TMD warns of heavy rain, rough seas across Thailand until June 1

The Thai Meteorological Department has warned people across Thailand to brace for heavy to very heavy rain, flash floods and rough seas from May 28 to June 1, as a rather strong southwest monsoon covers the Andaman Sea, Thailand and the Gulf.

In Weather Advisory No 2 (80/2026), issued at 5pm on Wednesday, May 27, the department said a monsoon trough was lying across upper Thailand, bringing more rain and scattered heavy downpours nationwide.

Isolated very heavy rain is possible in the South, the East, the western part of the North and the western part of the Central region.

People are advised to beware of heavy rain and accumulated rainfall, which could trigger flash floods and water run-off, especially in foothill areas, near waterways and in low-lying communities.

Small boats warned to stay ashore in upper Andaman Sea

The department also warned of strong wind waves in the Andaman Sea and the upper Gulf from May 28 to June 1.

In the upper Andaman Sea, from Phuket northwards, waves are expected to reach 2-3 metres and rise above 3 metres during thundershowers.

In the lower Andaman Sea, from Krabi southwards, and in the upper Gulf, waves are forecast at around 2 metres, rising above 2 metres in thunderstorm areas.

All vessels have been advised to proceed with caution and avoid sailing through thundershowers. Small boats in the upper Andaman Sea should remain ashore during the warning period.

North to see heavy rain in some areas

For the 24-hour forecast from 6pm Wednesday to 6pm Thursday, thunderstorms are expected in 60% of the North, with heavy rain in some areas of Mae Hong Son, Chiang Mai and Tak.

Temperatures are forecast to range from 22-26°C at the lowest to 34-37°C at the highest. Southwesterly winds are expected at 10-20 kilometres per hour.

Thunderstorms forecast in Northeast and Central region

The Northeast is expected to see thunderstorms in 40% of the region, mainly in Loei, Nong Khai, Bueng Kan, Chaiyaphum, Nakhon Ratchasima, Buri Ram, Surin, Si Sa Ket and Ubon Ratchathani.

Temperatures will range from 23-26°C to 35-38°C, with southwesterly winds at 10-20km/h.

In the Central region, thunderstorms are forecast in 40% of the area, mainly in Nakhon Sawan, Uthai Thani, Suphan Buri, Phra Nakhon Si Ayutthaya, Kanchanaburi, Ratchaburi, Nakhon Pathom and Samut Songkhram.

Temperatures are expected to range from 25-26°C to 36-38°C, with southwesterly winds at 10-20km/h.

Bangkok faces thunderstorms in 30% of area

Bangkok and surrounding provinces are forecast to see thunderstorms in 30% of the area.

Temperatures are expected to range from 24-27°C to 35-38°C, with southwesterly winds at 10-20km/h.

East warned of thunderstorms and rough seas

The East is expected to see thunderstorms in 40% of the region, mainly in Nakhon Nayok, Prachin Buri, Rayong, Chanthaburi and Trat.

Temperatures will range from 24-27°C to 33-37°C. Southwesterly winds are forecast at 15-35km/h.

Waves in the eastern sea are expected to be 1-2 metres high, rising above 2 metres in thunderstorm areas.

South faces heavy rain and high waves

On the east coast of the South, thunderstorms are forecast in 40% of the region, mainly in Phetchaburi, Prachuap Khiri Khan, Chumphon, Surat Thani and Nakhon Si Thammarat.

Temperatures will range from 23-25°C to 33-36°C. Southwesterly winds are expected at 15-35km/h. Waves will be about 1 metre high, rising to 1-2 metres offshore and above 2 metres during thundershowers.

On the west coast of the South, thunderstorms are expected in 60% of the region, with heavy rain in some areas of Ranong and Phang Nga.

Temperatures will range from 24-25°C to 32-34°C.

From Phang Nga northwards, southwesterly winds are forecast at 20-35km/h, with waves around 2 metres high and above 2 metres in thunderstorm areas.

From Phuket southwards, southwesterly winds are expected at 15-35km/h, with waves of 1-2 metres and above 2 metres during thundershowers.

Next advisory due Thursday morning

The advisory took effect at 5pm on May 27. The Thai Meteorological Department said its next update would be issued at 5am on May 28.