TMD warns strong monsoon to bring heavy rain across Thailand’s regions

The Thai Meteorological Department (TMD) on Wednesday (May 20, 2026) forecast continued rain across Thailand over the next 24 hours, with heavy to very heavy rain in some areas of the South’s west coast, the Northeast and the East.

Isolated heavy rain was also forecast for the North and the Central region, including Bangkok and surrounding provinces.

The conditions were caused by a rather strong southwesterly monsoon covering the upper Andaman Sea and Thailand, together with a low-pressure cell over upper Vietnam.

People were advised to beware of heavy to very heavy rain and accumulated rainfall, which could trigger flash floods and run-off, especially in foothill areas near waterways and low-lying areas, and to take care of their health during changing weather conditions.

Waves in the upper Andaman Sea were forecast to be rather strong, reaching 2-3 metres and rising above 3 metres in thundershowers.

In the lower Andaman Sea and the upper Gulf of Thailand, waves were expected to be about 2 metres high and above 2 metres in thundershowers.

Mariners in these areas were advised to proceed with caution and avoid sailing in thundershowers, while small boats in the upper Andaman Sea should remain ashore.

Forecast for Thailand from 6am on Wednesday (May 20, 2026) to 6am on Thursday (May 21, 2026)

North

• Thunderstorms are forecast across 60% of the area, with isolated heavy rain in Nan, Tak, Sukhothai, Uttaradit, Kamphaeng Phet, Phichit, Phitsanulok and Phetchabun.
• Minimum temperature: 24-26 degrees Celsius
• Maximum temperature: 33-38 degrees Celsius
• Southwesterly winds: 10-20 km/h

Northeast

• Thunderstorms are forecast across 70% of the area, with isolated heavy to very heavy rain in Loei, Nong Khai, Bueng Kan, Nong Bua Lamphu, Udon Thani, Sakon Nakhon, Nakhon Phanom, Chaiyaphum, Khon Kaen, Kalasin, Maha Sarakham, Mukdahan, Roi Et, Yasothon, Amnat Charoen, Nakhon Ratchasima, Si Sa Ket and Ubon Ratchathani.
• Minimum temperature: 23-25 degrees Celsius
• Maximum temperature: 30-34 degrees Celsius
• Southwesterly winds: 10-20 km/h

Central region

• Thunderstorms are forecast across 60% of the area, with isolated heavy rain in Nakhon Sawan, Uthai Thani, Chai Nat, Lop Buri, Saraburi, Sing Buri, Ang Thong, Phra Nakhon Si Ayutthaya, Suphan Buri, Nakhon Pathom, Kanchanaburi and Ratchaburi.
• Minimum temperature: 24-26 degrees Celsius
• Maximum temperature: 31-35 degrees Celsius
• Southwesterly winds: 10-20 km/h

East

• Thunderstorms are forecast across 60% of the area, with isolated heavy to very heavy rain in Nakhon Nayok, Prachin Buri, Chachoengsao, Chonburi, Rayong, Chanthaburi and Trat.
• Minimum temperature: 25-28 degrees Celsius
• Maximum temperature: 31-34 degrees Celsius
• Southwesterly winds: 20-35 km/h
• Waves are forecast to be about 2 metres high, and above 2 metres in thundershowers.

South, east coast

• Thunderstorms are forecast across 60% of the area, with isolated heavy rain in Chumphon, Surat Thani, Nakhon Si Thammarat, Phatthalung and Songkhla.
• Minimum temperature: 23-26 degrees Celsius
• Maximum temperature: 30-35 degrees Celsius
• From Surat Thani northwards: southwesterly winds at 20-35 km/h. Waves are forecast to be about 2 metres high, and above 2 metres offshore and in thundershowers.
• From Nakhon Si Thammarat southwards: southwesterly winds at 15-35 km/h. Waves are forecast to be 1-2 metres high, about 2 metres offshore, and above 2 metres in thundershowers.

South, west coast

• Thunderstorms are forecast across 70% of the area, with heavy rain in many areas and very heavy rain in some places in Ranong, Phang Nga, Phuket, Krabi, Trang and Satun.
• Minimum temperature: 23-25 degrees Celsius
• Maximum temperature: 26-33 degrees Celsius
• From Phuket northwards: southwesterly winds at 20-40 km/h. Waves are forecast to be 2-3 metres high, and above 3 metres in thundershowers.
• From Krabi southwards: southwesterly winds at 20-35 km/h. Waves are forecast to be about 2 metres high, and above 2 metres in thundershowers.

Bangkok and the surrounding provinces

• Thunderstorms are forecast across 60% of the area, with isolated heavy rain.
• Minimum temperature: 26-28 degrees Celsius
• Maximum temperature: 33-36 degrees Celsius
• Southwesterly winds: 10-20 km/h