Koh Chang sits in the Gulf of Thailand but its rainy season runs on an Andaman-coast calendar — May to October, opposite the Samui archipelago further south. Its mountainous interior also makes it one of Thailand's genuinely wettest islands. Here's what each month means for weather, closures and everyday life.
Koh Chang sits in Trat province on Thailand's eastern Gulf coast, near the Cambodian border — but unlike the Samui archipelago further south, its rainy season is driven by the southwest monsoon, giving it the same calendar as Phuket and Koh Lanta on the Andaman coast: a dry season from November to April (peak season, calm seas) and a wet season from May to October. Its mountainous, forested interior also makes it one of Thailand's wettest islands — widely cited figures put annual rainfall above 3,000mm. December is the driest month (around 20mm); August is cited by some data sets as the single wettest, though June through September are all genuinely heavy. For live rents by area, use the BAANLYY Koh Chang hub.
Temperatures move modestly across the year; rainfall, seas and which businesses are open change far more. Months marked ★ are dry-season favourites.
| Month | Season | Typical temp | Rain & sea | Verdict |
|---|---|---|---|---|
| January | Dry, cooling | 24-32°C | Minimal rain, calm seas | ★ Excellent — dry and comfortable |
| February | Dry | 24-33°C | Little rain, clear skies | ★ Excellent — reliably dry |
| March | Dry, warming | 25-34°C | Dry, warming toward the hot season | ★ Great — still mostly dry |
| April | Hot, dry (ending) | 26-34°C | Hot, mostly dry, Songkran | Good but hot; last dry month |
| May | Rains begin | 25-32°C | Showers increasing, first closures start | Transitional — shoulder month |
| June | Wet, SW monsoon | 24-31°C | Regular rain, more resorts closing | Low season — rain building |
| July | Very wet | 24-30°C | Among the heaviest-rain months of the year | Low season — quiet, wet, cheap |
| August | Very wet, often heaviest | 24-30°C | Cited by some data sets as the single wettest month | Low season — most closures in effect |
| September | Very wet | 24-30°C | Still heavy rain; flash-flood risk peaks | Low season — wettest window continues |
| October | Wet, easing late | 24-31°C | Rain tapering through the month | Improving late — still unsettled |
| November | Reopening | 23-31°C | Rain fading, seas calming | Improving — resorts reopening |
| December | Driest, peak season | 24-31°C | Driest month (~20mm), sunny | ★ Excellent — festive peak season |
Guide figures compiled from long-run climate averages; actual weather and business closures vary year to year.
This is the point that trips up a lot of first-time visitors and relocators comparing Koh Chang to Thailand's other well-known islands.
Most of Thailand's well-known Gulf of Thailand islands — Koh Samui, Koh Phangan, Koh Tao — sit far enough south and east that they're dominated by the northeast monsoon, giving them a late, short rainy season roughly October-December. Koh Chang is different. It sits much further north on the Gulf's eastern shore, close to the Cambodian border, directly in the path of the southwest monsoon that also drives the rainy season on Phuket, Koh Lanta and the rest of the Andaman coast. The result: Koh Chang's wet season runs May-October and its dry season November-April — the Andaman calendar, not the Samui-archipelago one — even though it's technically a Gulf island.
Koh Chang's mountainous, densely forested interior — protected as Mu Ko Chang National Park and rising to a high point of roughly 744 metres at Khao Salak Phet — forces incoming monsoon air upward, wringing out extra rain over the island (an orographic effect). Widely cited climate data puts Koh Chang's annual rainfall above 3,000mm, noticeably higher than flatter islands like Koh Lanta or Koh Samui and more than double what Bangkok receives in an average year. This is a genuine, distinctive feature of the island's weather, not just a general 'Thailand is rainy' point.
Koh Chang's low season has a real, visible impact — both commercially and on the ground.
Like Koh Lanta, Koh Chang has a real commercial low season — a meaningful share of independently run beachside restaurants, bars and smaller guesthouses close outright for some or all of the June-October wet stretch, most commonly around August and September when rain and rough seas are heaviest. This is a genuine operational pattern, not just quieter streets.
The island's larger resorts, its 24-hour Bangkok Hospital branch, the government hospital, pharmacies, 7-Elevens, supermarkets (Big C, Lotus's, Makro Food) and the Ao Thammachat car ferry all keep running year-round — the ferry timetable does not change for the monsoon, so getting to and around the island isn't cut off the way some travellers assume.
If you're moving to or visiting Koh Chang in the June-October window, confirm ahead that a specific restaurant, dive operator or beach bar you found online is actually open, especially away from White Sand Beach. On the upside, this is also when rents and short-term deals are softest, and it's worth reading the dedicated flood-risk guide before choosing an area to settle in for the season.
September carries the island's peak flash-flood and landslide risk — see the full Koh Chang flood-risk guide for documented events and which areas to avoid, and the Koh Chang safety guide for the wider picture.
For the most reliable weather and the widest choice of open restaurants and bars, target November-April, especially December-February. For lower prices, thinner crowds and a genuinely quieter island, the green season (May-October) delivers real value — just confirm ahead that the specific place you want to eat or stay is actually open.
| When | What to pack |
|---|---|
| Year-round | Light, breathable clothing, reef-safe sunscreen, a hat and good sandals — Koh Chang is warm and humid every month. |
| Dry season (Nov-Apr) | Book accommodation and ferry crossings ahead of the November-April peak, especially December-February when the island is busiest and driest. |
| Green season (May-Oct) | Pack a compact rain shell or umbrella and a dry bag for the ferry crossing, check ahead before assuming a specific restaurant or bar is open, and see the flood-risk guide if you're choosing where to base yourself through the wettest months (June-September). |
White Sand Beach, Klong Prao and Kai Bae along the main west-coast strip keep the widest range of shops, clinics, restaurants and the island's 24-hour hospital open year-round, making them the more practical base for a long low-season stay. Bang Bao and areas nearer the national park's mountainous interior lean more seasonal and carry more flash-flood exposure in the wettest months. Explore the trade-offs on the Koh Chang hub, and model seasonal costs with the Koh Chang cost-of-living guide.
November through April is Koh Chang's dry season and the classic best time to visit — calm seas, minimal rain and every business open, with December and January especially popular and driest. The trade-off is peak-season pricing. The May-October green season offers real value and a much quieter island, though be aware many beachside restaurants and bars close during the wettest stretch, typically June through September.
The wet, or 'green', season runs roughly May to October, driven by the southwest monsoon. June through September is the core of the wet season, with widely cited climate data putting either July or August as the single wettest month (data sets differ) and September carrying the island's peak flash-flood risk. December is the driest month, averaging only around 20mm of rain.
Koh Samui, Koh Phangan and Koh Tao sit further south in the Gulf of Thailand and are dominated by the northeast monsoon, giving them a late rainy season around October-December. Koh Chang sits much further north and east, close to Cambodia, directly in the path of the southwest monsoon that also drives Phuket and Koh Lanta's Andaman-coast rainy season. So Koh Chang's wet season runs May-October and its dry season November-April — the opposite timing to the Samui archipelago, despite both being technically Gulf of Thailand islands.
Yes, genuinely. Koh Chang's mountainous, forested interior (part of Mu Ko Chang National Park, rising to roughly 744 metres) forces incoming monsoon air upward and wrings out extra rain, an orographic effect. Widely cited climate figures put Koh Chang's annual rainfall above 3,000mm — noticeably higher than flatter islands like Koh Lanta or Koh Samui, and more than double Bangkok's average. This is also part of why the island carries real flash-flood and landslide risk in the wettest months; see the dedicated flood-risk guide for details.
Yes — this mirrors the pattern on Koh Lanta. A real share of independently run beachside restaurants, bars and small guesthouses close outright for part of the June-October wet season, most commonly around August and September. Larger resorts, the island's hospitals, pharmacies, supermarkets and the Ao Thammachat car ferry all keep running year-round. If you're visiting or relocating in this window, confirm ahead rather than assuming a specific spot is open.
Somewhat. White Sand Beach, Klong Prao and Kai Bae along the main west-coast strip keep the widest range of shops, clinics and restaurants open year-round, while quieter spots and anything near the national-park interior carry more flash-flood and landslide exposure in the wettest months — see the flood-risk guide before committing to an area for a long low-season stay. Monsoon-season rents are typically softer, so relocating in the wet months can save money.
Primary and official sources are cited above. Government rules, fees and procedures in Thailand change over time and vary by office; always confirm current requirements with the relevant authority before relying on them. BAANLYY never takes paid placement in editorial content.
Whether you come for the dry-season high or the green-season value, match the right Koh Chang area and home to how you want to live.
Hero photo by Balazs Simon on Pexels.