New South Wales is bracing for a weekend of wild and wet weather, with possible flooding, after some areas had more than 100mm of rain over the past week

The Bureau of Meteorology says the Illawarra, Hunter, Central Coast and Greater Sydney regions can expect to get a similar triple-digit dumping over Saturday night and Sunday.

They say they can see some pretty major impacts, areas of flooding, blocked drains, closed roads, causing big traffic.

The Sydney Half Marathon is set to go ahead on Sunday despite the conditions, with more than 19,500 runners registered.