Monsoon brings thunderstorms to northern and northeastern Thailand

The Thai Meteorological Department (TMD) warned on Thursday (August 20, 2026) that heavy to very heavy rain would affect parts of upper Thailand.

The conditions were expected to continue through Friday (August 21, 2026).

The department also identified the areas at risk.

Thursday (August 20)

Areas forecast to receive very heavy rain

• North: Mae Hong Son, Uttaradit, Sukhothai, Tak, Phitsanulok, Phichit and Phetchabun
• Northeast: Loei, Nong Khai, Nong Bua Lamphu, Udon Thani, Bueng Kan, Sakon Nakhon and Nakhon Phanom
• Central: Kanchanaburi and Ratchaburi
• East: Trat

Areas forecast to receive heavy rain

• North: Chiang Mai, Chiang Rai, Lamphun, Lampang, Phayao, Nan, Phrae and Kamphaeng Phet
• Northeast: Chaiyaphum, Khon Kaen, Kalasin, Mukdahan, Maha Sarakham, Roi Et, Yasothon, Amnat Charoen, Nakhon Ratchasima and Ubon Ratchathani
• Central: Nakhon Sawan, Uthai Thani, Chai Nat, Lop Buri, Saraburi, Nakhon Pathom, Samut Sakhon and Samut Songkhram, as well as Bangkok and surrounding provinces
• East: Nakhon Nayok, Prachin Buri, Sa Kaeo and Chanthaburi
• South: Phetchaburi, Prachuap Khiri Khan and Chumphon

Friday (August 21, 2026)

Areas forecast to receive very heavy rain

• North: Uttaradit, Phitsanulok and Tak
• Northeast: Loei, Nong Khai, Nong Bua Lamphu and Udon Thani

Areas forecast to receive heavy rain

• North: Mae Hong Son, Chiang Mai, Lamphun, Lampang, Nan, Phrae, Sukhothai, Kamphaeng Phet and Phetchabun
• Northeast: Bueng Kan, Sakon Nakhon, Nakhon Phanom and Khon Kaen
• Central: Uthai Thani, Kanchanaburi and Ratchaburi
• East: Chanthaburi and Trat

Heavy to very heavy rain is forecast in parts of Thailand, particularly in the North and Northeast, as monsoon conditions extend across the North and upper Northeast and the rather strong southwest monsoon prevails over the Andaman Sea, Thailand and the Gulf of Thailand.

The department warned that heavy and accumulated rainfall could cause flash floods and rapid run-off, especially on foothill slopes near waterways and in low-lying areas.

People should avoid routes prone to repeated flooding, particularly low-lying roads where brief inundation could occur.

Conditions in the upper Andaman Sea and upper Gulf of Thailand will be rather rough, with waves of 2–3 metres and above 3 metres in areas with thunderstorms.

Waves in the lower Andaman Sea will be about 2 metres and above 2 metres in thunderstorms.

All vessels in the Andaman Sea and Gulf of Thailand should proceed with caution and avoid thunderstorm areas.

Small boats in the upper Andaman Sea and upper Gulf should remain ashore during the period.

To ensure safety and minimise possible impacts, people were advised to plan their daily activities and journeys carefully.

They should follow announcements from the TMD through the department’s website or telephone numbers 0-2399-4012-13 and 1182, which are available around the clock.

TMD forecast for Thailand from 6pm on Thursday (August 20) to 6pm on Friday (August 21)

North

• Thunderstorms are forecast across 80% of the region, with heavy rain in many areas.
• Heavy rain is expected in Chiang Mai, Chiang Rai, Lamphun, Lampang, Phayao, Nan, Phrae and Kamphaeng Phet.
• Very heavy rain is expected in some areas of Mae Hong Son, Uttaradit, Sukhothai, Tak, Phitsanulok, Phichit and Phetchabun.
• Minimum temperature: 23–27°C.
• Maximum temperature: 27–31°C.
• Southwesterly winds: 10–20km/h.

Northeast

• Thunderstorms are forecast across 80% of the region, with heavy rain in many areas.
• Heavy rain is expected in Chaiyaphum, Khon Kaen, Kalasin, Mukdahan, Maha Sarakham, Roi Et, Yasothon, Amnat Charoen, Nakhon Ratchasima and Ubon Ratchathani.
• Very heavy rain is expected in some areas of Loei, Nong Khai, Nong Bua Lamphu, Udon Thani, Bueng Kan, Sakon Nakhon and Nakhon Phanom.
• Minimum temperature: 22–25°C.
• Maximum temperature: 26–30°C.
• Southwesterly winds: 10–20km/h.

Central

• Thunderstorms are forecast across 70% of the region, with heavy rain in some areas.
• Heavy rain is expected in Nakhon Sawan, Uthai Thani, Chai Nat, Lop Buri, Saraburi, Nakhon Pathom, Samut Sakhon and Samut Songkhram.
• Very heavy rain is expected in some areas of Kanchanaburi and Ratchaburi.
• Minimum temperature: 23–26°C.
• Maximum temperature: 29–33°C.
• Southwesterly winds: 10–25km/h.

East

• Thunderstorms are forecast across 70% of the region, with heavy rain in some areas.
• Heavy rain is expected in Nakhon Nayok, Prachin Buri, Sa Kaeo and Chanthaburi.
• Very heavy rain is expected in some areas of Trat.
• Minimum temperature: 23–28°C.
• Maximum temperature: 29–33°C.
• Southwesterly winds: 20–40km/h.
• Wave height: 2–3 metres, rising above 3 metres in areas with thunderstorms.

South (east coast)

• Thunderstorms are expected across 40% of the region, with heavy rain in parts of Phetchaburi, Prachuap Khiri Khan and Chumphon.
• Minimum temperature: 23–26°C.
• Maximum temperature: 32–36°C.
• From Surat Thani northwards, southwesterly winds will reach 20–35km/h, with waves of 1–2 metres and above 2 metres offshore and in thunderstorms.
• From Nakhon Si Thammarat southwards, southwesterly winds will reach 15–35km/h, with waves of about 1 metre, rising to 1–2 metres offshore and above 2 metres in thunderstorms.

South (west coast)

• Thunderstorms are expected across 40% of the region, mainly in Ranong and Phang Nga.
• Minimum temperature: 23–27°C.
• Maximum temperature: 28–35°C.
• From Phuket northwards, southwesterly winds will reach 20–40km/h, with waves of 2–3 metres and above 3 metres in thunderstorms.
• From Krabi southwards, southwesterly winds will reach 20–35km/h, with waves of about 2 metres and above 2 metres in thunderstorms.

Bangkok and surrounding provinces

• Thunderstorms are forecast across 70% of the area, with heavy rain in some places.
• Minimum temperature: 25–27°C.
• Maximum temperature: 32–34°C.
• Southwesterly winds: 10–25km/h.