North and Northeast brace for very heavy rain and flash floods through Friday

The Thai Meteorological Department issued Warning No. 10 on Thursday, cautioning that heavy to very heavy rain would affect parts of upper Thailand through Friday (August 21).

The heaviest rainfall is expected in the North and Northeast as a monsoon trough lies across northern and upper northeastern Thailand. A relatively strong southwesterly monsoon is also prevailing over the Andaman Sea, Thailand and the Gulf of Thailand.

People in affected areas are advised to remain alert to the dangers posed by heavy and accumulated rainfall, which could trigger flash floods and rapid run-off, particularly on foothills near waterways and in low-lying areas.

Motorists should avoid routes that are repeatedly affected by flooding, especially low-lying roads where temporary waterlogging may occur.

Rough seas and small-boat warning

Waves in the upper Andaman Sea and upper Gulf of Thailand are expected to reach 2–3 metres, rising above 3 metres during thunderstorms.

In the lower Andaman Sea, waves will be about 2 metres high and may exceed 2 metres in stormy areas.

Vessels in the Andaman Sea and Gulf of Thailand should proceed with caution and avoid areas experiencing thunderstorms.

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

Seven-day weather outlook

From August 20–21, rainfall is forecast to increase across the North and Northeast, with heavy to very heavy rain expected in some areas.

The monsoon trough will shift southwards across northern and upper northeastern Thailand, while the relatively strong southwesterly monsoon continues to cover the Andaman Sea, Thailand and the Gulf.

Waves in the upper Andaman Sea will reach 2–3 metres and exceed 3 metres during thunderstorms. In the upper Gulf, waves will be about 2 metres high and rise above 2 metres in stormy areas.

From August 22–26, rainfall is expected to decrease across Thailand, although isolated heavy rain will remain possible, mainly in the North, Northeast, East and along the west coast of the South.

During this period, the monsoon trough will move northwards across Myanmar, the upper North and upper Laos before extending into a low-pressure area over northern Vietnam.

The southwesterly monsoon over the Andaman Sea, Thailand and the Gulf will weaken to moderate strength.

Waves in the upper Andaman Sea will be about 2 metres high and exceed 2 metres during thunderstorms. In the upper Gulf, waves will reach 1–2 metres and rise above 2 metres in stormy areas.