KOH SAMUI WEATHER SUMMARY
AVERAGE MONTHLY TEMPERATURES
AVERAGE MONTHLY HIGH / LOW TEMPERATURES
AVERAGE MONTHLY SEA / WATER TEMPERATURES
AVERAGE HOURS OF SUNSHINE
MONTHLY WEATHER SUMMARIES
JANUARY – Weather Summary
Koh Samui, Thailand’s third largest island, is an excellent tourist destination in January. The island enjoys a tropical climate throughout the year, which means that the temperature is constant throughout the year. Rainfall and cloud cover, however, vary drastically. In January, Koh Samui has an average daily high temperature of 28°C, while daily lows range around 24°C. Those daily highs and lows don’t vary much in the course of the month. Average highs rise slightly from 28°C to 30°C throughout the month, while average lows rise from 24°C to 25°C. January is the ‘coldest’ month and January 11 is historically the coldest day of the year. The average daily temperature in January is 26°C. Despite being the coldest month of the year, January days are still warm by all accounts. Especially around noon temperatures are hot and you can find relief in the warm tropical seas that surround the island. The sea temperature is a pleasant 26°C, as cold as the water ever gets in Koh Samui.
The length of the days is basically constant in January. January 1 is the shortest day of the year, with 11.34 hours of daylight, while January 31 is the longest, with 11.43 hours, a rise of only 9 minutes in the course of the month. January has an average of 7 hours of sunshine per day, just like December.
Cloud cover decreases significantly throughout the month. While at the beginning there is 78% of cloud cover, that number has fallen to 65% before the month is over. January 1 is the cloudiest day of the month; on January 31 the skies tend to be clearest.
January falls within the dry season in the resort and with clearing skies comes less rainfall. January receives an average of 90 mm of precipitation and has an average of 7 rainy days, making it the fourth-driest month, after March, February and April. This is considered dry by the island’s natives, who are used to much more precipitation during the monsoon season. The height of this wet season falls in November, which has no less than 430 mm of rainfall and 15 rainy days. The chance of precipitation decreases in the course of January. January 3 is the wettest day of the month, with a 37% chance of rainfall. With a chance of 26%, January 31 is the driest January day. You may experience three types of rainfall this month. The most likely one is light rain, which happens on 57% of those 7 rainy days. Moderate rain occurs on 28% days of precipitation, and thunderstorms happen on only one day in January. There are 9 fog days in January, the highest number in the year.
Because it is a tropical destination, the resort has an essentially constant amount of humidity throughout the year. In January, the humidity ranges around 85%, a percentage that doesn’t change in the course of the month.
Falling in the middle of the dry season, which is also the high season in the resort, January receives lots of tourists this time of year. The seas are calm now, and temperatures at their comfortable lowest. This is the best time to go diving and snorkelling.
FEBRUARY – Weather Summary
In Koh Samui, every month has excellent weather with nearly constant temperatures. However, there is some variation in weather types throughout the year. The island receives plenty of visitors all year round and February is no exception. February falls in the middle of the warm dry season and hot temperatures attract plenty of tourists, especially from Europe and North America, as their countries will be in the last month of the winter season.
In Koh Samui the average temperature in February is 27°C with an average high temperature of 29°C and an average low temperature of 25°C. Those daily highs and lows don’t change much in the course of the month. February 1 is the coldest day of the month, while February 28 is the warmest. There’s no real difference though, as temperatures rise barely one degree in the course of February. The sea water is also quite warm and has a comfortable average temperature of 27°C, which is one degree warmer than January.
Because February falls in the dry season, it is one of the driest months of the year. In fact, it is the second-driest, after March. February only gets a total of 30mm of rainfall in the course of the month, mostly occurring as short and heavy showers. There are only five days of precipitation in February. April has the same number of rainy days, while March has one day less. This means that holiday-makers can enjoy themselves on the beaches without having to worry too much about rain. However, this also means that there won’t be much rain to cool off the extremely warm afternoons. The chance of rainfall stays essentially constant throughout the month and varies between 24 and 26%. There is no increase or decrease to speak of. If it does rain, it is most likely to occur in the form of light rain. Light rain occurs on 65% of the days of rainfall. Other types of precipitation are moderate rain and thunderstorms, which can happen, but are unlikely. February does have a significant amount of foggy days: seven. Only March, December and January have more days of fog.
The humidity in February doesn’t change much either throughout February and stays around 85% on average. This is the average humidity from October through March.
Besides the temperatures, rainfall and humidity, there is a fourth weather factor that remains basically constant in February. The length of the days increases only by 12 minutes in the course of the month. February 1 is the shortest day of the month with 11.43 hours of daylight and February 28 is the longest with 11.56 daylight hours. Holiday-makers will also be treated to plenty of sunshine as Koh Samui receives an average 8 sunshine hours per day in February. This is one hour more than January and the highest number of sunshine hours in the year, a number that is shared with March and April.
There is one thing that does change significantly in the course of the month though. Cloud cover decreases quite a lot from the beginning of the month towards the end and is the main reason for the increase in sunshine hours. While February 1, the cloudiest day, has 62% of cloud cover, February 28, the clearest day, only has 48%.
MARCH – Weather Summary
March is one of the hottest months in Koh Samui’s calendar. It has to be said that every single month is warm in the resort though; temperatures don’t drop or rise much throughout the year. The tropical island was once a haven for backpackers, but has recently become one of Asia’s most popular seaside resorts, visited by tourists throughout the year, thanks to its excellent weather. March marks the end of the dry season and the beginning of the hot season. In March, Koh Samui has an average temperature of 29°C; only May is warmer. Average high temperatures for the island in March are 31°C and average low temperatures are around 26°C. These daily highs and lows don’t change at all in the course of the month. The beaches are one of the most popular hangouts on the island. Tourists don’t just spend their days on the beach because of the sun and the sand, but they also enjoy taking a swim in the warm waters as well, which have an average bath-like temperature of 27°C. The temperature of the sea doesn’t change much either in the course of the year. They generally fluctuate between 26°C and 28°C.
March has a daily average of eight hours of sunshine. This is the maximum number of sunshine hours in the year, which definitely has to do with less cloud cover during the dry season; February and April have the same amount, while May, when it gets rainier, experiences a sudden drop to only six hours of sunshine. The length of the days doesn’t change much in the course of March. March 1 is the shortest day of the month with 11.57 hours of daylight and March 31 is the longest with 12.12 daylight hours, a monthly increase of only 15 minutes.
Cloud cover is at its absolute lowest in March. It ranges around 47% throughout the month and doesn’t change substantially. Historically, March 16 is the clearest day of the year. To put into perspective how few cloud cover there actually is in March, know that in the beginning of February it was at a high of 65%, a percentage that will be reached again by April 26. The maximum amount of cloud cover is about 88%, which occurs from May through November.
The fact that there is not much cloud cover results in less precipitation as well. With a total of 30 mm of rainfall and only four rainy days, March is the driest month in Koh Samui. Only February comes close to this amount of dryness, also with 30 mm of rainfall, but with five days of rain. The average probability that you will experience rain during your visit in March is 26%. This number increases slightly in the course of the month. March 1 is the driest day with a 24% chance of rain, while March 31 is the wettest day with a chance of 27%. The most common type of precipitation in March is light rain, occurring on 55% of those four rainy days. Thunderstorms come in second, happening on 23% of the days of rainfall. The third type of precipitation is moderate rain, which is occurs on 17% of the rainy days. March does have eight days of fog though, the second-highest number of all months. Only January sees more foggy days and December has the same number.
The humidity in the resort in March averages around 85%, which is the case from October until the beginning of April. This percentage doesn’t vary at all in the course of the month.
March may just be the best time of year to visit the resort. Temperatures are high, as they always are, it is the driest month of the year, cloud cover is extremely low compared to any other month and it has an average of eight hours of sunshine, as much as you will ever experience in the resort.
APRIL – Weather Summary
Koh Samui is an extremely popular tourist destination in Thailand, thanks to its tropical climate. Temperatures are fairly constant all year round; the only variables are rainfall and cloud cover. April falls within the hot season and the resort has an average temperature of 29°C. Only May has a higher average temperature. The average daily high temperature in April is 32°C and the average low is 26°C, together with June making it the second-hottest month of the year after May. April is characterised by slightly rising high and low temperatures in the course of the month. The average high temperature on April 1 is 31°C; by the end of the month it has risen to 33°C. The month starts off with a daily low temperature of 26°C, a temperature that rises to 27°C by April 30. The sea temperature in April is 28°C, which stays that way through September. As is common with most resorts that enjoy tropical climates, the weather is usually hotter during the day and cooler at night, when a cold sea breeze cools things down a bit.
The length of the days in April is basically constant. With 12.13 hours of daylight, April 1 is the shortest day of the month. April 30 is the longest day, with 12.28 daylight hours. This 15-minute increase is not enough to call it significant. April has an average of eight hours of sunshine per day. This is the maximum amount of sunshine in the year, a number that is shared with February and March.
This high number of sunshine hours is due to relatively low cloud cover in April, although cloud cover does increase rapidly throughout the month. April 1 is by far the clearest day of the month, with 49% of cloud cover. There is a significant rise during the first week of the month. By April 7 there already is about 62% of cloud cover. April 30 has a cloud cover percentage of 68. The end of April marks the beginning of the cloudier, and therefore also wetter, part of the year.
April also sees a rise in the amount of rainfall, compared to the previous drier months of February and April. April has a total amount of 80mm of precipitation and five rainy days. It still is the third-driest month of the year though, but things are bound to change in May, which will suddenly get significantly wetter. April already sees an increase of rainfall in the course of the month. April 1 is the driest day of the month with a 28% chance of rainfall. April 30 is the wettest day with of chance of 36%. The two most common types of precipitation are light rain and thunderstorms, respectively occurring on 42% and 41% of the rainy days. The chance of thunderstorms increases greatly in the course of the month though. Luckily these storms are generally short-natured. In terms of fog, April is the fifth-foggiest month with a total six days of fog. April is the last (relatively) dry month in the year.
The humidity in the resort drops a little bit in April. While in March it was at 85%, now it ranges around 80%, which is still extremely humid by all accounts.
MAY – Weather Summary
May in Koh Samui is a pleasantly hot month, similar to April. May falls in the hot season and is the hottest month of the year on average. The average daily temperature is 30°C, one degree higher than April, June, July and August, the other hot season months. The average daily high temperature in May is 33°C, while the average daily low temperature is 26°C, both as high as they ever get on the island. The month is characterised by an almost perfectly constant temperature; there is hardly any noticeable difference between temperatures throughout the month. 50% of the days in May are classified as warm and the other 50% as hot. The sea is also comfortable warm with an average temperature of 28°C, as warm as the waters of the Gulf of Thailand get in the course of the year, perfect for swimming and other beach activities.
May sees a sudden drop in sunshine hours, as more clouds roll in and the weather gets wetter. While February, March and April had eight hours of sunshine, May only has six. The length of the days in May stays basically the same throughout the month. May 1 is the shortest day of the month with 12.28 hour of daylight; May 31 is the longest day with 12.38 daylight hours. This is an increase of only ten minutes, which is almost nothing. The length of the days is in fact pretty much constant year round. This is due to the resort’s location near the equator.
The biggest reason for the decrease in sunshine hours is the increase in cloud cover. The percentage of cloud cover rises rapidly in the course of the month. With 68% of cloud cover, May 1 is the clearest day of the month. This percentage climbs steadily and by May 31 cloud cover is 80%.
Although May falls in the hot season and temperatures are comparable to April, the increase in cloud cover results in a lot more rainfall than the previous dry months. May receives a total of 160mm of rainfall in the course of the month, which is double the amount of April. In terms of total rainfall, May is the third-wettest month in the year. Only October and November are (much) wetter. May has nine rainy days. While the hot season lasts until August, May marks the beginning of the wetter part of the year. Although this is not officially monsoon season – that season is from September to December – it does get significantly wetter all of a sudden. This period is sometimes called the mini-monsoon season. The chance of precipitation increases in the course of the month. May 1 is the driest day of the month with a 36% chance of rainfall. The wettest day is May 31 with a 49% chance of rain. The most likely type of precipitation in May is thunderstorms. They occur on 47% of the days of rainfall. The second-most common precipitation type is light rain, occurring on 41% of the rainy days.
The humidity is essentially constant in May, ranging around 80% each day. May has four days of fog.
JUNE – Weather Summary
June is usually regarded as the beginning of the peak tourist season in most beach resorts. Although the island of Koh Samui already receives plenty of tourists throughout the year, the number increases significantly in June as most students embark on their summer vacations.
The island experiences hot and wet weather throughout June. The average day temperature in June is 29°C, one degree less than May, which was the hottest month of the year. The average daily high temperature is 32°C and the daily low temperature is 26°C. This makes June the second-hottest month of the year, together with April. These average daily highs and lows don’t change in the course of the month and every day is as hot as the previous one. The sea temperature is still 28°C, which it has been since April and will stay until September.
June falls in the second part of the hot season, a part that is sometimes also called the mini-monsoon season. The total amount of rainfall in June is 100mm, which somehow is 60mm less than the previous month. The number of rainy days has stayed the same though. June has nine days of rainfall, which, of course, also means that there are 21 days without rain. The average probability that some type of precipitation occurs on any given day is 52% in June, a percentage that varies only slightly in the course of the month. June 1 tends to be the driest day of the month with a 49% chance of rainfall. June 31 is generally the wettest day with a 53% chance. The two most common types of precipitation in June are thunderstorms and light rain, which are observed on respectively 47% and 43% of the rainy days. These heavy storms and showers generally don’t last long and they are great to cool things down a little. The average humidity in June is 80% and doesn’t change much throughout the month. As a tropical destination, the island is always subject to high humidity. June has only three fog days, one day more than the absolute minimum of two days in September.
The June skies tend to be pretty cloudy and get even cloudier towards the end of the month. June 1 is the clearest day of the month with 81% of cloud cover; by June 31 that percentage has increased to 86%. Cloudy skies obviously also result in less sunshine. Although Ko Samui does get plenty of sunshine throughout the year, it is somewhat restricted by the clouds and rain. As such, the island only averages 6 hours of sunshine a day in June. This number of sunshine hours per day will stay the same all through the wet season, until the beginning of December.
The length of the days in June is constant. The shortest day of the month is June 1 with 12.39 hours of daylights. June 20 is the longest day of the month and also of the year and has 12.41 hours of daylight. By June 30 there is one minute less daylight, at 12.40 hours.
JULY – Weather Summary
The second half of the year kicks off in July. However, in the tropical Island of Koh Samui, the year-long tourist season is continuing as usual. Tourists planning to visit Koh Samui in July will be welcomed by hot and wet weather. The average temperature in July is 29°C. Only May is warmer. Average daily high temperatures range around 32°C, while the average daily lows are about 25°C. These average temperatures are perfectly constant throughout the month and are also fairly constant all year round. The heat may be unbearable though, especially around noon. Therefore, tourists are advised to go sightseeing in the mornings and evenings and to stay in the shade in the afternoon. They can, of course, also seek refuge in the warm waters of the Gulf of Thailand. The sea has an average temperature of a bath-like 28°C in July; the sea temperature doesn’t change much throughout the year.
July also has essentially constant day lengths. July 1 is the longest day of the month with 12.40 daylights hours, while July 31 is the shortest day with 12.32 hours of daylights, a decrease of merely eight minutes in the course of the month. This is due to the resort’s location near the equator. On average, sunshine can be enjoyed during only half of the day as an average July day has 6 hours of sunshine. This is in fact the case from May all through November. The reason for this is that the hot mini-monsoon season occurs between May and August and the actual, extremely wet, monsoon season from September to the beginning of December. This period of the year tends to be quite cloudy.
And July is cloudy indeed. With an average cloud cover of more than 86%, this is almost as cloudy as it ever gets in Ko Samui. The percentage of cloud cover in the course of the month doesn’t change much though, as it will stay this way to the end of November. On the other hand, July experiences very few fog days. With only three of those, it is the second-least foggiest month of the year. Fog tends to occur mostly in the dry season months, such as January, February and March. The humidity, however, is always high in a tropical destination like this. In July the average humidity ranges around 80%.
As said earlier, July falls within the mini-monsoon season, which is technically also still the hot season. The month receives a total of 120 mm of rainfall, occurring on nine rainy days. While the number of days of precipitation has stayed the same compared to June, the total amount has increased by 20 mm. Looking at the raw numbers, it can be concluded that July is the sixth-wettest month of the year, although most months that fall in the mini-monsoon season are very similar in terms of precipitation. The chance of rainfall doesn’t change much throughout the month. The average chance on any given day is 53%, a percentage that remains constant. The two most common type of precipitation are thunderstorms and light rain. Light rain occurs on 45% of the rainy days, while thunderstorms can be expected on 44% of the days of rainfall.
AUGUST – Weather Summary
August, just like all the other months in Koh Samui, is a hot month. Average temperatures during the month are around 27°C with daily average highs of 29°C and average low temperatures of 25°C, which all are exactly the same as July. With 60% of its days classified as warm and 40% as hot, August is the fourth-warmest month of the year. The average highs and lows don’t change much in the course of the month; they’re perfectly constant. On some days, especially around noon, the temperature tends to be a bit too hot. At these times, holiday-makers can take a long relaxing dip in the sea, which has an average temperature of 28°C throughout August. This comfortably warm sea temperature is the same from April through September.
As August falls in the middle of the wetter half of the hot season, it receives its fair share of rainfall. The total amount of precipitation in August is 100mm, 20mm less than July and the same as June. The number of rainy days has increased, though, compared with the previous months. August has ten days of rainfall. The chance of precipitation on any given day throughout the month is virtually constant. The average chance is 51%. Historically August 5 has the least chance of rainfall with 50% and August 13 the most with 53%, but these differences are extremely small. There are three types of precipitation in August: light rain, moderate rain and thunderstorms. Light rain is the most common type, occurring on 48% of those ten rainy days. Thunderstorms come in second with a 35% chance on a rainy day; and moderate rain occurs on 16% of the days of rainfall. August has four fog days, one day more than July and two days more than the absolute minimum of two days in September. The average humidity in August is 80%, a percentage that rises a couple of digits in the course of the month.
As rainfall and cloud cover are related, the amount of cloud cover doesn’t change much either in the course of the month. It stays very high all throughout August, averaging 87%, which it has been since June and will stay until November,
Cloud cover, of course, also greatly influences the amount of sunshine. August only has six hours of sunshine per day, a number it shares with the months between and including May and November, which incidentally is also the wetter half of the year. On average it is sunny for about half of a typical August day. These August days are essentially equally as long. August 1 is the longest day of the month with 12.32 hours of daylight, while August 31 is the shortest day of the month with 12.18 daylight hours, a small decrease of fourteen minutes in the course of the month.
SEPTEMBER – Weather Summary
The great thing about Koh Samui is that it experiences excellent weather all year round. The island resort, which is Thailand’s third-largest island, enjoys tropical weather. The temperatures are usually the same, but rainfall fluctuates drastically. September is the start of the monsoon season in Koh Samui and has an average temperature of 28°C, one degree less than June, July and August. The average daily high temperature in September is 31°C, while the average daily low is 25°C, which is still warm by all accounts. This daily highs and lows don’t change in the course of the month. 63% of all September days are classified as warm; 37% as hot. After five months of sea temperatures around 28°C, the water temperature drops one degree in September, to 27°C, which, again, is still very warm.
With a decrease of only 15 minutes in the course of the month, the length of the days in September is basically constant. The longest day of the month is September 1 with 12.17 hours of daylight; September 30 is the shortest with 12.02 daylight hours. Sunshine is limited to 6 hours per day, the same as the previous four months, as well as October and November. This is due to the fact that September marks the end of the cloudy mini-monsoon or hot season and the start of the very wet and cloudy monsoon season. On average, you can experience sunshine on about half of a typical September day.
And September is cloudy indeed. With an average of 85% of cloud cover, this is about as cloudy as it gets. Historically the cloudiest day of the year is October 5. Cloud cover increases only very slightly throughout the month, from 85% in the beginning to 86% at the end. September 15, a representative day of the month, generally has clear skies 4% of the time, partly cloudy skies 15% of the time and is mostly cloudy 45% of the time. The rest of the time is divided between other less common cloud cover types.
As the start of the monsoon season, September sees an increase of rainfall compared to the previous months, which, by the way, were already fairly wet. September gets a total of 130mm of precipitation and has 11 days of rainfall. The chance of experiencing rainfall on any given day increases in the course of the month. Precipitation is least likely on September 5 with a 51% chance and most likely on September 30 with a 55% chance. The most common types of rainfall, in this order, are light rain, thunderstorms and moderate rain. September has by far the lowest amount of fog days in the year: only two. The average humidity ranges around 80%.
Koh Samui’s weather changes frequently during the day from rainy to sunny and then back to rainy. Most of the holiday-makers will have filtered out of Koh Samui by September as the holiday season will have ended. However, people can still participate in almost all the activities as all the shops and attractions remain open for the entire year.
OCTOBER – Weather Summary
Falling in the middle of the monsoon season, October is an extremely wet month in Koh Samui. Temperatures are still high, too, as they always are on the island. The average daily temperature in October is 27°C, one degree less than September. The daily high temperature ranges around 30°C and the daily low is about 24°C, both also one degree less than the previous month. Those daily highs and lows decrease slightly in the course of the month. October 1 is the warmest day of the month with highs of 31° and lows of 26°C; October 31 is the coldest with highs of 30°C and lows of 24°C. That average daily low is in fact as cold as it ever gets in the resort, so you could go to worse places! Similar to most tropical seaside resorts, the heat tends to become uncomfortable around noon, and it is best to go sightseeing in the morning and evening, in between rain showers. The water of the Gulf of Thailand also gets one degree colder. The sea temperature is now 27°C, which is exactly the same as the air temperature.
October gets extremely rainy, as one of the monsoon months, with a monthly total of 290mm of rainfall. The month also has no less than 16 days of precipitation, which is the highest number in the year and a full five days more than September. October is the second-wettest month of the year, after November. An average October day has an average chance of 56% that it will rain. There is little variation in that percentage in the course of the month. The day with the highest chance of rainfall in October, but also in the whole year, is October 25 with a 57% chance. Three types of precipitation are observed in October: light rain, moderate rain and thunderstorms. Light rain is the most common and occurs on 46% of all rainy days. Thunderstorms come in second with a 36% chance. Moderate rain is experienced on 17% of the days of rainfall. The number of fog days has increased a lot since last month. There now are five. Another increase is seen in the average humidity, which now ranges around 85%.
Being such a wet month, it comes as no surprise that the amount of cloud cover is also very high in October. Cloud cover ranges around 87% in the course of the month and doesn’t change much. The absolute high is observed on October 5 with 88% of cloud cover. This is also the record high for the entire year.
Besides a lot of rain, there is another consequence of high cloud cover. It greatly restricts the amount of sunshine that reaches the beaches. As such, October only has 6 hours of sunshine per day, a number that hasn’t varied much for five months now. This average of 6 hours is observed from May through November, which is when the mini-monsoon and actual monsoon season happen. The length of the days in October doesn’t change much either. The longest day is October 1 with a total of 12.02 hours of daylight, while October 31 is the shortest with 11.47 daylight hours, a monthly decrease of only 15 minutes.
NOVEMBER – Weather Summary
Koh Samui’s temperature patterns are pretty stable throughout the year. November, one of the coldest months of the year, has an average daily temperature of 27°C, still warm by all accounts. The average daily high temperature in November is 29°C, while the average daily low is 24°C. These temperatures are basically constant throughout the month and comparable to December. In terms of temperature, there is very little variation between November days. The island is warm all year round, but there is also always the opportunity to cool off in the comfortably warm sea. The sea temperature in November is 27°C, exactly the same as the average air temperature.
Just like any other month, November’s days are pretty much equal in length. Because of the resort’s location near the equator, there is very little variation in day lengths throughout the year. This month’s longest day is November 1 with 11.47 hours of daylight. The shortest day is November 30 with 11.36 daylight hours. The average amount of sunshine in November is 6 hours per day, a number that has been the same for more than half a year, since the wetter part of the year started in May.
This means that a little more than half of a typical November day is sunny. The rest of the day is cloudy as November falls in the middle of the monsoon season. The average percentage of cloud cover in the course of the month is 86, which is very high. Even though it does not vary substantially as the month passes, a small decrease can be noticed. November 8 is historically the cloudiest day of the month with 87% of cloud cover. By the end of the month, on November 30, cloud cover is 85%. November is a very cloudy month; on a typical day the skies are clear or mostly clear for only 5% of the time and overcast for 46% of the time.
November is also an extremely wet month. It receives a total amount of rainfall of no less than 430 mm in the course of the month, which is far more than any other month. October is the second-wettest month with 290 mm of precipitation. November also has 15 days of rainfall, one day less than October, but that is probably due to the fact that November is a day shorter. This month is the absolute peak of the monsoon season. However, in the course of the month there already is a visible decrease in the chance of precipitation. The highest chance of rainfall occurs in the beginning of the month at 55%. By November 30 that chance has dropped to 46%. The three most common types of precipitation are light rain, thunderstorms and moderate rain, in that order. Light rain occurs on 42% of all rainy days, thunderstorms on 35% and moderate rain on 22%. November also has five fog days, which is about the yearly average. The average humidity in November ranges around 85%, a percentage that will stay virtually the same until the end of March.
DECEMBER – Weather Summary
December marks the end of the monsoon season and the beginning of the dry season in Koh Samui. This is also the cooler part of the year, although cool has to be taken with a big grain of salt. The average temperature is 27°C, only three degrees less than May, the hottest month of the year. The average daily low temperature in December is 24°C; the average daily high is 29°C, both exactly the same as November. These temperatures don’t seem to change at all in the course of the month. December is the second-coolest month of the year, after January, but 88% of the days are still classified as warm and 12% as hot. The temperature of the water in the Gulf of Thailand ranges around 27°C, allowing for a very pleasant dip in the sea.
As the weather moves towards the dry season, the skies start to clear. The beginning of December is characterised by 85% of cloud cover, which means mostly cloudy skies, but by the end of the month it has dropped to 78% , partly cloudy skies. Clearing skies, of course, also result in an increase of sunshine. After seven months, from May through November, of only 6 hours of sunshine per day, December sees an increase of sunshine hours. Now, you can enjoy seven hours of sunshine per day.
With the clearing of the skies, the amount of rainfall drops drastically. December receives a total of 150 mm of rainfall, far less than the enormous cloudbursts of October and November, months with respective totals of 290 mm and 430 mm of precipitation. December is the fourth-wettest month of the year, after the monsoon months of October and November, and May. There are still nine days of rainfall in the course of the month, a number that is shared with May, June and July. The chance that you will experience rain varies throughout the month. In the beginning of the month there is a daily chance of 47% that rainfall will occur; by the end of the month that chance has decreased to 37%. The types of rainfall that are observed are light rain, moderate rain and thunderstorms. Light rain is the most common type, with a 47% chance on any rainy day. Moderate rain is second-most common and is experienced on 27% of the days of precipitation. Thunderstorms occur on 24% of the rainy days. The average humidity in December ranges around 85%, which is very humid. It will stay this way until the end of March. In terms of fog, there is a significant rise compared to November. Now, there are eight fog days, three days more than a month ago and one day less than the absolute maximum of nine in January.
The length of the days in December is constant. The difference between the shortest and longest days is a mere two minutes. December 1 is the longest day of the month with 11.36 hours of daylight. December 21 is the shortest day of the month and also of the entire year with 11.34 daylight hours. December 31 still has 11.34 hours of daylight.