September · Thailand weather
Thailand in September: Weather, What to Expect & Where to Go
Updated
September is Thailand's wettest month. Bangkok and the Andaman coast get the worst of it; even the Gulf starts to dampen by month-end. If you're not tied to school holidays, it's the cheapest month to visit — but plan around weather, not the other way around.
Best region
Gulf
Still the driest region — Samui's wet season hasn't fully started.
Avoid
Andaman
Phuket and Krabi see their wettest month of the year. Flooding is common in low-lying areas.
Wet-season peak
September is the wettest month nationwide. Flights and hotels are at their cheapest, but plan around rain — not the other way around.
September weather, region by region
Average temperatures and rainfall across Thailand's five climate regions in September. Tap the climate map on the homepage for an interactive month-by-month view.
| Region | Avg temp | Rainfall | Visit rating |
|---|---|---|---|
North Chiang Mai | 27°C | 220mm | Good |
Northeast Nakhon Ratchasima (Korat) | 28°C | 230mm | Good |
Central Bangkok | 29°C | 320mm | Mixed |
Andaman Phuket | 28°C | 400mm | Good |
Gulf Koh Samui | 28°C | 170mm | Great |
City spotlights
One city per region — what September actually feels like on the ground, and what to do or skip.
North
Chiang Mai
By the numbers
Chiang Mai averages 27°C — highs around 30°C, nights around 22°C. Around 220mm of rain across 18 days. Wettest month of the year in the north.
Wet, but mountain views between storms are stunning. Cheap, quiet, and atmospheric.
Wet, but mountain views between storms are stunning. Cheap, quiet, and atmospheric — bring waterproofs.
Year-round climate
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Northeast
Nakhon Ratchasima (Korat)
By the numbers
Korat averages 28°C with around 230mm of rain across 19 days. Khao Yai's waterfalls peak; trails turn to mud.
Heaviest rain of the year in Isaan. Waterfalls thunder but long hikes need guides.
Heaviest rain of the year for Isaan. Khao Yai's waterfalls are at peak power but trails turn to mud — go with a guide or skip the long hikes.
Year-round climate
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Central
Bangkok
By the numbers
Bangkok averages 29°C with around 320mm of rain across 22 days. Wettest month of the year. Flash flooding shuts roads regularly.
Highest monthly rainfall of the year. Skip if you want predictable sightseeing.
Highest monthly rainfall of the year. Flash flooding shuts roads regularly — skip if you want predictable sightseeing.
Year-round climate
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Andaman
Phuket
By the numbers
Phuket averages 28°C with around 400mm of rain across 24 days. Wettest month of the year. Most beach activities suspended.
Wettest month of the year. Long-tail boats stay docked, dive operators are closed, beaches see rough surf.
Wettest month of the year. Long-tail boats stay docked, dive operators are closed, beaches see rough surf.
Year-round climate
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Gulf
Koh Samui
By the numbers
Koh Samui averages 28°C with around 170mm of rain across 11 days. Sea temperature 29°C. Still relatively dry.
Best beach option in September. Worth combining with the Phuket Vegetarian Festival as a day trip.
Still relatively dry — your best beach option in September. Worth combining with the Phuket Vegetarian Festival as a day trip.
Year-round climate
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Events & festivals in September
Vegetarian Festival (Phuket)
Nine-day Taoist festival, dates shift annually but usually fall in late September or early October. Phuket Town is the centre — vegetarian food everywhere, plus street processions with body-piercing rituals.
Where to actually go
Ten days in September
- 4days
Bangkok
Wettest month of the year. Lean into museums, malls, cooking classes.
Train · 13h overnight sleeperBook on 12Go - 3days
Chiang Mai
Wet but quiet and cheap. Mountain views between storms are stunning.
Flight · ~3h with layoverBook on 12Go - 3days
Koh Samui
Still relatively dry. Best beach option in September.
Skip the Andaman coast in September. Phuket and Krabi see their wettest month — beach activities largely suspended. If you must visit for the Vegetarian Festival, do it as a 2-night detour from Samui.
Sea conditions in September
Thailand has two coastlines on opposite monsoon calendars. Here's what each looks like this month for swimming, diving, and boat trips.
Andaman coast — Phuket, Krabi, Phi Phi
Worst month of the year. Long-tail boats grounded, dive operators closed, west-facing beaches dangerous due to surf. Wait for late October.
Gulf coast — Samui, Phangan, Tao
Still good. Sea temperature 29°C, calm seas, Koh Tao diving visibility 20–25m. Ferries on schedule.
How crowded is Thailand in September?
Cheapest month of the year. Flights and hotels at their annual lows everywhere. The only event drawing crowds is the Phuket Vegetarian Festival (usually late Sep/early Oct), which fills hotels in Phuket Town.
What to pack for Thailand in September
- Genuinely waterproof rain jacket (not a thin poncho)
- Quick-dry clothes only
- Waterproof or sacrificial shoes
- Strong insect repellent
- Dry bag for electronics — non-negotiable in September
September is the wettest month of the year. Don't pretend otherwise. Plan around weather, accept rain days, and bring genuinely waterproof gear — not the dollar-store ponchos sold at 7-Eleven.
Thailand in September — common questions
Is September a good time to visit Thailand?
It's the cheapest month and the wettest. Worth it for experienced travellers or culture-focused trips; not worth it for first-time visitors who want a guaranteed-sun beach holiday. Bangkok, Phuket, and Krabi see their wettest month of the year; the Gulf islands and the north stay manageable.
Is September rainy season in Thailand?
Yes — September is the wettest month of the year across most of the country. Bangkok sees around 320mm of rain across 22 days; Phuket sees 400mm across 24 days. Only the Gulf coast (Samui, Phangan) stays relatively dry.
How wet is Bangkok in September?
Bangkok averages around 320mm of rainfall across 22 wet days in September — its rainiest month. Daily afternoon storms are routine, and flash flooding in low-lying neighbourhoods (Asok, parts of Sukhumvit, parts of the Old Town) shuts roads regularly. Plan around it, don't fight it.
What's the Phuket Vegetarian Festival?
A nine-day Taoist festival celebrated by Phuket's Thai-Chinese community, usually falling in late September or early October. Vegetarian food (no meat, no garlic, no onions) is served across Phuket Town, and street processions feature body-piercing rituals — devotees walk through the streets with skewers through their cheeks. Genuinely unusual, and underrated as a cultural experience.
Is September a good time for Koh Samui?
Yes, relative to the rest of Thailand. Koh Samui sees around 170mm of rain across 11 days in September — meaningful but manageable. Sea temperatures stay at 29°C, ferries run on schedule, and diving on Koh Tao remains excellent. It's the best beach option in the country this month.
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Gulf islands, cultural Bangkok
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Thailand in October
Andaman returning to form, end-of-Lent festivals
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