BANGKOK, THAILAND – From August 18 to 20, rain in the north and upper northeast will increase sharply. The Thai weather service warns of heavy to very heavy rain, flash floods, runoff from forests, and overflowing rivers.
The monsoon trough will shift southward, hitting the north and upper northeast hardest. Local downpours could trigger dangerous flooding in low-lying areas and near waterways.
Monsoon trough brings the rain front
A monsoon trough currently sits over the upper north, northern Laos, and northern Vietnam. At the same time, a strong southwest monsoon covers the Andaman Sea, Thailand, and the Gulf of Thailand.
This pattern holds from August 18 to 20. The trough then moves over the north and upper northeast, strengthening rainfall there.
North: thunderstorms all week
The weather service expects thunderstorms across most of the north for the entire seven-day forecast. Local heavy rain falls throughout, with very heavy rain in some spots from August 18 to 20.
Overnight lows range from 23 to 27 degrees Celsius, highs from 30 to 35 degrees. Southwest winds blow at 10 to 20 kilometres per hour.
Upper northeast: heavy to very heavy rain
From August 14 to 17, thunderstorms and local heavy rain hit large parts of the northeast. From August 18 to 20, thunderstorms cover most of the region, with heavy to very heavy rain in some areas.
Temperatures sit at 23 to 27 degrees at night and 31 to 35 degrees during the day. Southwest winds reach 10 to 20 kilometres per hour.
Central region and Bangkok: rain increasing too
In the central region, thunderstorms bring rain to large areas from August 14 to 17. From August 18 to 20, thunderstorms are possible in most of the region, with local heavy rain. Southwest winds blow at 10 to 25 km/h, with overnight lows of 23 to 28 degrees and daytime highs of 30 to 36 degrees.
For Bangkok and surrounding areas, the weather service reports thunderstorms across large areas and local heavy rain at first. From August 18, thunderstorms are expected in 60 to 70 per cent of the area, with local heavy rain. Temperatures range from 25 to 28 degrees at night and 32 to 35 degrees during the day.
East: heavy rain and higher waves
Thunderstorms and local heavy rain are expected across most of the eastern region throughout the period. Southwest winds blow at 20 to 35 km/h from August 14 to 18, then 20 to 40 km/h from August 19 to 20.
Waves reach about two metres from August 14 to 18, higher than two metres during thunderstorms. From August 19 to 20, waves hit two to three metres, exceeding three metres during storms. Temperatures range from 23 to 28 degrees at night and 30 to 35 degrees during the day.
Gulf of Thailand: storms and rough seas
On the east coast of the Gulf of Thailand, thunderstorms cover large areas from August 14 to 18. From August 19 to 20, thunderstorms hit 30 to 40 per cent of the area. Winds reach 15 to 35 km/h, later 20 to 35 km/h.
Waves near the coast are about one metre, reaching one to two metres further out. During thunderstorms, they can exceed two metres. Temperatures range from 23 to 27 degrees at night and 32 to 36 degrees during the day.
Andaman Sea: rough conditions persist
On the west coast along the Andaman Sea, thunderstorms cover 60 to 70 per cent of the area from August 14 to 18, with local heavy rain. From August 19 to 20, thunderstorms affect 40 to 60 per cent of the area. From Phang Nga northward, winds blow at 20 to 40 km/h from August 14 to 16 and again from August 19 to 20.
Waves reach two to three metres there, more than three metres during thunderstorms. Further south from Phuket on the Andaman Sea coast, waves stay mostly at one to two metres, rising above two metres during storms. From August 17 to 18, north of Phang Nga, waves are expected at around two metres, exceeding two metres during thunderstorms.
Small boats ordered to stay ashore
The weather service urges mariners to navigate carefully and avoid thunderstorm areas throughout the period. Small boats on the upper Andaman Sea should not leave port from August 14 to 16 and from August 19 to 20.
Small boats in the upper Gulf of Thailand face a sailing ban from August 19 to 20. The warning for heavy rain and accumulated rainfall in the north and upper northeast also applies from August 18 to 20. In the north and upper northeast, rain can be very heavy in some places during this period.
said the Thai Meteorological Department.