Monsoon brings heavy rain and rough seas across Thailand
The East has the widest thunderstorm coverage at 60%, while Bangkok faces a 30% chance and upper Andaman waves may top 3 metres
The Thai Meteorological Department (TMD) warned on Tuesday (August 25, 2026) that isolated heavy rain would continue in the North, upper Northeast and western Central region over the next 24 hours.
The East is forecast to have the widest thunderstorm coverage, at 60% of the region, while Bangkok and surrounding provinces will experience thunderstorms mainly between the afternoon and evening.
A rather strong south-westerly monsoon is covering the Andaman Sea, Thailand and the Gulf of Thailand. A monsoon trough also extends across upper Myanmar and upper Laos into Tropical Storm Narra over the Gulf of Tonkin.
Residents in areas affected by heavy and accumulated rainfall were advised to remain alert to possible hazards.
Rough seas and warning for small boats
Waves in the upper Andaman Sea are forecast to reach 2-3 metres and exceed 3 metres during thunderstorms.
The upper Gulf of Thailand will have waves of about 2 metres, rising above 2 metres in stormy areas.
Mariners in the Andaman Sea and the Gulf of Thailand should proceed with caution and avoid sailing through thunderstorms. Small boats in the upper Andaman Sea were advised to remain ashore.
Forecast by region
The following forecast covers the period from 6am on Tuesday to 6am on Wednesday (August 26, 2026).
Bangkok and surrounding provinces
- Thunderstorms are forecast across 30% of the area, mainly between the afternoon and evening.
- Minimum temperature: 26-28C
- Maximum temperature: 33-35C
- South-westerly winds: 10-25 km/h
North
- Thunderstorms are expected across 40% of the region, with isolated heavy rain in Mae Hong Son, Chiang Rai, Phayao, Nan and Tak.
- Minimum temperature: 23-27C
- Maximum temperature: 32-34C
- South-westerly winds: 10-20 km/h
Northeast
- Thunderstorms are forecast across 30% of the region, with isolated heavy rain in Bueng Kan, Sakon Nakhon and Nakhon Phanom.
- Minimum temperature: 24-26C
- Maximum temperature: 29-34C
- South-westerly winds: 10-25 km/h
Central region
- Thunderstorms are expected across 30% of the region, with isolated heavy rain in Kanchanaburi.
- Minimum temperature: 23-26C
- Maximum temperature: 33-35C
- South-westerly winds: 10-25 km/h
East
- Thunderstorms are forecast across 60% of the region, mainly in Chanthaburi, Trat, Nakhon Nayok and Prachin Buri.
- Minimum temperature: 23-28C
- Maximum temperature: 31-34C
- South-westerly winds: 20-35 km/h
- Waves: about 2 metres, rising above 2 metres during thunderstorms
South, east coast
- Thunderstorms are expected across 30% of the region, mainly in Surat Thani, Nakhon Si Thammarat, Songkhla, Yala and Narathiwat.
- Minimum temperature: 23-26C
- Maximum temperature: 32-36C
- From Surat Thani northwards: south-westerly winds of 20-35 km/h, with waves of 1-2 metres, about 2 metres offshore and above 2 metres during thunderstorms
- From Nakhon Si Thammarat southwards: south-westerly winds of 15-35 km/h, with waves of about 1 metre, rising to 1-2 metres offshore and above 2 metres during thunderstorms
South, west coast
- Thunderstorms are forecast across 40% of the region, mainly in Ranong, Phang Nga, Phuket and Krabi.
- Minimum temperature: 23-27C
- Maximum temperature: 30-33C
- From Phang Nga northwards: south-westerly winds of 20-40 km/h, with waves of 2-3 metres and above 3 metres during thunderstorms
From Phuket southwards: south-westerly winds of 15-35 km/h, with waves of 1-2 metres and above 2 metres during thunderstorms
