← Weather & seasons in Thailand
Phuket takes the southwest monsoon from about mid-May to mid-October and the northeast monsoon from about mid-October to mid-February. On the thirty-year normal, February is driest (24.0 mm) and September is wettest (350.4 mm) — a fourteen-fold difference. Similan and Surin national parks close 15 May to 15 October for the 2026 season. April is hottest by daily-maximum mean at 34.4°C; October is coolest by daily-minimum mean at 24.9°C.
The monthly rainfall, measured
Every figure below is a 1991–2020 normal for WMO station 48564 (Phuket), from Thailand’s own submission to the World Meteorological Organization, archived by NOAA. It is a thirty-year average, not a forecast for any single year — but it is measured, not modelled, and it is the same standard the rest of this site uses for city climate comparisons.
| Month | Rainfall normal | What that means here |
|---|---|---|
| Jan | 49.9 mm | Dry season. Coolest, calmest window of the year. |
| Feb | 24 mm | Driest month on record. Best month for diving visibility on the west coast reefs. |
| Mar | 80.7 mm | Still dry; heat starts building toward the April peak. |
| Apr | 135.1 mm | Hottest month by daily-maximum mean (34.4°C). Rain still low but starting to climb. |
| May | 236.9 mm | Southwest monsoon arrives. Rain and humidity rise fast; Similan and Surin close on the 15th. |
| Jun | 249.4 mm | Full monsoon. Showers most days, often short and heavy rather than all-day. |
| Jul | 240.2 mm | Monsoon continues. A brief mid-monsoon lull ("Thai low season") is often reported locally but is not something the normals data isolates. |
| Aug | 308.7 mm | Rain climbing toward the September peak. |
| Sep | 350.4 mm | Wettest month on record — more than fourteen times February's total. |
| Oct | 336 mm | Second-wettest month. Still inside the closure window for Similan and Surin. |
| Nov | 178.2 mm | Monsoon breaking up. Rain drops by nearly half from October. |
| Dec | 82 mm | Northeast monsoon settled in. Dry, clear, and the start of the busiest tourist months. |
The “what that means here” column is our own reading of the measured figure against the published monsoon calendar, not a separate data source.
Two numbers do the most work in this table. February at 24.0 mm is not just Phuket’s driest month — across the twelve Thai stations this site has checked against the same normals, it is one of the driest readings anywhere in the country outside the far inland north. September at 350.4 mm is Phuket’s wettest and among the wettest of any Thai coastal station in this dataset.
Temperature: what we can and can't confirm
The same 1991–2020 normals give two firm temperature points for Phuket: March is hottest by mean daily maximum, at 34.4°C, and October is coolest by mean daily minimum, at 24.9°C. Phuket does not run a wide temperature range across the year the way inland cities do — the sea keeps it within a narrower band, hot and humid essentially year-round with the driest months (December–February) feeling more comfortable because humidity, not temperature, drops.
What this page does not have. A full twelve-month temperature series for Phuket — only the hottest and coolest months from the same normals archive. The archive that would supply the other ten months could not be reached from this run; rather than estimate the missing months, this page states only the two points we can source.
What actually closes, and when
If a Similan or Surin trip is part of the plan, this is the one date range that overrides everything else on this page. The Department of National Parks’ Protected Area Regional Office 5 closes Mu Ko Similan and Mu Ko Surin national parks from 15 May to 15 October 2026, a five-month window timed to the southwest monsoon. The department’s stated reasons are sea safety as the monsoon sets in and time for the reef, coral and beaches to recover before the next season — not a tourism-management decision, a conservation and safety one. Both parks are reached by boat from Phuket and Khao Lak piers, so the closure affects Phuket-based trip planning even though the islands themselves sit in Phang Nga province.
We did not find an equivalent published closure for any dive site or beach on Phuket island itself. Phuket is inhabited and functions year-round; the monsoon changes conditions, it does not close the island.
What we could not confirm
- A full monthly temperature series. Only the hottest and coolest months are sourced; the other ten are not stated rather than estimated.
- Red-flag beach warning dates or the issuing authority. Widely reported to operate on Phuket’s west-coast beaches during the rougher months, but no official source we could open states the criteria or an enforcement record.
- Rain-hours-per-day within the wet season. The monthly totals are measured; how that rain is distributed across each day is not in this dataset.
- Any official cyclone or tropical-storm risk statement specific to Phuket. None was found from the Thai Meteorological Department for this page.
Frequently asked questions
By the numbers, February. It is the driest month in the thirty-year normal — 24.0 mm against a September peak of 350.4 mm — and it falls inside the northeast monsoon window that the Thai Meteorological Department places from roughly mid-October to mid-February, when the government's own description is clear skies, cool air and dry conditions. December and January are close behind. The trade-off is that these are also the most crowded and expensive months, because everyone else has read the same normals.
September, on the numbers: 350.4 mm on average, the wettest month Phuket records, with October close behind at 336.0 mm. What the monthly total does not tell you is the shape of the rain. Locally, and in general Thai Meteorological Department guidance on the southwest monsoon, the pattern in this window tends to be built from shorter, heavier downpours rather than continuous all-day rain — but we have not found an official source that quantifies rain-hours-per-day for Phuket specifically, so treat that as orientation, not a number to plan around.
The clearest, most concrete closure is Mu Ko Similan and Mu Ko Surin national parks — the two marine parks most day trips and liveaboards out of Phuket are built around. The Department of National Parks' Protected Area Regional Office 5 closes both for the 2026 season from 15 May to 15 October, a five-month window timed to the southwest monsoon, stated as both a sea-safety measure and time for the reef and beaches to recover before the next season. Phuket itself does not close — people live here year-round — but if a trip to Similan or Surin is part of the plan, that five-month window rules it out entirely.
Yes, and it is the single most useful fact for anyone choosing between a west-coast island like Phuket and a Gulf island like Koh Samui. Phuket's wettest month is September (350.4 mm); Koh Samui's September normal is a comparatively mild 117.5 mm. Two months later the position flips — Koh Samui's November normal of 444.6 mm is higher than any month Phuket records, while Phuket by November is down to 178.2 mm. See the Best Time to Visit Koh Samui guide on this site for the Gulf-side numbers laid out the same way.
We are not able to give a confirmed, sourced answer to this on a month-by-month basis. Municipal red-flag warning systems on Phuket's west-coast beaches are widely reported to operate during the rougher months, but we could not confirm the issuing authority, the criteria for raising a flag, or an enforcement record from an official source we could open, so no claim about flag dates or swim safety appears on this page. Treat any red flag on any beach as a genuine no-swim instruction regardless of the season, and check conditions locally before entering the water in May through October.
Related guides
- Best time to visit Koh Samui — the Gulf coast, and its opposite wet season.
- Compare Thai cities — the same normals for twelve stations, side by side.
- National parks in Thailand — the fee bands and the law behind park closures.
- Weather & seasons in Thailand — the country-wide picture this page zooms in on.
- Phuket — the city guide.
- Explore Thailand — the section this guide sits in.
Timed your visit. Now time the move.
If Phuket is more than a trip, see what is actually listed here before the next monsoon window closes your travel dates.
Sources & References
- WMO Climatological Standard Normals 1991–2020 — Thailand station data sheets (NCEI Accession 0253808), Phuket station 48564: monthly precipitation totals, annual rainfall of 2,271.5 mm over 145.9 rain days, hottest month March at a 34.4°C daily-maximum mean, coolest month October at a 24.9°C daily-minimum mean
- Thailand government portal, citing the Thai Meteorological Department — the southwest monsoon covers Thailand from about mid-May to mid-October, bringing humid air and general cloud and rain; the northeast monsoon runs from about mid-October to mid-February, bringing clear skies, cool air and dry conditions
- The Nation (Thailand) — the Department of National Parks, Wildlife and Plant Conservation's Protected Area Regional Office 5 announcement that Mu Ko Similan and Mu Ko Surin national parks close for the 2026 monsoon season from 15 May to 15 October, citing sea safety as the southwest monsoon arrives and time for the reef and beaches to recover before the next season
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.
