People should beware of the severe conditions that may cause flash floods. Waves in the Gulf are expected to rise 2-3 metres high and above three metres during thundershowers. All ships should proceed with caution and keep off thundershowers, while small boats should keep ashore until December 26, the department said.
Meanwhile, the high-pressure system covering upper Thailand is weakening, increasing temperatures by 1-2 degrees Celsius, with fog in the morning. Mountaintops remain cold to very cold with frost in some areas.
The weather forecast for the next 24 hours:
North: Cold to cool weather with light fog in the morning; minimum temperature 10-19°C, maximum 27-34°C; temperature on hilltops is likely to drop to 2-10°C with frost in some areas.
Northeast: Cold to cool weather with light fog in the morning and isolated light rain; minimum temperature 15-20°C, maximum 29-33°C; temperature on hilltops is likely to drop to 6-14°C.
Central: Cool weather with light fog in the morning and isolated light rain; minimum temperature 18-23°C, maximum 31-34°C.
East: Cool weather with light fog in the morning and isolated light rain; minimum temperature 20-25°C, maximum 31-34°C; waves 1-2 metres high and two metres off shore.
South (east coast): Mostly cloudy with thundershowers in 60 per cent of the areas and isolated heavy rain; minimum temperature 22-25°C, maximum 27-30°C; waves 2-3 metres high and over three metres during thundershowers.
South (west coast): Mostly cloudy with thundershowers in 40 per cent of the areas and isolated heavy rain; minimum temperature 22-23°C, maximum 29-31°C; waves 1-2 metemres high and two metres during thundershowers.
Bangkok and surrounding areas: Light fog in the morning with isolated light rain; minimum temperature 23-24°C, maximum 32-34°C.