Weather in Thailand in May

May climate overview

Daytime highs across Thailand in May run from 29.1°C (Phuket) to 33.3°C (Bangkok). In Bangkok about 100% of May days reach 25°C. Nights average 25.9°C; the coldest 10% of nights in Phuket fall to 25°C or below.

Rainfall in May

Expect around 22 rainy days (1 mm or more) in May, with Chiang Mai the driest (14 days) and Khao Lak the wettest (27 days). The wettest May at Bangkok between 1991 and 2020 was 2017 with 334 mm; the driest was 1992 with 49 mm.

Sea temperature

The sea averages 30.3°C around Thailand in May - warmest at Bangkok (30.6°C). That is comfortable for swimming.

Sunshine and daylight

Around 2.5 hours of sunshine a day on average, out of 12.6 hours of daylight (sunshine estimated from cloud cover).

May against the rest of the year in Thailand

May is the 3rd warmest month of the twelve in Thailand. It is 1.3°C cooler than April and 0.8°C cooler in June. The hottest month here is April (32°C) and the coolest December (29°C).

Which part of Thailand in May?

• Most sunshine: Chiang Mai, 4.0 h a day.
• Driest: Chiang Mai, about 14 rainy days.
• Warmest sea: Bangkok, 31°C.
• Hottest: Bangkok, 33°C by day - intense for sightseeing.
• Coolest (better for walking and cities): Phuket, 29°C.

What to pack for Thailand in May

Based on the averages: light, loose clothing and serious sun protection - midday highs sit around 31°C; a rain jacket - roughly 22 wet days; swimwear - the sea is 30°C.

Similar weather elsewhere in May

Within 1.5°C of Thailand's May daytime average: Puerto Vallarta (32°C, sea 26°C), Guanacaste (31°C, sea 29°C), Hanoi (31°C), Hurghada (31°C, sea 25°C), Las Vegas (30°C). See the full ranking for May.

Chiang Mai for fewer rainy days, Bangkok for heat

Chiang Mai is the strongest choice if avoiding rain matters more than being beside the sea. Its 14 rainy days compare with 20 in Bangkok, although both reach 33°C by day, so fewer wet days do not mean cooler afternoons. Plan more demanding outdoor time away from midday and leave room for breaks from the heat. Chiang Mai also offers slightly cooler nights at 24°C, against Bangkok's 26°C. Bangkok suits travellers comfortable with hot days and warm evenings, rather than anyone seeking relief from the heat. For either destination, pack light clothing and rain protection instead of relying on a dry forecast throughout your stay.

Koh Samui has the coastal edge, but expect rain

Koh Samui has the fewest rainy days among the coastal destinations listed, with 22 compared with Phuket's 25 and 27 in both Krabi and Khao Lak. That makes it the better fit for a coast-focused trip if reducing rain exposure is your priority, not a promise of dry beach weather. Daytime temperatures are similar: Koh Samui, Krabi and Khao Lak average 30°C, while Phuket is slightly cooler at 29°C. All have a 30°C sea, so cold water is not the main concern. Choose a coastal stay with flexible plans, and let local conditions guide swimming rather than assuming warm water means suitable conditions.

Build your days around heat and changeable weather

The practical catch in May is that warmth does not come with dependable sunshine. Thailand averages 2.5 hours of sunshine and 22 rainy days, so leave space to change outdoor plans rather than filling every day with weather-dependent activities. A rainy-day figure does not tell you how long rain lasts or when it falls; do not count on a fixed daily window of dry weather. Lightweight clothing, something to keep belongings dry and footwear you can manage in wet conditions are sensible choices. With average nights of 26°C, evenings offer limited cooling, so choose accommodation where you can comfortably rest from the heat.