ko Samui weather in May.

September and June exhibit similar temperature patterns, with minimum temperatures around 26°C (78°F) and average temperatures lingering between 28°C (82°F). However, June tends to be slightly warmer, reaching maximum temperatures of 32°C (89°F) compared to September's peak of 30°C (86°F). In terms of precipitation, September is notably wetter, receiving 151 mm (5.9 in) over 21 days, while June sees less rain at 96 mm (3.8 in) over 18 days. Humidity levels are also comparable, with September at 87% and June at 86%. For a more detailed look at June weather, you can check Ko Samui weather in June.

In comparing the weather of September to that of July, we see some notable differences. Both months feature similar minimum temperatures, around 26°C (78°F), and average temperatures hovering between 28°C (82°F) and 29°C (83°F). However, July tends to be slightly warmer at its maximum temperature of 31°C (88°F), compared to September's maximum of 30°C (86°F).

Rainfall also distinguishes the two months; September experiences significantly more precipitation, with 151 mm (5.9 in) spread over 21 days, while July sees only 79 mm (3.1 in) over 17 days. Both months maintain high humidity levels, with September at 87% and July at 86%. For more details, you can check Ko Samui weather in July.

In comparing the weather between September and August, both months exhibit similar temperature ranges, with September recording a minimum of 26°C and a maximum of 30°C, while August has slightly higher maximums at 31°C. Humidity levels hover around 87% in September, closely matching August's 88%. Notably, September experiences significantly more precipitation, totaling 151 mm over 21 rainy days compared to August's 80 mm over 18 days. For a detailed look at August's weather conditions, check out Ko Samui weather in August.

In comparing the weather of September and October, September experiences slightly higher average temperatures with a minimum of 26°C (78°F) and a maximum of 30°C (86°F), while October sees a marginally cooler average of 27°C (81°F). However, October is marked by significantly increased rainfall, with precipitation levels rising to 241 mm (9.5 in) over 28 days compared to September's 151 mm (5.9 in) over 21 days. Humidity remains similar between the two months, with September at 87% and October slightly lower at 86%. For more detailed insights, you can check Ko Samui weather in October.

In September, temperatures range from a minimum of 26°C (78°F) to a maximum of 30°C (86°F), with an average of 28°C (82°F). The month experiences significant rainfall, with a total of 151 mm (5.9 in) spread over 21 rainy days and a humidity level holding steady at 87%. In contrast, November sees slightly cooler temperatures, with lows of 25°C (77°F) and highs reaching 29°C (85°F), averaging around 27°C (81°F). However, November is considerably wetter, receiving 336 mm (13.2 in) of precipitation over 24 days, while maintaining the same high humidity of 87%. For more detailed information about weather conditions, check out Ko Samui weather in November.

September weather in Ko Samui is characterized by warmer temperatures, with averages reaching around 28°C (82°F) and maximums hitting 30°C (86°F). The month experiences significant rainfall, totaling 151 mm (5.9 in), spread over 21 days, contributing to a humid atmosphere with 87% humidity. In contrast, December brings slightly cooler temperatures with an average of 27°C (80°F) and maximums of 29°C (84°F). However, it sees increased precipitation, totaling 207 mm (8.1 in) over 17 days, while the humidity remains relatively high at 83%. For a detailed look at December's weather patterns, visit Ko Samui weather in December.

Compare Ko Samui's Climate with Cities Worldwide

Conclusion: What to Expect From September Weather in Ko Samui

As September rolls in, Ko Samui's weather takes on a unique character that sets it apart from other months. With temperatures averaging around a comfortable 28°C, this tropical paradise experiences a noticeable increase in rainfall, leading to lush landscapes and a vibrant atmosphere. The high humidity coupled with frequent showers means that while the sun may hide behind clouds, the air remains warm and inviting. September is one of the wettest months, showcasing the island's rejuvenating beauty, perfect for those seeking a quieter, more serene escape. For a detailed look at what the rest of the year has to offer, don't miss the Ko Samui Climate page.