More than 120mm of rain is expected to fall across three days later this week with torrential conditions forecast.
The Bureau of Meteorology (BOM) says up to 25mm of rain could fall in Penrith on Thursday, up to 70mm on Friday and up to 30mm on Saturday.
It will also coincide with a significant temperature drop with 22 degrees predicted on Thursday and Friday and 25 on Saturday.
The wild weather is set to spark chaos for Round 5 of the NRL with three games scheduled in Sydney across Friday and Saturday, including Manly up against Penrith at Brookvale on Saturday evening.
Races are also scheduled to run in Hawkesbury on Saturday while the Wanderers are due to play Brisbane at CommBank Stadium on Friday night.
