DELUGE

Wettest November on record: What's behind the rainy weather in Singapore?

- Angelica Ang

As the saying goes, "when it rains, it pours" - and that has literally been the case for Singapore in the past few weeks.

With a total rainfall of 419mm, November surpassed the previous record of 390.1mm set in the same month in 1992, the agency said. This represents an increase of 47.4 per cent from the average November rainfall of 284.3mm in previous years.

Thundery showers fell on most afternoons in the second half of November, with record rainfall on Nov 22 triggering flash floods in Yishun and Potong Pasir.

National water agency PUB said that 127.7mm of rain was recorded between 2.15pm and 4.50pm in northern Singapore that day.

The Straits Times spoke with the MSS to examine the science behind the monsoons, and other rain-making phenomena in Singapore.

WHAT ARE MONSOONS?

Monsoons are seasonal wind patterns that span a large geographic area, playing a significant role in influencing rainfall across regions throughout the year. They involve shifts in the direction of prevailing winds, which may blow moist air towards or away from land, thus affecting rainfall over it.

In Singapore, two main monsoon seasons shape the weather: The north-east monsoon, typically from December to March, and the south-west monsoon, from June to September. Both are part of the larger Asia-Australia monsoon, which impacts weather patterns across the globe.

During the north-east monsoon, Singapore experiences heavy rainfall and cooler temperatures, while the south-west monsoon brings comparatively drier and hotter weather.

WHY DOES THE NORTH-EAST MONSOON BRING RAIN?

The north-east monsoon occurs in two phases: the wet phase, typically from December to January, and the dry phase, from February to early March.

During the wet phase, winds approach from the north-east, and blow towards the south-west.