Short answer. Phuket’s monsoon season runs from May to October, when the south-west wind brings rain and swell to the west coast. The numbers are less dramatic than the word: eleven years of climate normals put the wettest month, May, at 340 mm of rain on 28 days, but only 4 of those are heavy-rain days, and the month still has 286 h of sunshine. What changes most is the sea: 13 rough-sea days in a normal July against 0 in January, and red flags on the west-coast beaches on the rough days. The island does not empty — 1,139,408 visitors came in July 2025, and July is the peak month for Chinese guests — but the Similan Islands close (mid-May to mid-October), boat trips are cancelled on rough days, and hotels discount. How much they discount is a question this index will answer with its own history: the first observation is September 2026, a low-season month, and the high-season revisions will be measured against it.
The two monsoons
Phuket has two monsoons, and only one of them is “the” monsoon season. From November to March the north-east monsoon blows across the Gulf of Thailand and reaches the Andaman coast dry; the sea on the west coast is flat, the sky is clear, and this is the high season. From May to September the south-west monsoon blows in off the Indian Ocean, wet and with a fetch of a thousand kilometres to build a swell; this is the green season, the low season, the rainy season, depending on who is selling what. April and October are the transitions: April hot and increasingly humid, October the wettest month but with a sea already calming.
The climate normals used on this site come from the Open-Meteo ERA5 reanalysis for the west-coast grid point, one value per month from 2015 to 2025, and the figure quoted for each month is the median of those eleven years — the middle year, not the average pulled up by one bad one. Wave and rough-sea fields start in 2022, so they carry a smaller sample. Everything below is from those normals; nothing is a rule of thumb.
Month by month
| Month | Rain | Rain days | Heavy-rain days | Sunshine | Day max | Sea state | Rough-sea days |
|---|---|---|---|---|---|---|---|
| April | 183 mm | 25 | 2 | 311 h | 30.7 °C | calm | 0 |
| May | 343 mm | 28 | 4 | 298 h | 29.8 °C | swell | 4 |
| June | 275 mm | 22 | 4 | 284 h | 29.3 °C | swell | 8 |
| July | 241 mm | 24 | 3 | 279 h | 29.2 °C | rough | 13 |
| August | 270 mm | 25 | 3 | 277 h | 28.9 °C | rough | 9 |
| September | 309 mm | 25 | 6 | 248 h | 28.7 °C | rough | 12 |
| October | 340 mm | 28 | 4 | 286 h | 29.0 °C | calm | 2 |
| November | 270 mm | 27 | 3 | 260 h | 28.7 °C | calm | 0 |
| For contrast: February | 21 mm | 7 | 0 | 312 h | 30.7 °C | calm | 0 |
Rain days count any day with measurable precipitation in the reanalysis, so they run higher than the rainy days a visitor would count; heavy-rain days are the ones that spoil plans. Rough-sea days are days whose modelled maximum wave height exceeds the swimming-safety threshold used by the site’s climate pipeline; the sea-state label is derived from them (calm ≤ 2 days, swell ≤ 8, rough above). The full twelve months, the last year against the normals, and the derivation are on the best-time page.
May
The switch. Rain jumps from April’s 183 mm to 343 mm, the first swell arrives, and the sea goes from calm to swell with 4 rough-sea days in a normal year. Daytime highs ease to 29.8 °C from April’s heat. Mid-May the Similan and Surin national parks close for the season. Hotels post their low-season rates. Indian school holidays put Indian families on the beaches; the sea flags are new to most of them.
June
Drier than May at 275 mm but rougher: 8 rough-sea days and a swell sea. Sunshine 284 h in the month. The quietest month for foreign arrivals in most years — 1,046,614 visitors in June 2025, the lowest figure of that year — and the month when Kata’s surf school has waves.
July
The peak of the swell: 13 rough-sea days, a wave-height normal of 1.5 m, and 241 mm of rain. Yet July is not a quiet month on the island. It is the peak month for Chinese guest arrivals (150,214 in July 2025) and, with the European and Middle Eastern summer holidays, the monthly visitor count climbs back to 1,139,408. Hotel occupancy in the province was 70.7% in July 2025. Patong, Kata and Karon in July feel like a season; the north-west beaches do not.
August
Much like July: 270 mm of rain, 9 rough-sea days, 277 h of sunshine. Foreign guest arrivals in the province were 816,981 in August 2025. The Bang Tao and Kamala beach fronts are quiet; the east coast and Phuket Town are not affected at all, because the swell is a west-coast fact.
September
The month this index was born in, and statistically the wettest of the true monsoon months after October: 309 mm on 25 days, 6 heavy-rain days (the highest normal of any month), the lowest sunshine of the year at 248 h, and 12 rough-sea days. September and early October are when the tropical depressions that give the season its reputation tend to cross; a flooded road in Patong or Chalong is a September story. It is also the cheapest month to fly from most of the index’s ten countries and the month with the fewest airport passengers in the recent series (September 2025 (1.02 M)).
October
Wettest month by rainfall — 340 mm on 28 days — but the wind has dropped and the sea is already calm, with only 2 rough-sea days in a normal year against September’s 12. The rain comes in heavy afternoon bursts between long clear mornings. The Similan Islands reopen in the middle of the month, the Vegetarian Festival fills Phuket Town’s streets for nine days, and hotels start moving to shoulder rates. October is the month residents recommend to friends who want the low-season prices with a swimmable sea.
November
The transition completes: 270 mm of rain, still 27 rain days, but a calm sea with 0 rough-sea days and the high season’s calendar under way from the first week. Russian, British and French arrivals peak from November — the arrivals page shows every market by month — and hotel rates step up.
The flags, and why they matter more than the rain
The beach-flag system on the west coast is simple and taken seriously by the lifeguards who run it: green for safe, yellow for caution, red for no swimming. From May to October the red flags are on the beaches with the strongest rip currents — Patong, Karon, Kata, Surin, Nai Harn on the worst days — for stretches of days at a time. Rip currents are the mechanism: the swell dumps water on the beach, the water finds a channel back out, and a swimmer standing chest-deep is carried out faster than anyone can swim against. The escape is sideways, along the beach, not towards the shore; the mistake is fighting the current until exhausted.
Every year people drown on Phuket’s beaches in the monsoon, and every year most of them are visitors swimming on red-flag days. The numbers in the table — 13 rough-sea days in July, 12 in September — are the number of days a normal month has when the flags are likely to be red on the exposed beaches. A green-flag day in July is a fine swimming day; a red-flag day in July is not, whatever the sky looks like.
The water itself is never the problem. The sea off the west coast has a normal of 29.9 °C in July and 29.2 °C in September, against 31.0 °C in May and 28.8 °C in January (Open-Meteo marine data, monthly normals since 2022); the warmest month of the year is May, the coolest January, and the whole year sits inside a band of about two degrees. The health risk that does follow the rain is dengue: Phuket reported 1,546 cases in 2025, 67% of them between May and October, with the peak in July — the Aedes mosquito bites by day around houses and gardens, so repellent at dawn and dusk and no standing water on the terrace matter more in these months than at the beach. Both series, with the air-quality monitor in Phuket Town, are on the environment page.
Where to swim in the monsoon: the sheltered and east-facing water. Panwa’s Ao Yon, the beaches reached by longtail from Rawai’s pier, the northern corner of Bang Tao bay under Layan’s headland on moderate days, Nai Harn on calmer days, and the resort pools. The area guide notes which areas are sheltered; the Panwa and Phuket Town profiles make the case for the east in these months.
What closes and what changes
- Similan and Surin islands: closed by the Department of National Parks for the whole monsoon, mid-May to mid-October. In 2026 the Similans closed on 15 May with reopening scheduled for mid-October, the exact day published a week or two ahead. No boats, no exceptions. The index prices the Similan day at $76 per adult and tags it
highseason whatever month it was measured, because it only exists in the open season. - Phi Phi, Phang Nga Bay, Coral Island, Racha: open all year, cancelled on rough days by the harbour master. Speedboats to Phi Phi in July and August are the trips most often cancelled or turned into long, wet crossings; Phang Nga Bay, on the sheltered eastern side, is the boat day that almost always runs. Prices per adult in the September 2026 revision: Phi Phi $63, Coral Island $39, Phang Nga (“James Bond”) in the range $35–109 across n = 12 operators.
- Beach clubs and beachfront restaurants on the west coast trim hours or close for a few weeks, mostly in September.
- Dengue: mosquito-borne dengue rises with the rain, and the wet months are the months when a fever that lasts into a third day should be seen by a doctor rather than waited out. The island’s hospitals catalogue lists which hospitals run a 24-hour emergency room, which languages they speak and what a dengue NS1 test cost when it was last checked; the nationwide medical emergency number is 1669.
- Flights: fewer nonstop frequencies from Europe and some Indian cities between June and September; the country hubs track routes by season.
- The rest: Big Buddha, Old Town, the elephant sanctuaries, the markets, the Muay Thai camps, the diving on the east side and at Racha — unchanged. The elephant sanctuary half-day is $88 and the Big Buddha and Old Town half-day $26 in the current revision, and both are better in a rain shower than a boat is.
Who comes in the monsoon
The idea that Phuket empties from May to October is a European idea. The Ministry of Tourism and Sports counted 14.25 M visitors in Phuket in 2025, and the monthly series shows the low season as a dip, not a collapse: 1,330,782 in January 2025, 1,046,614 in June, 1,139,408 in July. Provincial hotel occupancy was 86.4% in January 2025 and 66.8% in June — lower, and still a majority of rooms.
The markets swap. Russian arrivals peak in January and bottom out in October; British in November and March; Australians in January and September. Chinese arrivals peak in July — the summer holidays — and Indian families fill May and June before their own monsoon. The Middle East’s summer sends visitors who find 29.2 °C and rain a relief. So the west-coast towns in July have a different crowd rather than a smaller one, and Bang Tao, Layan and the resort beaches of the north are where the low season is actually low. The statistics hub has the full picture by year, month and nationality, and the statistics guide explains it.
Prices in the monsoon: what the index can say today
Every guide to Phuket says the low season is cheaper, and every one of them quotes a percentage from somewhere. This one does not, yet. The index’s first observation is September 2026 — a low-season month. Every price point carries a season tag (high, low, shoulder or all) and an observation month, and the history file takes a point per month from here on. When the 1 November revision is measured, the high-season medians will be set beside these low-season ones, area by area and class by class, and the gap will be reported as a measurement with sample sizes on both sides. Until then the honest statement is: the current low-season medians are these.
| Series (low season, September 2026) | Median | Range | n |
|---|---|---|---|
| Hotel, four-star, island-wide, per night | $62 | $41–134 | 210 |
| Hotel, four-star, Patong | $42 | $25–74 | 10 |
| Hotel, four-star, Bang Tao | $81 | $53–178 | 22 |
| Hotel, five-star, island-wide | $141 | $71–219 | 87 |
| Villa, three-bedroom, island-wide, per month | $3,975 | $2,728–4,783 | 125 |
| A mid-range day, Patong, per person | $39 | $26–55 | 12 |
What is structural and can be said now: hotel rates follow the season; the daily basket — street food, scooter, massage — almost does not, because it is priced for residents; airport transfers are fixed tariffs; villa owners in the north-west, who ask three-month minimums from December, are flexible about a month in the wet season, which the villa guide discusses. So the saving is the room, and the room is the largest line in a week, which the week-budget guide adds up.
A monsoon week that works
Arrive in late September or October rather than July if the sea matters; arrive in July if the crowd does not. Stay on the east side or in Phuket Town for the food and the sheltered water, or in Kata for the surf, rather than on an exposed north-west beach you cannot swim from. Book the Phang Nga Bay boat, not the Phi Phi speedboat, for the day that must not be cancelled. Keep the mornings for the beach and the afternoons for the Old Town, the sanctuaries and the massages; the rain normals are afternoon and overnight rain. Watch the flags every single day, because the sea does not care that it is sunny. And read the month table rather than a brochure: 340 mm of rain sounds like a lot until you see that it falls on 4 heavy days out of thirty-one, and that 286 h of sunshine is more than a European summer month manages.
FAQ
When is the monsoon season in Phuket?
The south-west monsoon runs from May to October. In the climate normals (2015–2025) the wettest month is May at 340 mm of rain; May brings 343 mm, September 309 mm. The roughest sea is in July, with a normal of 13 rough-sea days on the west coast; the sea is back to calm by November.
Does it rain all day in Phuket during the monsoon?
Rarely. A normal monsoon month has 22–28 days with some measurable rain but only 3–6 heavy-rain days (6 in September, 4 in June); most rain falls in afternoon or overnight bursts, and even September keeps 248 h of sunshine in the month. All-day rain happens a handful of times a season, usually when a tropical depression crosses the Andaman.
Can you swim in Phuket in the low season?
On green-flag days and at sheltered beaches, yes; on red-flag days, no. The west coast has rip currents from May to October — the normals show 8 rough-sea days in June and 12 in September — and drownings happen every year among people who ignore the flags. East-facing and sheltered bays (Panwa, Rawai’s islands by boat, Nai Harn on calmer days, Bang Tao’s northern end) are the low-season swimming.
Are the Similan Islands open in the monsoon?
No. Mu Ko Similan National Park closes for the south-west monsoon every year from mid-May to mid-October — in 2026 the park closed on 15 May and is due to reopen in mid-October, the exact date announced by the Department of National Parks a week or two ahead. Similan day trips are priced by the index for the open season only, at $76 per adult.
How much cheaper is Phuket in the monsoon season?
Hotels discount, but this index will not quote a percentage it has not measured. Its first observation is September 2026, a low-season month, and every price point carries a season tag; the high-season revisions from November will be set against these to report the real gap, area by area. The current low-season medians are on the index pages: $62 for a four-star night island-wide.
How many tourists visit Phuket in July or August?
More than most people expect. The Ministry of Tourism and Sports counted 1,139,408 visitors in Phuket in July 2025 and 1,046,614 in June, against 1,330,782 in January 2025. July is the peak month for Chinese guest arrivals (150,214 in July 2025), which is why the low season is not quiet in Patong and Kata.