Heavy rain warning spans Thailand as flash flood and runoff risks rise
People in affected areas have been urged to beware of accumulated rain, flash floods and runoff, while mariners are warned of rough seas.
- Thailand's Meteorological Department has issued a heavy to very heavy rain warning across the country, lasting until Thursday, May 21.
- The intense rainfall creates a significant risk of flash floods and runoff, particularly on foothill slopes and in low-lying areas.
- Affected regions include the North, upper Northeast, Central, East, and the South’s west coast.
- The warning also includes strong winds and high waves (2-3 meters or more) in the Andaman Sea, prompting a caution for mariners and an advisory for small boats to remain ashore.
The Thai Meteorological Department has issued an announcement warning of heavy to very heavy rain across Thailand and strong winds and waves in the Andaman Sea, with impacts continuing until Thursday (May 21, 2026).
Upper Thailand is expected to see heavy rain in some places in the North, the upper Northeast and the Central region, with heavy to very heavy rain in some areas on the South’s west coast and in the East.
People in these areas are asked to beware of danger from heavy to very heavy and accumulated rain, which may cause flash floods and runoff, especially on foothill slopes near waterways and in low-lying areas.
This is because the southwest monsoon blowing across the Andaman Sea, Thailand, and the Gulf of Thailand is rather strong.
The public should also take care of their health during changing weather conditions.
Wind and waves in the Andaman Sea and the Gulf of Thailand are also rather strong.
In the upper Andaman Sea from Phuket province northwards, waves are 2–3 metres high, rising to more than 3 metres in thunderstorm areas.
In the lower Andaman Sea from Krabi province southwards, and in the upper Gulf of Thailand, waves are about 2 metres high, rising to more than 2 metres in thunderstorm areas.
Mariners in these areas are urged to navigate with caution and avoid sailing in thunderstorm areas, while small boats in the upper Andaman Sea should remain ashore.
In addition, from Tuesday (May 19) to Thursday (May 21), rainfall in Thailand will increase, with heavy to very heavy rain in some places, mostly on the country’s western side, covering areas of the North, the upper Northeast, the Central region, the East and the South’s west coast.
This is due to the rather strong southwest monsoon blowing across the Andaman Sea, Thailand and the Gulf of Thailand, together with a low-pressure area lying over the coast of upper Vietnam.
The public is therefore asked to follow announcements from the Thai Meteorological Department.
Information is available via the department’s website, or by calling 0-2399-4012-13 and 1182, 24 hours a day.
Issued on Monday (May 18) at 5pm.
