Thailand braces for monsoon rain, flash floods and high waves
Heavy to very heavy rain is forecast in several regions, with flood risks in low-lying areas and small boats advised to stay ashore.
- A strong southwest monsoon is causing heavy to very heavy rain across most of Thailand, including the North, Central, East, South, and Bangkok regions.
- Authorities are warning the public about the risk of flash floods and run-off, particularly in low-lying areas and on foothills near waterways.
- High waves are expected in the Andaman Sea and Gulf of Thailand, reaching 2-3 meters and even higher during thundershowers, prompting warnings for mariners and small boats.
The Thai Meteorological Department forecast heavy rain in parts of upper Thailand over the next 24 hours, covering the North, Northeast, Central region, Bangkok and surrounding provinces, on Tuesday (May 19, 2026).
Heavy to very heavy rain is also expected in parts of the South’s west coast and the East, as the rather strong southwest monsoon covers the upper Andaman Sea and Thailand, while a low-pressure cell lies over upper Vietnam.
People are advised to beware of heavy to very heavy rain and accumulated rainfall, which may trigger flash floods and run-off, especially on foothills near waterways and in low-lying areas.
They are also advised to take care of their health during changing weather conditions.
Waves in the upper Andaman Sea are expected to be rather strong, reaching 2-3 metres and rising above 3 metres in thundershower areas.
In the lower Andaman Sea and the upper Gulf of Thailand, waves are expected to be about 2 metres high and above 2 metres in thundershower areas.
Mariners in these areas should proceed with caution and avoid sailing in thundershowers, while small boats in the upper Andaman Sea should stay ashore.
Weather forecast for Thailand from 6am on Tuesday (May 19) to 6am on Wednesday (May 20)
North
- Thunderstorms are forecast in 60% of the area, with isolated heavy rain.
- Heavy rain is expected in Chiang Mai, Tak, Sukhothai, Uttaradit, Kamphaeng Phet, Phichit, Phitsanulok and Phetchabun.
- Minimum temperature: 24-26 degrees Celsius
- Maximum temperature: 35-38 degrees Celsius
- Southwesterly winds: 10-20km/h
Northeast
- Thunderstorms are forecast in 60% of the area, with isolated heavy rain.
- Heavy rain is expected in Loei, Nong Bua Lam Phu, Udon Thani, Nong Khai, Bueng Kan, Sakon Nakhon, Nakhon Phanom, Khon Kaen, Kalasin, Chaiyaphum and Nakhon Ratchasima.
- Minimum temperature: 23-25 degrees Celsius
- Maximum temperature: 32-36 degrees Celsius
- Southwesterly winds: 10-20km/h
Central region
- Thunderstorms are forecast in 60% of the area, with isolated heavy rain.
- Heavy rain is expected 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: 25-27 degrees Celsius
- Maximum temperature: 35-36 degrees Celsius
- Southwesterly winds: 10-20km/h
East
- Thunderstorms are forecast in 60% of the area, with isolated heavy to very heavy rain.
- Heavy to very heavy rain is expected in Nakhon Nayok, Prachin Buri, Chachoengsao, Chon Buri, Rayong, Chanthaburi and Trat.
- Minimum temperature: 25-27 degrees Celsius
- Maximum temperature: 32-36 degrees Celsius
- Southwesterly winds: 20-35km/h
- Waves will be about 2 metres high, rising above 2 metres in thundershower areas.
South, east coast
- Thunderstorms are forecast in 60% of the area, with isolated heavy rain.
- Heavy rain is expected in Phetchaburi, Prachuap Khiri Khan, Chumphon, Surat Thani, Nakhon Si Thammarat, Phatthalung and Songkhla.
- Minimum temperature: 24-27 degrees Celsius
- Maximum temperature: 33-35 degrees Celsius
- From Surat Thani northwards: southwesterly winds of 20-35km/h. Waves will be about 2 metres high, rising above 2 metres offshore and in thunderstorm areas.
- From Nakhon Si Thammarat southwards: southwesterly winds of 15-35km/h. Waves will be 1-2 metres high, about 2 metres offshore and above 2 metres in thundershower areas.
South, west coast
- Thunderstorms are forecast in 70% of the area, with heavy rain in many places and very heavy rain in some areas.
- Heavy to very heavy rain is expected in Ranong, Phang Nga, Phuket, Krabi, Trang and Satun.
- Minimum temperature: 23-25 degrees Celsius
- Maximum temperature: 30-34 degrees Celsius
- From Phuket northwards: southwesterly winds of 20-40km/h. Waves will be 2-3 metres high, rising above 3 metres in thundershower areas.
- From Krabi southwards: southwesterly winds of 20-35km/h. Waves will be about 2 metres high, rising above 2 metres in thundershower areas.
Bangkok and the surrounding provinces
- Thunderstorms are forecast in 60% of the area, with isolated heavy rain.
- Minimum temperature: 26-28 degrees Celsius
- Maximum temperature: 35-36 degrees Celsius
- Southwesterly winds: 10-20km/h
