The department said the monsoon trough lies across the North, the Central, and the lower Northeast while the moderate southwest monsoon prevails over the Andaman Sea, Thailand and the Gulf.
People in the risky areas should beware of severe conditions that may cause flash floods and water runoffs, the department cautioned.
The weather forecast for the next 24 hours:
North: Mostly cloudy with thundershowers in 60 per cent of the areas and isolated heavy rain; temperature lows of 24-26 degrees Celsius and highs of 32-35°C.
Northeast: Mostly cloudy with thundershowers in 60 per cent of the areas and isolated heavy rain; temperature lows of 24-25°C and highs of 33-34°C.
Central: Mostly cloudy with thundershowers in 70 per cent of the areas and isolated heavy rain; temperature lows of 24-26°C, highs of 34-35°C.
East: Cloudy with thundershowers in 80 per cent of the areas and isolated heavy to very heavy rain; temperature lows of 23-26°C, highs of 29-33°C; waves a metre high and 1-2 metres during thundershowers.
South (east coast): Mostly cloudy with thundershowers in 60 per cent of the areas and isolated heavy rain; temperature lows of 24-25°C, highs of 32-33°C; waves 1-2 metres high and over 2 metres during thundershowers.
South (west coast): Mostly cloudy with thundershowers in 70 per cent of the areas and isolated heavy rain; temperature lows of 23-25°C, highs of 30-33°C; waves 1-2 metres high and over 2 metres during thundershowers.
Bangkok and surrounding areas: Mostly cloudy with thundershowers in 60 per cent of the areas and isolated heavy rain; temperature lows of 24-26°C, highs of 34-35°C.