This month could be the wettest December here in several years. The amount of rain recorded for the first four days of this month is already about half that seen for the full month in 2011 and last year.
About 164mm of rain came down between Sunday and Wednesday, compared with about 285mm for December 2011 and 363mm for December last year.
The heaviest rainfall ever recorded for December was 766mm in 2006.
The Meteorological Service Singapore (MSS) predicted in October that the rainfall for this month and next could exceed the long-term averages of about 298mm for December and 243mm for January by up to 20 per cent.
Weather models forecast a slightly more active north-east monsoon season, with possibly more thunderstorms and monsoon surges.
The season's wet phase typically occurs between mid-November and January. A monsoon surge occurs when winds over the South China Sea grow stronger during the season, resulting in prolonged heavy rain.
The National Environment Agency (NEA) said on its website that short, thundery showers are expected on six to eight days in the first half of this month, and that periods of moderate to heavy rain are likely on two to three days over this period.
Asked if Singapore might experience the type of flooding seen recently in Malaysia, MSS said heavy rain from the latest monsoon surge affected mostly the eastern coastal states of Peninsular Malaysia. "Singapore was less affected," it said.
However, the NEA said in a monsoon update on its website on Tuesday that people should not take the weather lightly.
"When a monsoon surge is affecting the region, moderate to strong winds can be expected, in particular over sea areas. Moderate to rough sea conditions can also be expected. Outdoor enthusiasts should take necessary precautions when out at sea," it said.
Mr Richard Tan, president of the Singapore Life Saving Society, said that even during normal weather, currents in the sea could carry people very far from shore and make it difficult for them to swim back to land.
He recommended that people leave the water immediately when weather and sea conditions turn rough. Swimmers who insist on continuing should not swim alone. They should also make sure there is a lifeguard on duty.