SINGAPORE - Moderate to heavy showers and possibly even flash floods are on the cards over the coming weeks with the onset of the northeast monsoon season, the Meteorological Service Singapore (MSS) warned on Tuesday.

The first half of November has already been wetter than usual in many parts of the island, with 188mm of rainfall recorded at Changi climate station, the MSS said.

This year, rainfall for November and December - typically the months with the most rain - is expected to be about 20 per cent above the long-term average of 256.6mm and 288.4mm respectively.

Typically lasting from late November to January, the season is expected to cause between two and four monsoon surges. These usually bring periods of prolonged widespread moderate to heavy rain lasting between two and five days, occasionally windy conditions, and cooler temperatures.

A monsoon surge refers to the steady strengthening of north-easterly winds blowing from the South China Sea.

In addition to the regular weather forecast, the MSS will issue warnings when heavy rain or prolonged monsoon rain is expected.

"This will help the public to better prepare for heavy rain," it said in an advisory. "Heavy rain coinciding with high tides could lead to localised flash floods in low-lying areas."

National water agency the PUB is also working with the National Environment Agency's Department of Public Cleanliness to ensure that drains remain free-flowing.

PUB officers will also inspect 100 major construction worksites to ensure that nearby drains are free of debris.

They will also monitor 171 water level sensors installed in major drains and canals as well as 161 CCTV cameras that monitor road conditions in low lying areas and other hotspots.