Bureau hazard preparedness and response east manager Jane Golding said 76 millimetres landed in Narrabri, on the North West Slopes, across Wednesday, describing it as “really the start of the rain event for that area”.
In one day, it was more than the town’s average monthly rainfall of 68mm for November.
“All of the ingredients are in place for thunderstorms over the next 24 to 48 hours,” Ms Golding said on Thursday. “In particular, for thunderstorms with very intense rainfall rates. Those conditions can lead to dangerous, life-threatening conditions.”
She said thunderstorms have an intense onset and typically last half an hour before they clear but can cause “really dangerous flash-flooding”.
The bureau is not expecting flooding in NSW to be as widespread as in March. Ms Golding said it was “hit-and-miss” and quite hard to predict the exact location of the intense rain.
A flood watch has been issued for catchments in the Northern and Central Tablelands and North West Slopes including moderate to major flooding on the Upper Macintyre River and minor to moderate flooding on the Namoi River.
As of Friday morning, minor flooding was reported at 10 river height stations across the state.
NSW State Emergency Service Deputy Commissioner Daniel Austin said the rescues had included when an empty school bus and a number of cars became trapped between two rapidly rising bodies of water outside Narrabri late on Wednesday.
“Those people stayed in place, they chose not to try and drive through those floodwaters, they called the emergency services and collectively, we worked together and got those people out,” he said.
A campground at Bingara on the Gwydir River, with about 15 caravans in the area, was evacuated after midnight.
“Those people were forced to move with the assistance of the emergency services, and we conducted about four flood rescues in that particular scenario,” Mr Austin said.
“This is a fast-moving event in places. The risk is not just from the long, slow rainfall, but it’s actually these sharp, short thunderstorms.”
Bureau meteorologist Jonathan How said south-east NSW, the ACT and Victoria will become a focus of rain and wind into Friday.
“Storms will continue along the eastern seaboard but begin to push offshore in the evening, mostly clearing by Saturday morning,” he said.
NSW Emergency Services Minister David Elliott said there were close to 200 calls made for assistance on Wednesday. The SES said about two thirds were storm-related and about 50 flood-related, including in metropolitan Sydney as heavy showers passed over.
A cold and windy air mass behind the system is expected to bring cool conditions towards the end of the weekend, including to the Western Plains where average temperatures of 25 to 30 degrees could drop into the mid-teens. Snow is also forecast at relatively low levels over the Southern Slopes.
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