Monsoon downpours and rough seas keep Thailand on high alert
Forecasts show continued downpours, flash-flood risks and waves above 3 metres in the upper Andaman Sea, with small boats told to stay ashore.
- Thailand is forecast to receive continuous heavy to very heavy rain, especially from May 30-31, due to a monsoon trough and a strong south-west monsoon.
- The weather system is creating rough seas, with waves in the upper Andaman Sea reaching 2-3 meters high and exceeding 3 meters in thunderstorm areas.
- Authorities have issued warnings for potential flash floods and river overflows, and have advised mariners to navigate with caution, with small boats in the upper Andaman Sea urged to stay ashore.
Thailand is forecast to see continuous rain, with heavy rain in some areas and very heavy rain in places, during May 30 and May 31, the Thai Meteorological Department (TMD) said in its advance weather outlook for the period to June 5.
The conditions are being driven by a monsoon trough lying across upper Thailand, together with a rather strong south-west monsoon prevailing over the Andaman Sea, Thailand and the Gulf of Thailand.
From June 1 to June 5, rainfall in upper Thailand is expected to decrease, though heavy rain is still forecast in some areas.
The South and the East will continue to see heavy to very heavy rain in some places, as the rather strong south-west monsoon remains over the Andaman Sea, Thailand and the Gulf of Thailand, while a low-pressure cell covers the upper Bay of Bengal and Myanmar.
Wind and waves in the upper Andaman Sea will remain rather strong throughout the period, with waves 2-3 metres high and above 3 metres in thunderstorm areas.
In the lower Andaman Sea and the upper Gulf of Thailand, waves are expected to be about 2 metres high and above 2 metres in thunderstorm areas.
Precautions
People are urged to beware of heavy rain and accumulated rainfall, which could cause flash floods, forest run-off and river overflow.
Mariners in the Andaman Sea and the Gulf of Thailand should navigate with caution and avoid sailing in thunderstorm areas throughout the period.
Small boats in the upper Andaman Sea should stay ashore from May 30 to June 5.
Regional forecast for Saturday (May 30, 2026) to Friday (June 5, 2026)
North
- May 30 to June 1: Thunderstorms are forecast in 60-70% of the area, with heavy rain in some places and very heavy rain in some areas on May 30.
- June 2 to June 5: Thunderstorms are forecast in 30-40% of the area, with heavy rain in some places, mostly in the western and upper parts of the region. South-westerly winds are expected at 10-20 km/h.
- Minimum temperature: 23-27°C.
- Maximum temperature: 31-37°C.
North-east
- May 30 to May 31: Thunderstorms are forecast in 40-60% of the area, with heavy rain in some places on Saturday (May 30, 2026).
- June 1 to June 5: Thunderstorms are forecast in 30-40% of the area. South-westerly winds are expected at 10-20 km/h.
- Minimum temperature: 23-27°C.
- Maximum temperature: 33-38°C.
Central region
- May 30 to June 1: Thunderstorms are forecast in 40-60% of the area, with heavy rain in some places and very heavy rain in some areas on May 30, mostly in the western part of the region. South-westerly winds are expected at 10-25 km/h.
- June 2 to June 5: Thunderstorms are forecast in 30-40% of the area, with heavy rain in some places, mostly in the western part of the region. South-westerly winds are expected at 10-20 km/h.
- Minimum temperature: 24-27°C.
- Maximum temperature: 32-38°C.
East
- Thunderstorms are forecast in 40-70% of the area, with heavy to very heavy rain in some places. South-westerly winds are expected at 20-35 km/h.
- Waves will be about 2 metres high and above 2 metres in thunderstorm areas.
- Minimum temperature: 25-29°C.
- Maximum temperature: 31-37°C.
South, east coast
- Thunderstorms are forecast in 60-70% of the area, with heavy rain in some places.
- South-westerly winds are expected at 15-35 km/h.
- Waves will be about 1 metre high, 1-2 metres offshore and above 2 metres in thunderstorm areas.
- Minimum temperature: 23-27°C.
- Maximum temperature: 32-37°C.
South, west coast
- Thunderstorms are forecast in 70-80% of the area, with heavy to very heavy rain in some places.
- Minimum temperature: 23-26°C.
- Maximum temperature: 30-36°C.
- From Phuket northwards: South-westerly winds are expected at 20-40 km/h. Waves will be 2-3 metres high and above 3 metres in thunderstorm areas.
- From Krabi southwards: South-westerly winds are expected at 20-35 km/h. Waves will be about 2 metres high and above 2 metres in thunderstorm areas.
Bangkok and the surrounding provinces
- Thunderstorms are forecast in 40-60% of the area, with heavy rain in some places from May 30 to May 31.
- South-westerly winds are expected at 10-25 km/h.
- Minimum temperature: 25-28°C.
- Maximum temperature: 33-37°C.
