What is the sea temperature in Phuket by month?
Between 28.8 °C in January and 31.0 °C in May as a monthly normal (median of 2022–2026, Open-Meteo Marine API at 7.99°N 98.28°E). Every month of the year is above 28 °C; the year-round mean is 29.7 °C.
Phuket sea temperature, air quality and dengue by month
How warm the Andaman Sea is off the west coast in each month, what the PM2.5 monitor in Phuket Town records, and how many dengue cases the province reports each week — three environment series a traveller actually feels, reproduced from open sources, never estimated.
Source: Open-Meteo Marine API, daily sea-surface temperature at 7.99°N 98.28°E, 2022-12–2026-08. Statistics · Best time to visit · All sources
29.9 °C
Sea temperature, August 2026
May · 31.0 °C
Warmest sea (normal)
January · 28.8 °C
Coolest sea (normal)
11.3 µg/m³
PM2.5, August 2026
0 / 62
Days above the Thai 24-h standard
1,546
Dengue cases, 2025
Sea-surface temperature by calendar month, °C (median of 2022–2026)
| Month | Mean, °C | Lowest day | Warmest day | n years |
|---|---|---|---|---|
| January | 28.8 | 28.2 | 29.5 | 3 |
| February | 29.1 | 28.5 | 30.1 | 3 |
| March | 29.8 | 28.6 | 31.1 | 4 |
| April | 30.7 | 28.6 | 32.2 | 4 |
| May | 31.0 | 29.6 | 32.3 | 4 |
| June | 30.1 | 29.3 | 31.8 | 4 |
| July | 29.9 | 29.2 | 31.0 | 4 |
| August | 29.9 | 29.1 | 31.2 | 4 |
| September | 29.2 | 28.4 | 30.3 | 3 |
| October | 29.5 | 28.7 | 30.6 | 3 |
| November | 29.8 | 28.5 | 30.8 | 3 |
| December | 29.0 | 28.2 | 30.0 | 4 |
Mean, °C: median of the monthly means over the years on file; Lowest day / Warmest day: extreme daily values seen in that calendar month, any year. The warmest month is marked. Source: Open-Meteo Marine API, daily sea-surface temperature at 7.99°N 98.28°E, 2022-12–2026-08.
Sea-surface temperature, last 24 months, °C
Mean, °CNormal
| Month | Mean, °C | Lowest day | Warmest day | Normal | Δ |
|---|---|---|---|---|---|
| August 2026 | 29.9 | 29.5 | 30.5 | 29.9 | 0.0 |
| July 2026 | 30.1 | 29.7 | 30.7 | 29.9 | +0.2 |
| June 2026 | 30.0 | 29.3 | 30.7 | 30.1 | -0.1 |
| May 2026 | 31.1 | 29.8 | 32.2 | 31.0 | +0.1 |
| April 2026 | 30.9 | 30.2 | 32.0 | 30.7 | +0.2 |
| March 2026 | 29.6 | 28.6 | 30.7 | 29.8 | -0.2 |
| February 2026 | 29.1 | 28.7 | 29.8 | 29.1 | 0.0 |
| January 2026 | 28.8 | 28.5 | 29.4 | 28.8 | 0.0 |
| December 2025 | 28.9 | 28.5 | 29.3 | 29.0 | -0.1 |
| November 2025 | 28.9 | 28.5 | 29.6 | 29.8 | -0.9 |
| October 2025 | 29.2 | 28.7 | 29.9 | 29.5 | -0.3 |
| September 2025 | 29.0 | 28.6 | 29.5 | 29.2 | -0.2 |
| August 2025 | 29.8 | 29.2 | 30.4 | 29.9 | -0.1 |
| July 2025 | 29.7 | 29.5 | 30.1 | 29.9 | -0.2 |
| June 2025 | 29.8 | 29.3 | 30.4 | 30.1 | -0.3 |
| May 2025 | 30.2 | 29.6 | 31.5 | 31.0 | -0.8 |
| April 2025 | 30.5 | 29.9 | 31.5 | 30.7 | -0.2 |
| March 2025 | 30.0 | 29.3 | 30.6 | 29.8 | +0.2 |
| December 2024 | 29.4 | 29.1 | 30.0 | 29.0 | +0.4 |
| November 2024 | 29.8 | 29.1 | 30.6 | 29.8 | 0.0 |
| October 2024 | 29.8 | 29.1 | 30.5 | 29.5 | +0.3 |
| September 2024 | 29.2 | 28.4 | 30.1 | 29.2 | 0.0 |
| August 2024 | 30.6 | 29.7 | 31.2 | 29.9 | +0.7 |
| July 2024 | 30.4 | 30.0 | 31.0 | 29.9 | +0.5 |
Δ: month minus its normal, °C. Newest first. Source: Open-Meteo Marine API, daily sea-surface temperature at 7.99°N 98.28°E, 2022-12–2026-08.
PM2.5 by month, µg/m³
| Month | Monthly mean | Worst day | Days > 37.5 | Days > 15 | Days measured |
|---|---|---|---|---|---|
| August 2026 | 11.3 | 26.8 | 0 | 6 | 31 |
| July 2026 | 8.7 | 16.2 | 0 | 1 | 31 |
µg/m³; Days > 37.5: daily means above Thailand's 24-hour standard (37.5 µg/m³); Days > 15: above the WHO 2021 guideline (15 µg/m³). Source: Air4Thai, Pollution Control Department — station Municipal Health Center, Talat Yai, Mueang Phuket, hourly PM2.5.
Dengue cases by month, 2025
| Month | Cases | Deaths | Weeks |
|---|---|---|---|
| January 2025 | 152 | 0 | 5 |
| February 2025 | 68 | 0 | 4 |
| March 2025 | 45 | 0 | 4 |
| April 2025 | 100 | 0 | 5 |
| May 2025 | 140 | 0 | 4 |
| June 2025 | 278 | 1 | 4 |
| July 2025 | 280 | 0 | 5 |
| August 2025 | 142 | 0 | 4 |
| September 2025 | 98 | 0 | 4 |
| October 2025 | 101 | 0 | 5 |
| November 2025 | 101 | 0 | 4 |
| December 2025 | 41 | 0 | 5 |
approximation — each epi week counted in the month that contains its Wednesday. The peak month is marked. Source: Department of Disease Control, Ministry of Public Health — dengue situation report, Health Region 11, Phuket province row.
What the sea temperature series measures
The sea-surface temperature on this page is the Open-Meteo Marine API's daily value at 7.99°N 98.28°E, a point in the Andaman Sea a few kilometres off the west coast between Bang Tao and Layan. The marine archive carries the variable for this point from 2022-11-24, so the first complete month is December 2022 and the file runs to August 2026 — 43 complete months over 2022–2026. Each month stores three numbers: the mean of the daily means, the lowest daily minimum and the highest daily maximum. A month is written only when every day has a value; January 2025 and February 2025 are missing from the archive and stay empty here rather than being filled from neighbours. The normals table is the median of the monthly means over the 4 years on file for each calendar month — a short record compared with the eleven-year land climate normals on the best-time page, and the n column says so for every row.
The Open-Meteo marine product is a model reanalysis of the open sea, not a thermometer on the beach: water inside a shallow bay at noon in April is warmer than the number, the water at the reef after a monsoon upwelling can be cooler. What the series is good for is the shape of the year and the month-to-month comparison, which is stable from year to year, and the honest answer to the question every visitor asks — whether the sea is warm enough to swim in — which for Phuket is yes in every month: the coolest normal on file is 28.8 °C in January and the warmest 31.0 °C in May, a span of 2.2 degrees around a year-round mean of 29.7 °C.
Warmest and coolest sea: May against January
The Andaman off Phuket is warmest at the end of the dry season, when the north-east monsoon has died and the south-west monsoon has not yet stirred the water: May at 31.0 °C, with 8 of the twelve normals at or above 29.5 °C. The single warmest month on record is May 2024 at 31.8 °C; the highest daily maximum in any May on file is 32.3 °C. Those are coral-bleaching temperatures — the 2024 bleaching event on Phuket's reefs coincided with exactly this kind of April–May peak — and the reason the snorkelling trips to Racha and Coral Island are best in the cooler, clearer months rather than in the hottest ones.
The coolest sea comes with the monsoon swell and the mixing it brings: January at 28.8 °C, and the lowest single month on record is January 2023 at 28.6 °C. Even that is warmer than a Mediterranean August, which is the point of the comparison for visitors from Europe: there is no month in which the sea temperature argues against a swim; the argument in the green season is the flags on the beach and the rough-sea days on the best-time page, not the temperature. The last-24-months table shows how each month compared with its normal; a monsoon month that runs warm usually means a weak swell and a calmer sea than usual.
Air quality: what the PM2.5 monitor in Phuket Town records
PM2.5 is fine particulate matter — the pollutant behind the haze seasons of Chiang Mai and Bangkok — and the question travellers ask about Thailand is whether Phuket has one. The station used here is the Pollution Control Department's reference monitor 43t at the Municipal Health Center in Talat Yai, Phuket Town, which is published on the Air4Thai network; the page stores one line per month from its hourly readings: the mean of the daily means, the worst single day, and the number of days above 37.5 µg/m³ (Thailand's 24-hour standard) and above 15 µg/m³ (the WHO 2021 guideline). A day needs at least 18 valid hours to count and a month at least 24 days.
The latest month on file, August 2026, averaged 11.3 µg/m³ with a worst day of 26.8 µg/m³, 0 days above the Thai standard and 6 above the WHO guideline. Across the 2 months recorded (July 2026 to August 2026) the mean is 10.0 µg/m³ and 0 of 62 measured days exceeded 37.5 µg/m³. The Air4Thai history service serves only the most recent weeks, so this series began with the site's first collection and grows by one month every refresh; the months that matter most for the haze question — February to April, when smoke from field burning on the mainland and in Sumatra occasionally reaches the island — will appear here as they are recorded, and nothing before July 2026 is claimed.
Dengue: 1,546 cases in 2025
Dengue fever is the health risk Phuket actually has, and the one visitors most often ask about after the beach flags. The series is the Department of Disease Control's weekly situation report for Health Region 11, published as open data with one row per district and sub-district and one row for the province; only the province row is used here, so nothing is double-counted. Cases are reports under the R506 surveillance system by epidemiological week — week 1 runs from 1 January to the first Saturday — and the monthly figures assign each week to the month that contains its Wednesday, which is why the month table carries a weeks column. In 2025 Phuket reported 1,546 cases and 1 death over 53 weeks, about 29.2 cases a week for a province of roughly 420,000 registered residents and many more actual ones.
The shape of the year follows the rain with a lag: the peak month was July 2025 with 280 cases and the quietest December 2025 with 41; 67% of the year's cases fell in May–October, the south-west monsoon months when standing water breeds the Aedes mosquito that carries the virus. The peak week was week 26 with 82 cases. The practical reading for a visitor is about behaviour, not fear: the Aedes mosquito bites by day, in and around houses and gardens rather than on the beach, so repellent at dawn and dusk, screens or air-conditioning at night and no standing water on a villa terrace do most of the work. Dengue is treated in every hospital on the island; the test is quick and the disease is dangerous mainly on a second infection, which is why residents take it more seriously than tourists do. Only 2025 is on file so far: the open-data file publishes the current year, and earlier years will be added from the archived reports as they are located; no historical figure is estimated in the meantime.
Coverage, gaps and updates
Three sources, three cadences. The sea temperature is recomputed for the last three complete months on the 1st and the 8th of every month by the same routine that refreshes the land climate file, so a revised reanalysis month replaces the earlier value; older months are left exactly as committed. PM2.5 is collected on the 5th of every month for the previous month from the Air4Thai hourly service and appended, never revised. The dengue file is re-read on the same day and the current year replaced in full, because the DDC report adds late notifications to earlier weeks. Every figure carries its month or week; where a source has no value the cell is empty, and no month is interpolated.
The three series are free to reuse under CC BY 4.0 with attribution to phukettravels.com and the named sources; the CSV below carries every month with sea temperature (mean, lowest day, warmest day), PM2.5 (monthly mean, days above 37.5 and 15 µg/m³) and dengue cases and deaths. Source: Open-Meteo Marine API, daily sea-surface temperature at 7.99°N 98.28°E, 2022-12–2026-08. Source: Air4Thai, Pollution Control Department — station Municipal Health Center, Talat Yai, Mueang Phuket, hourly PM2.5. Source: Department of Disease Control, Ministry of Public Health — dengue situation report, Health Region 11, Phuket province row. Retrieved 2026-09-05. The land climate normals — rain, sunshine, temperature and rough-sea days — are on the best-time page, and every external source with its URL and licence is on the sources page.
Frequently asked questions
When is the sea warmest in Phuket?
May, with a normal of 31.0 °C and daily maxima up to 32.3 °C — the end of the dry season before the south-west monsoon mixes the water. The single warmest month on record is May 2024 (31.8 °C).
Is the sea cold in Phuket during the monsoon?
No. The coolest normal is 28.8 °C in January, and the lowest single month on record 28.6 °C (January 2023). What changes in the monsoon is the swell and the red flags, not the temperature.
Does Phuket have a PM2.5 haze season?
The PCD monitor in Phuket Town recorded a monthly mean of 11.3 µg/m³ in August 2026 with 0 days above Thailand's 37.5 µg/m³ standard. Phuket is far from the northern burning season; the months to watch are February–April, and the series on this page grows by one month every refresh so those months will be reported as measured, not assumed.
How many dengue cases does Phuket have (2025)?
1,546 reported cases and 1 death in 2025 over 53 epidemiological weeks (Department of Disease Control, Health Region 11 report), peaking in July 2025 with 280 cases; 67% of the year's cases fell in May–October. The Aedes mosquito bites by day; repellent and no standing water are the practical defence.
Open data
Download sea temperature, PM2.5 and dengue by month as CSV · Full dataset, JSON
CC BY 4.0 — free to use with attribution to phukettravels.com, Open-Meteo Marine API, Air4Thai, Pollution Control Department and the Department of Disease Control, Ministry of Public Health. All sources · Statistics · Fuel, wages and electricity · Monsoon season guide