SINGAPORE - An uncharacteristic chill has descended on Singapore, with temperatures across parts of the island dipping to a low of 22.8 deg C on Wednesday (Jan 10).

The National Environment Agency (NEA) said this was due to a monsoon surge in the South China Sea and surrounding region, and it has forecast cooler days ahead.

Monsoon surges bring cool air and thunderstorms to Singapore. But this weather phenomenon is not uncommon here.

Singapore experiences between two and four monsoon surges each year on average, occurring mostly between the months of December and March, said the NEA on its website. Each monsoon surge can last between one and five days, during which widespread continuous moderate to heavy rain will affect the island, added the agency.

The northern hemisphere experiences winter from December to March, a period marked by dry and cool air.

Monsoon surges occur when a sudden increase in wind speed causes the cold air to surge southwards into the South China Sea.

As the cold air moves south, it warms and gathers moisture, resulting in dense rain clouds being formed over the equatorial region, including in Singapore.

Assistant Professor Winston Chow, a weather researcher from the National University of Singapore's geography department, said that cold temperatures are usually linked to rain, and storms can result in exceptionally low temperatures, independent of season.

"However, the cool mean temperatures typically experienced in December and January are usually associated with monsoon surges," he said.