Thailand Rainy Season by Month and Region: Andaman, Gulf, North and Bangkok

When is the rainy season in Thailand?

There are two monsoons, so there are two rainy seasons, and they hit different coasts at different times. The southwest monsoon brings rain to the Andaman side (Phuket, Krabi, Koh Lanta), the north and Bangkok from about May to October. Then the wind flips, and from October the north-east monsoon pushes rain across the Gulf of Thailand onto Koh Samui and Koh Phangan, where it peaks in November.

So the honest answer to "when is it rainy in Thailand" is "where?". Here are five places, twelve months, rain in mm:

Read it by row. Phuket is dark from May to October and clear from January to March. Koh Samui is clear in the middle of the year, when Phuket is wettest, and its worst month is November. Bangkok and Chiang Mai peak between August and October. A rainy day here is a day with at least four millimetres of rain, which matches what rain gauges count, so drizzle is not included; the method is on our methodology page.

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What does the Andaman monsoon look like?

On the Andaman coast it is a clear six-month season. Phuket gets 369 mm in May and stays between 295 and 434 mm a month until October, with rain on 13 to 19 days of each month. Krabi is similar, from 257 to 356 mm. The sea is rough, some boats stop, and a number of beach places close. November (212 mm in Phuket) is a shoulder month, and December (80 mm) is the first reasonably settled one. January to March is the clean window, with 23 mm in Phuket in February. For the detail, see Phuket in November and Krabi by month.

What is the Gulf trap in October to December?

This is the one nomads get wrong. Koh Samui and Koh Phangan are among the drier places in Thailand from May to September (75 to 136 mm on Samui), which is exactly when Phuket is wettest. So people reason that the Gulf is the "wet season escape". Then they keep that logic into the winter and arrive in November, when Koh Samui gets 457 mm, more than any of our five places in any month, with rain on 18 days. December is still 318 mm.

The swap is almost exact: when Phuket dries out in December, Samui is still wet, and it does not become comfortable until February (79 mm) and March (47 mm). If you want a Thai beach in November or December, the Andaman side dries first. The Koh Samui and Koh Phangan guide has the island-level detail, and Thailand in December compares the three coasts for that month.

And the north and Bangkok?

They follow the southwest monsoon but peak later. Chiang Mai gets 220 mm in May, then rain on 22 to 24 days of the month in July and August, the highest count of any place here. It is dry from November (61 mm), with 16 mm in December and 6 mm in February. Bangkok's peak is 315 mm in both September and October, with rain on 20 days in September, and by December it is down to 9 mm. Hua Hin, on the upper Gulf, sits between the two patterns: lighter rain in the middle of the year, then 276 mm in October.

The dry months in the north are not clean-air months. From about February to April, burning in the region fills the valley with smoke, and the air is often the worst of the year even though Chiang Mai is dry (12 mm in March). See the Chiang Mai burning season guide and Chiang Mai weather by month first. For many people the rainy months, with fresh air, are the better months to be there.

Where should you be in Thailand each month?

• January and February: Phuket, Krabi and Bangkok are dry. Koh Samui is still catching up from the end of the Gulf rain (152 mm in January).
• March and April: hot everywhere. Samui and Hua Hin are the driest of our five in March. Chiang Mai has smoke.
• May to September: the Gulf coast (Samui, Phangan, Hua Hin) for the driest sea. Avoid Phuket and Krabi if you want beach days.
• October: wet nearly everywhere. Chiang Mai (161 mm) is the lightest of the five.
• November: Chiang Mai and Bangkok, which are dry or nearly. Not Samui.
• December: Bangkok, Chiang Mai, Hua Hin and Phuket. Samui is still wet.

How bad is a rainy day for work?

Less bad than the word suggests. In most places the rain comes in the afternoon or evening in short, heavy bursts, not all day. The real costs are where the rain is steadier: rough seas and lost days on the Andaman side, the heaviest Bangkok rain in September and October, and power or internet cuts in a storm. Pick accommodation with a work area you like, a power backup and a second connection, and the green season is cheap and quiet. Compare the cities month by month in Bangkok weather by month, and the best overall month for each coast in the three coasts guide.