Short answer
September is the wettest month in Phuket: the Thai Meteorological Department's 1981–2010 normals give 361.2 mm of rain over 22.1 rainy days, with the lowest mean daily maximum of the year, 31.5 °C. The west-coast sea is rough, with red flags at the main beaches, Maya Bay stays closed until 30 September, and the Similan Islands are closed until mid-October. Boat days still run when the sea allows, hotels are at their cheapest, and Phang Nga Bay is the sheltered option.
September is the wettest month of the year
No month in Phuket has more rain. The Thai Meteorological Department's 1981–2010 normals for the Phuket station give 361.2 mm over 22.1 rainy days for September, against 286.8 mm in August, and a mean daily maximum of 31.5 °C, the lowest of the year, with a mean minimum of 24.6 °C. The airport station in the north records 399.1 mm over 22.8 days. The newer 1991–2020 table on Wikipedia's Phuket City page gives 350.4 mm and 18.9 days with 1 mm or more.
The Thai weather service's climate summary says rainfall on the west coast of southern Thailand peaks in September, and that the Inter Tropical Convergence Zone, a belt of converging winds and heavy rain, lies over central Thailand in September and over the south in October. Humidity is 82 percent and sunshine is down to 108 hours in the month, about 3.6 hours a day, the lowest of the year, in the Royal Irrigation Department's figures on Wikipedia's Phuket Province page. The wettest single September day in the table is 172.8 mm.
Waves, flags and what the park measured this year
The west coast takes the monsoon waves. Phuket 101 says the Andaman Sea has wave heights of 2 to 3 metres in September, leading to red flags at Patong, Kata, Karon and Surin because of strong currents, and that east-coast beaches such as Panwa and Ao Yon, sheltered from the swell, are the safer swim. It rates the month as rough with strong currents and tells swimmers to respect the red flags, and to use the hotel pool when they are up.
The water itself is warm. In its monthly survey of Maya Bay during the closure, the Department of National Parks measured the sea 22 times in September 2026 and found an average temperature of 30.25 °C. The same report counted up to 278 adult blacktip reef sharks near the beach on the morning of 2 September. Warm water is not safe water: the west-coast risk is the current, not the temperature. Our guide to rip currents and red flags explains the flags.
Maya Bay: closed until 30 September, open from 1 October
The national park closes Maya Bay every year from 1 August to 30 September, and the Department of National Parks gave exactly those dates for 2026. Phuket 101 says the beach reopens on 1 October and that the park confirms the exact dates each year, which can shift by a day or two. On our Phi Phi and Maya Bay speedboat tour, from $75 per person, the bay is seen from the boat only until it reopens.
Phuket 101 says the other stops stay open, including Pileh Lagoon and Bamboo Island. If walking onto Maya Bay is the reason you are going, book for 1 October or later. Even then, the Department of National Parks said on 15 October 2026 that the opening of some attractions may change with the weather, for the safety of visitors and staff. Our guide to Phi Phi in August and September covers the closure.
Phang Nga Bay in September: the sheltered option
Phuket 101 calls Phang Nga Bay one of September's best activities, because its limestone cliffs act as a barrier against strong winds and waves, so the sheltered water stays calm enough for boat tours and kayaking when other marine activities are restricted. It adds that the hidden lagoons and sea caves can be explored in peace even in rain, with fewer crowds and lower prices. Our James Bond Island and Phang Nga Bay canoe tour is from $85 per person.
The details we hold list no closed season for this day. It runs about 8.5 hours from Laem Nga pier on Koh Siray, with hotel pickup between about 7:00 and 8:00 am, and includes the national park fee, lunch at Koh Panyee, snorkelling gear and sea canoeing at Hong Island with a professional paddler. Low tide can change the order of the stops. If the sea is unsafe, the operator moves the trip to another date or refunds it, so keep a spare day.
Prices, crowds and the green island
September is the cheapest month on the island, says Phuket 101: hotels are nearly empty, luxury resorts offer big discounts, and it advises asking about upgrades and extras at check-in. The roads are not hectic and all the attractions are open, apart from the Similan Islands. Its advice for a wet day is to book spa treatments early, because everyone in the hotel has the same idea once the rain starts.
The landscape rewards the rain. Phuket 101 says the island is lush and green after months of monsoon, that waterfalls are at their most impressive, and that some Septembers surprise everyone by staying dry. The pattern it describes is sun in the morning, cloud building in the afternoon and heavy rain in the evening, so mornings are the best window for outdoor plans. Our guide to rainy-day things to do in Phuket covers the afternoons.
Festivals around September: Por Tor and the Vegetarian Festival
September overlaps two Hokkien Chinese festivals. Phuket 101 says the Por Tor Hungry Ghost Festival is a month-long tradition in August or September, with offerings at shrines such as Por Tor Gong in Phuket Town, and that in 2026 it ran from 19 August to 6 September. Red turtle-shaped cakes called ang ku are its symbol. The dates follow the lunar calendar and move every year.
The Phuket Vegetarian Festival begins on the first day of the ninth Chinese lunar month, which Wikipedia says usually falls between late September and early October. In 2026 the Tourism Authority of Thailand put it at 10 to 18 October, with street processions in Phuket City from 11 October. Phuket 101 says many restaurants in town close during the festival and the rest serve vegetarian food only. Our Phuket Vegetarian Festival guide explains what to expect.
Who September suits, and what to pack
September suits the cheapest-rooms traveller, the flexible one who can use any dry morning, and anyone who wants a green island and a quiet Old Town. Of our days, the sheltered bay is the easier fit in the wettest month. It does not suit people who want blue-sky photographs, a swim at a west-coast beach, the Similans or Maya Bay itself. Guests over 70, infants under 1 year and pregnant women cannot be taken on our speedboats.
Pack a light raincoat, waterproof sandals, a dry bag for the phone, sunscreen and seasickness tablets, as Phuket 101 advises, plus swimwear and a towel; towels are not included on the boat. For the months either side, read Phuket in August and Phuket in October, and compare the two classic days in our Phi Phi or James Bond Island guide.
Practical checklist
- Book for 1 October or later if you want to walk onto Maya Bay.
- Plan outdoor things for the morning, and keep spa, malls and Old Town for the afternoon.
- Treat red flags as a ban on swimming at that beach; use a pool or an east-coast beach.
- Keep a spare day for any boat trip, since the operator moves or refunds trips when the sea is unsafe.
- Pack a rain layer, a dry bag, sunscreen and seasickness tablets.
Questions and answers
Is September the wettest month in Phuket?
Yes. The Thai Meteorological Department's 1981–2010 normals for the Phuket station give 361.2 mm over 22.1 rainy days in September, the most of any month, against 286.8 mm in August.
Is Maya Bay open in September?
No. The national park closes it from 1 August to 30 September, and the Department of National Parks gave the same dates for 2026. Phuket 101 says it reopens on 1 October. On our Phi Phi tour you see it from the boat only.
Does the James Bond Island tour run in September?
Yes. The details we hold list no closed season, and Phuket 101 says the limestone cliffs keep Phang Nga Bay calm enough for boat tours and kayaking. If the sea is unsafe, the operator moves the trip or refunds it.
Can I swim in the sea in Phuket in September?
Only when the flag allows it. Phuket 101 reports red flags at Patong, Kata, Karon and Surin and safer swimming on the east coast at Panwa and Ao Yon. The water is warm, 30.25 °C at Maya Bay in the park's 2026 survey.
Are the Similan Islands open in September?
No. Phuket 101 says they close from mid-May to mid-October, and our Similan tour runs only from 15 October to 14 May.