| Month | Mean, °C | Mean max, °C | Mean min, °C | Rain, mm | Rain days | Humidity, % |
|---|---|---|---|---|---|---|
| January | 26.8 | 31.9 | 22.2 | 51.1 | 4.9 | 73 |
| February | 27.3 | 32.0 | 22.9 | 81.5 | 7.4 | 77 |
| March | 28.1 | 32.6 | 24.2 | 140.0 | 12.6 | 79 |
| April | 28.6 | 33.3 | 24.7 | 196.0 | 14.9 | 80 |
| May | 28.4 | 32.8 | 24.8 | 419.9 | 21.9 | 83 |
| June | 27.5 | 31.5 | 24.3 | 777.2 | 25.4 | 87 |
| July | 27.1 | 30.7 | 24.0 | 1,024.1 | 26.6 | 87 |
| August | 27.2 | 30.7 | 24.1 | 969.7 | 27.0 | 88 |
| September | 27.0 | 30.9 | 23.8 | 816.4 | 24.8 | 87 |
| October | 27.0 | 31.8 | 23.6 | 337.6 | 21.3 | 85 |
| November | 27.7 | 32.6 | 23.5 | 85.2 | 9.1 | 75 |
| December | 27.1 | 32.2 | 22.6 | 27.8 | 3.5 | 70 |
| Year | 27.5 | 31.9 | 23.7 | 4,926.5 | 199.4 | 81 |
The table above is a climate normal for the Trad station on the mainland: averages over 30 years, not a forecast and not a measurement on Koh Chang. It is the closest guide to Koh Chang’s seasons that TMD publishes. A single year can be drier or wetter.
Why the data comes from the mainland
TMD’s 1991-2020 report has no station on Koh Chang. The two nearest stations are both on the mainland and about the same distance from the island:
| Figure | Trad (48 501) | Chanthaburi (48 480) |
|---|---|---|
| Coordinates | 11°46’ N, 102°53’ E | 12°37’ N, 102°06’ E |
| Distance to the centre of Koh Chang | about 69 km | about 63 km |
| Annual rainfall | 4,926.5 mm | 2,991.6 mm |
| Rain days a year | 199.4 | 168.5 |
| Driest month | December, 27.8 mm | December, 8.4 mm |
| Wettest month | July, 1,024.1 mm | September, 538.3 mm |
Distances are our calculation in a straight line from the station coordinates in the TMD report to the centre of the island on Wikidata (12.104° N, 102.352° E). The report gives coordinates to one minute of arc, so they are accurate to about 2 km.
We use Trad, as our Koh Chang guide does, and show Chanthaburi for comparison. The two stations disagree on the amount of rain by a factor of 1.6, so neither tells you how much falls on the island. They agree on the timing: the driest month is December, and the rain comes from May to October.
What the numbers show at Trad
Temperature barely changes. Monthly means range from 26.8 °C in January to 28.6 °C in April, highs from 30.7 to 33.3 °C. The coolest nights are in January and December, with average lows of 22.2 and 22.6 °C.
Rain sets the seasons. December gets 27.8 mm, January 51.1 mm, February and November 81.5 and 85.2 mm. From March the totals rise every month, and from June to September 777-1,024 mm falls each month, with rain on 25-27 days out of 30. Mind the method: TMD counts a rain day whenever at least 0.1 mm falls, so short showers count too.
Humidity rises with the rain: from 70% in December to 88% in August. The station has no sunshine observations in the report.
Weather by season at Trad
Our grouping of the monthly TMD figures in the table above (Trad station, 1991-2020).
| Period | Months | Mean max, °C | Rain a month, mm | Rain days a month | Humidity, % |
|---|---|---|---|---|---|
| Driest | December-January | 31.9-32.2 | 27.8-51.1 | 3.5-4.9 | 70-73 |
| Drier shoulder | November, February | 32.0-32.6 | 81.5-85.2 | 7.4-9.1 | 75-77 |
| Rain building | March-April | 32.6-33.3 | 140.0-196.0 | 12.6-14.9 | 79-80 |
| Rainy | May, October | 31.8-32.8 | 337.6-419.9 | 21.3-21.9 | 83-85 |
| Peak rain | June-September | 30.7-31.5 | 777.2-1,024.1 | 24.8-27.0 | 87-88 |
The same months across the country: Thailand in November, Thailand in December. Another station on the eastern Gulf coast: Pattaya weather by month.
Today’s forecast and warnings from TMD
The normals show a typical month, not the coming week. For the next seven days use the TMD 7-day forecast, which is given by region. Heavy rain and storm warnings are on the TMD warnings page. Before a sea crossing, also check the ferry operator’s notice.
Method and limits
- Source: Thai Meteorological Department report Climatological Data of Thailand for 30 Year Period (1991-2020), 2023 edition, printed pages 65 (Trad, WMO 48 501) and 64 (Chanthaburi, WMO 48 480). The report is published on a TMD subdomain
- Station: Trad, 11°46’ N, 102°53’ E, 2 m above sea level, on the mainland. The report notes that the station’s name was changed from Khlong Yai
- Proxy: the island has no station in the report, so the figures describe the region’s seasons, not a beach on Koh Chang
- Period: 30 years, 1991-2020, the latest 30-year period for which TMD has published normals
- How we compiled it: figures copied from the report without recalculation. We checked monthly rainfall and rain days against the annual values and found no discrepancies
- Rain day: at least 0.1 mm in 24 hours, counted from 07:00 to 07:00
- What is missing: sunshine hours (no observations at Trad), sea temperature, waves and ferry operation. We found no primary normals for the sea around Koh Chang
- Next update: when TMD publishes new normals or at our April 2027 review
Getting there, the ferry and where to stay: Koh Chang guide.
FAQ
Is this the weather on Koh Chang itself?
No. TMD's 1991-2020 report has no station on the island. Trad is on the mainland, about 69 km from the centre of Koh Chang in a straight line, and the report notes it was previously called Khlong Yai. Use it for the timing of the seasons; the amount of rain on the island can differ.
What is the best month for weather on Koh Chang?
By the Trad normals, December and January: 27.8 and 51.1 mm of rain, 3.5 and 4.9 rain days, humidity 70-73%. November and February come next with 85.2 and 81.5 mm. The nearby Chanthaburi station also has December as its driest month. The normals do not cover waves, sea temperature or ferry operation.
When is the rainy season on Koh Chang?
At Trad, May to October: 337.6 to 1,024.1 mm a month and 21 to 27 rain days. The peak is June to September, with July the wettest at 1,024.1 mm. The Chanthaburi station, the other nearest one, shows the same rainy months.
When is the dry season on Koh Chang?
At Trad, December and January are the driest (27.8 and 51.1 mm), and November and February are close behind (85.2 and 81.5 mm). From March rainfall climbs: 140.0 mm in March, 196.0 mm in April, 419.9 mm in May.
What are the hottest and coolest months?
At Trad the temperature barely changes: monthly means range from 26.8 °C in January to 28.6 °C in April. April also has the highest average high, 33.3 °C. The coolest nights are in January, with an average low of 22.2 °C.
What is the weather like on Koh Chang in November?
At Trad November is the month the rains end: 85.2 mm and 9.1 rain days on average, a quarter of October's 337.6 mm. Highs are 32.6 °C, lows 23.5 °C, humidity 75%. December is drier still.
What is the weather like on Koh Chang in December?
At Trad December is the driest month of the year: 27.8 mm and 3.5 rain days, humidity 70%. The mean is 27.1 °C, with highs of 32.2 °C and lows of 22.6 °C. The report has no sunshine observations for this station.
Why is the rainfall so high?
Trad's 4,926.5 mm a year is the highest annual total of all 87 stations in the TMD 1991-2020 report. Chanthaburi, at a similar distance from Koh Chang, gets 2,991.6 mm. Neither station measures rain on the island, and the two differ widely, so take the totals as a rough guide.
Sources
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