Thundershowers are forecast for all regions with isolated heavy rains in some areas.
Waves 1-2 metres high and more than two metres high during thundershowers are expected in the Andaman Sea and upper Gulf of Thailand.
All ships should proceed with caution during thundershowers, the department said.
The weather forecast for the next 24 hours:
North: Thundershowers in 60 per cent of the areas with isolated heavy rains; temperature lows of 24-26 degrees Celsius, highs of 30-36°C.
Northeast: Thundershowers in 60 per cent of the areas with isolated heavy rains; temperature lows of 23-26°C, highs of 31-35°C.
Central: Thundershowers in 60 per cent of the areas with isolated heavy rains; temperature lows of 24-26°C, highs of 33-37°C.
East: Thundershowers in 60 per cent of the areas with isolated heavy rains; temperature lows of 24-28°C, highs of 30-35°C; waves a metre high and 1-2 metres during thundershowers.
South (east coast): Thundershowers in 60 per cent of the areas with isolated heavy rains; temperature lows of 24-25°C, highs of 32-34°C; waves a metre high and 1-2 metres during thundershowers.
South (west coast): Thundershowers in 60 per cent of the areas with isolated heavy rains; temperature lows of 21-25°C, highs of 29-33°C; waves 1-2 metres high and over two metres during thundershowers.
Bangkok and surrounding areas: Thundershowers in 60 per cent of the areas; temperature lows of 26-27°C, highs of 33-36°C.