Monsoon brings heavy rain and rough seas to Thailand
TMD says Narra will not enter Thailand, but heavy rain and waves above three metres are forecast under a rather strong southwest monsoon.
Heavy rain is forecast in parts of northern, northeastern and southern Thailand over the next 24 hours, while waves in the upper Andaman Sea could exceed three metres during thunderstorms, the Thai Meteorological Department (TMD) said.
The department issued its regional forecast at 5pm on Tuesday (August 25, 2026), covering the period from 6pm on Tuesday to 6pm on Wednesday.
Small boats in the upper Andaman Sea were advised to remain ashore. Other vessels in the Andaman Sea and the Gulf of Thailand should proceed with caution and avoid areas affected by thunderstorms.
Heavy rain risk in three regions
Thailand will experience isolated thunderstorms, with heavy rain possible in parts of the North, upper Northeast and west coast of the South.
Residents in those areas were advised to be alert to hazards caused by heavy and accumulated rainfall.
The conditions are being driven by a rather strong southwest monsoon prevailing over the Andaman Sea, Thailand and the Gulf of Thailand.
A weak monsoon trough also extends across upper Myanmar and upper Laos towards Tropical Storm Narra over the Gulf of Tonkin.
Upper Andaman waves may exceed three metres
Waves in the upper Andaman Sea are forecast to reach 2-3 metres and exceed three metres in thunderstorms.
The upper Gulf of Thailand will have waves of about two metres, rising above two metres in stormy areas.
Marine conditions will also be rough off eastern Thailand and both coasts of the South, with wave heights varying according to location.
Narra forecast to reach southern China
Tropical Storm Narra is forecast to make landfall in southern Guangxi, China, between August 25 and 26.
The TMD said the storm was not expected to move into Thailand.
People planning to travel to the affected part of China were advised to check weather conditions before departure.
Regional forecast
North: Thunderstorms are forecast over 40% of the region, with isolated heavy rain in Mae Hong Son, Chiang Rai, Phayao, Nan and Tak. Temperatures will range from 23-27°C to 32-34°C, with southwesterly winds of 10-20 kilometres per hour.
Northeast: Thunderstorms are expected over 30% of the region, with isolated heavy rain in Bueng Kan, Sakon Nakhon, Nakhon Phanom and Mukdahan. Temperatures will range from 24-26°C to 29-34°C, with southwesterly winds of 10-25km/h.
Central region: Thunderstorms are forecast over 30% of the area, mainly in Nakhon Sawan, Uthai Thani, Kanchanaburi and Ratchaburi. Temperatures will range from 23-26°C to 33-35°C, with southwesterly winds of 10-25km/h.
Bangkok and surrounding provinces: Thunderstorms are expected over 30% of the area, mostly between the afternoon and evening. Temperatures will range from 26-28°C to 33-35°C, with southwesterly winds of 10-25km/h.
East: Thunderstorms are forecast over 60% of the region, mainly in Nakhon Nayok, Prachin Buri, Chanthaburi and Trat. Temperatures will range from 24-28°C to 31-34°C, with southwesterly winds of 20-35km/h. Waves will be about two metres and exceed two metres in thunderstorms.
South, east coast: Thunderstorms are expected over 30% of the region, mainly in Surat Thani, Nakhon Si Thammarat, Songkhla, Yala and Narathiwat. Temperatures will range from 23-26°C to 32-36°C.
From Surat Thani northwards, southwesterly winds will reach 20-35km/h. Waves will be 1-2 metres, around two metres offshore and above two metres in thunderstorms.
From Nakhon Si Thammarat southwards, southwesterly winds will reach 15-35km/h. Waves will be about one metre, rising to 1-2 metres offshore and above two metres in thunderstorms.
South, west coast: Thunderstorms are forecast over 60% of the region, with isolated heavy rain in Phuket, Krabi, Trang and Satun. Temperatures will range from 23-26°C to 30-33°C.
From Phang Nga northwards, southwesterly winds will reach 20-40km/h. Waves will be 2-3 metres and exceed three metres in thunderstorms.
From Phuket southwards, southwesterly winds will reach 15-35km/h. Waves will be 1-2 metres and exceed two metres in thunderstorms.
