Meanwhile, tropical depression "Dianmu" has downgraded to an active low-pressure cell over Khon Kaen province.
Abundant rains with isolated heavy to very heavy rains and strong winds are forecast for the North, the Northeast, the Central including Bangkok and its vicinity, and the East regions.
People in risky areas should beware of overflows and flash floods, the department said. Waves in the Andaman Sea and the Gulf of Thailand are about 1-2 metres high and over two metres high in thundershowers. All ships should proceed with caution and keep off thundershowers, the department said.
The weather forecast for the next 24 hours:
North: Thundershowers in 80 per cent of the areas with isolated heavy to very heavy rains; temperature lows of 23-24 degrees Celsius, highs of 30-34°C.
Northeast: Thundershowers in 80 per cent of the areas with isolated heavy to very heavy rains and strong winds; temperature lows of 23-24°C, highs of 26-29°C.
Central: Thundershowers in 80 per cent of the areas with isolated heavy to very heavy rains; temperature lows of 23-25°C, highs of 29-33°C.
East: Thundershowers in 80 per cent of the areas with isolated heavy to very heavy rains; temperature lows of 23-25°C, highs of 27-31°C; waves two metres high and over two metres during thundershowers.
South (east coast): Thundershowers in 40 per cent of the areas; temperature lows of 23-24°C, highs of 31-35°C; waves 1-2 metres high and two metres during thundershowers.
South (west coast): Thundershowers in 60 per cent of the areas with isolated heavy rains; temperature lows of 19-25°C, highs of 30-33°C; waves 1-2 metres high and over two metres during thundershowers.
Bangkok and surrounding areas: Thundershowers in 80 per cent of the areas with isolated heavy rains; temperature lows of 24-26°C, highs of 29-31°C.