Heavy rain and moderate to rough sea conditions are expected to lash Singapore between now and Sunday.
The National Environment Agency (NEA) has also said in an advisory that flash floods may also occur in low-lying areas early in the afternoon if the rain coincides with predicted high tides.
The advisory was issued as Singapore came within half a degree of recording its lowest ever December temperature at 10pm on Wednesday, when parts of the island registered 21.1 deg C.
The coldest on record was Dec 2, 1964, when it fell to 20.6 deg C. Between 2008 and last year, the lowest December temperature ranged from 22.1 to 23.2 deg C.
This month may be the wettest December in recent years, with the NEA predicting up to 30 per cent more rainfall than the long-term average of about 288mm for the month.
The island's north-east has been the most drenched so far.
By Tuesday, the wettest areas had received up to 98 per cent of the long-term average rainfall for the month.
The driest parts were in the south and west, where only 30 per cent to 40 per cent of the long-term average rainfall were recorded in that time.
Singapore is in the middle of the north-east monsoon season's wet phase, which typically occurs between mid-November and January.
Some heavy rain is forecast for the weekend due to an expected monsoon surge, which occurs when winds over the South China Sea grow stronger, resulting in prolonged heavy rain.
The Meteorological Services Singapore has said that its weather models forecast a slightly more active monsoon season, with possibly more thunderstorms and monsoon surges.
Outdoor enthusiasts should be careful this weekend.
Moderate to strong winds as well as moderate to rough sea conditions are expected during monsoon surges.
The meteorological service has also predicted high tides of about 3m between 12.20pm and 1.30pm from today to Sunday.
Separately, national water agency PUB yesterday urged people to report flash floods through its Facebook or Twitter channels, or by calling its 24-hour call centre on 1800-284-6600.
No registration is needed for the online platforms and the tip-offs should include details such as the location, time and if possible, an image of the incident.
PUB said this would complement its extensive system of water-level sensors and closed-circuit television cameras around Singapore to monitor the situation.