Continuous rainfall and isolated heavy rain are forecast for the North, the Central, the East and the South.
People in risky areas should beware of severe conditions, the department said. Waves in the Andaman Sea and the Gulf are likely to rise more than two metres high during thundershowers. All ships should proceed with caution and keep off thundershowers, the department advised.
The weather forecast for the next 24 hours:
North: Mostly cloudy with thundershowers in 60 per cent of the areas; minimum temperature 24-25 degrees Celsius, maximum 33-35°C.
Northeast: Mostly cloudy with thundershowers in 60 per cent of the areas; minimum temperature 23-25°C, maximum 33-34°C.
Central: Cloudy with thundershowers in 60 per cent of the areas and isolated heavy rain; minimum temperature 23-25°C, maximum 32-34°C.
East: Cloudy with thundershowers in 60 per cent of the areas and isolated heavy rain; minimum temperature 23-25°C, maximum 31-34°C; waves 1-2 metres high and over two metres during thundershowers.
South (east coast): Mostly cloudy with thundershowers in 60 per cent of the areas; minimum temperature 23-25°C, maximum 31-34°C; waves a metre high and 1-2 metres during thundershowers.
South (west coast): Mostly cloudy with thundershowers in 60 per cent of the areas; minimum temperature 22-25°C, maximum 30-33°C; waves 1-2 metres high and over two metres during thundershowers.
Bangkok and surrounding areas: Mostly cloudy with thundershowers in 60 per cent of the areas and isolated heavy rain; minimum temperature 24-25°C, maximum 32-34°C.