Rainfall records set to tumble as storm heads south - Sydney Morning Herald

A slew of January rainfall records are likely to have been broken as the remnants of ex-tropical cyclone Oswald heads south along the NSW coast.

The weather bureau is still assessing the quality of the data collected for the 24 hours to 9am on Tuesday, but initial numbers point to Crystal Creek on the mid-north coast's Bellinger River as recording the highest rainfall total of 288 millimetres.

Sydney's Observatory Hill recorded 95 millimetres of rain for the period, the highest level since last March's severe rainstorms. In the Sydney region, the north shore's French's Forest and Castle Cove both saw 161 millimetres land in their rain gauges.

The Upper Rous River probably saw the state's heaviest falls from the storm, with 944 millimetres landing in the border zone site near Queensland in the past three days.

“It's not far short of a metre of rain,” said Aaron Coutts-Smith, NSW manager of climate services at the weather bureau. “When you think of those volumes, it's no wonder there has been flooding.”

That tally, though, fell short of the state's record over three days – 1090 millimetres recorded in December 1975 at Bowraville – Dr Coutts-Smith said.

“We've probably seen the heaviest falls from this system,” he said.

The storm's slow speed rather than the initial strength of tropical cyclone Oswald was the main factor in the unusually heavy rainfalls over so wide a region.

“It's uncommon but not unprecedented,” Dr Coutts-Smith said.

The highest rainfalls from the storm were in Queensland, at Boolaroo, about 780 kilometres north-west of Brisbane, with 1360 millimetres recorded in the three days to 9am on Sunday, he said.