Best time to visit Phuket — data, not opinions

Why medians and not 'average weather'

Most 'best time to visit Phuket' pages repeat a chart copied from a chart copied from a tourist-board leaflet. The numbers on this page are computed from a reanalysis dataset — a weather model constrained by satellite and station observations — for one grid point on Phuket's west coast, month by month, from January 2015 to the latest complete month. For each calendar month we take the median of the yearly values: the middle value, not the mean, so one freak month (a tropical storm, a failed monsoon) does not drag the whole picture.

We publish the sample size next to the numbers because it matters. Rain and temperature normals rest on eleven years; wave and rough-sea figures rest on four, because the marine model only goes back to 2022-01. Four years is enough to see the seasonal shape and not enough to trust a single day's difference between two months. Where a figure would rest on nothing, the cell says so instead of showing a plausible number.

What 'rain' means here

Three columns describe rain, and they answer three different questions. Millimetres per month is total volume: how much water fell. Rain days is how many days had any measurable rain — including a ten-minute shower at four in the afternoon, which is why even February shows several. Heavy-rain days is the number of days with a genuinely wet total, the kind that cancels a boat trip or floods the road to the beach; that is the column to watch if you are deciding between two months in the green season.

Read together, the pattern is clear. From November to March rain is light and brief. April is warm and humid with the first afternoon storms. From May the south-west monsoon settles in and the monthly totals triple; May and October are the wettest months by volume, September and October have the most heavy-rain days. November is still wet on the west coast but the sea has already calmed, and by December the totals halve again.

The sea: the number most pages leave out

Rain is inconvenient; the sea is the real seasonal difference on Phuket. From May to October the south-west monsoon pushes a swell onto the west-coast beaches — Patong, Karon, Kata, Kamala, Surin, Bang Tao, Nai Thon, Mai Khao — and lifeguards raise red flags on the rough days. The 'rough-sea days' column counts the days in a median month when the modelled maximum wave height crosses the threshold at which swimming becomes dangerous at an exposed beach. July is the peak, with 13 such days in a median month; from November to April the count is zero.

This is also why the east and south coasts matter in the green season. Chalong, Panwa, Rawai and the eastern side face Phang Nga Bay, sheltered from the monsoon swell; the water there is flat when Patong is red-flagged, though the beaches are smaller and the water less clear. If you are coming between June and September and want to swim every day, the area you choose matters more than the month.

Temperature and sunshine barely move

Phuket sits eight degrees north of the equator, and the temperature table shows it: median daily highs span only 28.7–31.7 °C across the whole year and nights stay between 24.1 and 25.9 °C. March is the hottest month, and the humidity numbers — mid-seventies in the dry season, mid-eighties in the wet — explain why April feels harder than the thermometer suggests.

Sunshine follows the rain in mirror image: March has the most (343 hours in a median month, about 11.4 a day), September the least (248 hours, still 8.3 a day). Even the dullest month of the green season has more daily sunshine than a northern European summer, which is the honest case for travelling then: cheaper rooms, empty beaches, a couple of rain bursts a day and a sea you have to be careful with.

So when should you come?

For beaches and boat trips with the least uncertainty: December to March. February is the driest, the sea is flat everywhere, and the price for that certainty is the highest hotel rates of the year and the busiest beaches. If you want the dry season without the peak, late November and March are the edges — still dry and calm, with rates already sliding.

For value: May–June and September–October, in that order of comfort. Monthly rain is high, but heavy-rain days stay in single figures until September, and the rough-sea count in May is a third of July's. Book on the east or south coast if daily swimming is the point. For long stays — a month or a season — the calculus changes again: a villa month in the green season is markedly cheaper, the rain is a daily interlude rather than a holiday-wrecker, and the island is quiet. The price side of that decision lives in the index; this page only settles the weather.

Source and method

Weather: Open-Meteo (ERA5), 2015–2026, licensed CC BY 4.0, grid point 7.89°N 98.30°E. Waves: Open-Meteo marine model, from 2022-01. Normals are medians of the monthly values for 2015–2025; the 'last twelve months' table uses the raw monthly values. Rough-sea days are days whose modelled maximum wave height exceeds the pipeline's swimming-safety threshold. Nothing is interpolated: an empty cell means no observation.