Monsoon surge to bring heavier rain and rough seas to Thailand

The Thai Meteorological Department (TMD) has forecast more rain across Thailand over the next 24 hours, with heavy rain in some areas and very heavy rain in parts of the East and the southern west coast, on Monday (June 29, 2026).

The southwest monsoon over the Andaman Sea, Thailand and the Gulf of Thailand has strengthened, while the monsoon trough has moved down across Myanmar, upper northern Thailand and upper Laos into a low-pressure area over upper Vietnam.

People were advised to beware of thunderstorms, heavy to very heavy rain and accumulated rainfall, which could cause flash floods and forest run-off, especially in foothill areas near waterways and in low-lying areas.

Wind waves over the upper Andaman Sea are fairly strong, with waves 2-3 metres high and more than 3 metres in thunderstorms.

Waves in the lower Andaman Sea and the upper Gulf of Thailand are about 2 metres high, rising above 2 metres in thunderstorms.

Mariners in the Andaman Sea and the Gulf of Thailand were urged to proceed with caution and avoid sailing in areas with thunderstorms.

Small boats in the upper Andaman Sea should remain ashore until Friday (July 3).

Weather forecast for Thailand from 7am on Monday (June 29), to 7am on Tuesday (June 30)

North

• Thunderstorms are forecast in 40% of the area, with heavy rain in some places.
• Affected provinces: Tak and Kamphaeng Phet.
• Minimum temperature: 23-28°C.
• Maximum temperature: 34-36°C.
• South-westerly winds: 10-20km/h.

Northeast

• Thunderstorms are forecast in 40% of the area, with heavy rain in some places.
• Affected provinces: Nong Khai, Bueng Kan, Sakon Nakhon and Nakhon Phanom.
• Minimum temperature: 24-26°C.
• Maximum temperature: 33-37°C.
• South-westerly winds: 10-20km/h.

Central region

• Thunderstorms are forecast in 60% of the area, with heavy rain in some places.
• Affected provinces: Nakhon Sawan, Uthai Thani, Kanchanaburi, Ratchaburi, Nakhon Pathom and Samut Sakhon.
• Minimum temperature: 24-27°C.
• Maximum temperature: 35-37°C.
• South-westerly winds: 10-20km/h.

East

• Thunderstorms are forecast in 60% of the area, with heavy to very heavy rain in some places.
• Affected provinces: Nakhon Nayok, Prachinburi, Chachoengsao, Chonburi, Chanthaburi and Trat.
• Minimum temperature: 24-28°C.
• Maximum temperature: 32-36°C.
• South-westerly winds: 20-35km/h.
• Wave heights are about 2 metres, rising above 2 metres in thunderstorms.

South (east coast)

• Thunderstorms are forecast in 60% of the area, with heavy rain in some places.
• Affected provinces: Chumphon and Surat Thani.
• Minimum temperature: 23-26°C.
• Maximum temperature: 33-36°C.
• From Surat Thani northwards: south-westerly winds of 20-35km/h.
• Wave heights are 1-2 metres, rising above 2 metres offshore and in thunderstorms.
• From Nakhon Si Thammarat southwards: south-westerly winds of 15-30km/h.
• Wave heights are about 1 metre, rising above 2 metres in thunderstorms.

South (west coast)

• Thunderstorms are forecast in 70% of the area, with heavy to very heavy rain in some places.
• Affected provinces: Ranong, Phang Nga, Phuket, Krabi, Trang and Satun.
• Minimum temperature: 23-24°C.
• Maximum temperature: 31-34°C.
• From Phang Nga northwards: south-westerly winds of 20-40km/h.
• Wave heights are 2-3 metres, rising above 3 metres in thunderstorms.
• From Phuket southwards: south-westerly winds of 20-35km/h.
• Wave heights are about 2 metres, rising above 2 metres in thunderstorms.

Bangkok and vicinity

• Thunderstorms are forecast in 70% of the area, with heavy rain in some places.
• Minimum temperature: 25-27°C.
• Maximum temperature: 34-36°C.
• South-westerly winds: 10-20km/h.