The severity of a storm cell that dumped 166.8mm of rain on Dungog within two hours could not have been predicted, a court has heard.
Representatives from the Bureau of Meteorology gave evidence on the third day of an inquest into three deaths that occurred during the 2015 superstorm.
Colin Webb, 79, Brian Wilson, 72, and Robin Macdonald, 68, died at their homes - within a street of each other - in Dungog during the natural disaster on the morning of April 21.
The court heard on Wednesday that a blanket of rainfall reached from Penrith to Taree during the weather event.
BoM state and territory manager for NSW/ACT Ann Farrell said the superstorm was "a broad scale event".
The court heard that a complex weather system with intense rain appeared over Dungog at about 5am, before major flooding occurred in the town.
“Very strong, destructive winds were recorded with this event as well as intense, widespread rainfall,” Ms Farrell said.
She showed the court data that confirmed the most intense rainfall hit Dungog within about an hour of when Mr Webb, Ms Macdonald and Mr Wilson were found dead.
Bureau of Meteorology experts giving evidence: storm was "broad scale event" @newcastleherald— Nick Bielby (@nickbielby) August 30, 2017
According to measurements taken at Dungog Post Office, 116.4mm of rain fell between 5am and 6am and 50.4mm fell between 6am and 7am.
When Mark Cahill – the Counsel Assisting Deputy State Coroner Teresa O’Sullivan – asked Ms Farrell if there were any “telltale signs” of what was about to occur before the cell developed over Dungog, she replied: "No".
"Were there clues looking at the radar that this was about to happen? The answer to that is no," she said.
The BoM released a Flood Watch notice at about 9am on April 20, which said there was more than a 70 per cent chance of minor to moderate flooding of the Paterson and Williams rivers.
A Flood Watch was described to the court as “a heads up” to agencies like the SES – which was briefed at 11am on April 20 – and is different to a BoM Flood Warning.
The bureau issued Flood Warnings about 11.50pm on April 20 and about 3am on April 21.
BoM flood expert Jeff Perkins said modeling for weather systems was initially based on forecasts and there was a degree of uncertainty.
But, he said, as the bureau put recorded rainfall into its modelling during the given weather event, that uncertainty would decrease.
“There’s no magic bullet for flood warnings,” Mr Perkins said.
“Flood forecasting is about limiting the uncertainty as [you] go through the event and provide the best possible advice.”
On Wednesday afternoon, the court heard about the development of the draft Flood Risk Management Study and Plan for Dungog, which was placed on public exhibition earlier this year.
The document is aimed at improving the town’s flood response.
The inquest, before Deputy State Coroner Teresa O'Sullivan at Newcastle Courthouse, continues on Thursday.
More SES representatives are expected to take the witness stand before final submissions are made.