KEEP your umbrellas close - it is going to be a wet, windy countdown to Christmas, says the weatherman.

Thunder and showers are expected over the next three days, particularly in the afternoons, and moist and unstable monsoon winds will continue to blow for the rest of the month.

That means cool days and more rain than normal.

Rainfall for the second half of the month is expected to be 'substantially above the average', said a National Environment Agency spokesman.

It is hard to say if it will beat last December's record of 765.9mm, but the month so far has been wetter than usual.

Rainfall was well above average in the first two weeks of December, particularly on Dec 5 and Dec 10, when more than 100mm of rain fell in some areas.

The eastern part of the island, which is most exposed to the monsoon, has been most badly bombarded. Rainfall recording stations in Changi got between 330 mm and 360 mm of rain, up to three times more than average.

But the water is not just going to come from above. High tides are also expected from Sunday to next Friday, with a high of between 3m and 3.2m each day.

If they coincide with heavy rain, it could mean flash floods in low lying areas, the NEA warned. This, despite a move by national water agency PUB earlier this month to put flood alleviation projects into high hear.

Flood-prone areas include Chinatown and the Central Business District, Tanjong Katong, Geyland, Lorong Buangkok and the area off Jalan Besar.

About 100 PUB staff and contractors have been put on high alert. They are checking for blockages in drains in an attempt to ensure water can flow out of flooded areas, the agency said.

The rainy season, brought in by the Northeast Monsoon, lasts till January.

The public can get the latest weather reports and flood alerts by calling the NEA on 6542-7788 or PUB-ONE on 1800-284-6600, or at www.nea.gov.sg