In the space of just a few hours, two weather systems combined to dump more than 200 millimetres of rain on parts of the region during the late afternoon.

The SES responded to 34 flood rescues and received 456 general calls for help across its Illawarra/South Coast region during the 24 hours to Friday morning. 

“All those flood rescues were conducted in a three-hour period [on Thursday]… so it [the rain] caught us off-guard in that sense, it was just so intense,” SES spokeswoman Terri Langendam said.

Most of the SES call-outs were for leaking roofs, flash flooding and sandbagging.

Two adults and a child were rescued from a tree after becoming stranded while checking livestock near Nowra. 

Fallen trees blocked the paths of two freight trains on the Moss Vale Line at Unanderra, while a passenger train became stuck on the South Coast Line between Albion Park and Dapto. 

A map of SES flood rescues showed suburbs at the base of the escarpment, from Figtree to Albion Park, were the worst-affected by the deluge.

At 2pm on Thursday, Wollongong’s Albion Park weather station had received just 2.4mm of rain. By 5pm, that figure was 109.2mm.

In total, the inland suburb was drenched by 151.4mm in the 24 hours to 9am on Friday.

Falls were even heavier on the escarpment, with 24-hour totals of 207mm at Macquarie Pass, 203mm at Robertson, 202mm at Clover Hill and 197mm at Upper Calderwood. 

On the coast, 75mm was tipped out of the rain gauge at Bellambi. 

Bureau of Meteorology forecaster Gabrielle Woodhouse said the extreme weather was the result of a lingering coastal trough combining with a strong cold front that crossed southern parts of NSW late afternoon.

“We had some fairly strong onshore [wind] flows and a high level of moisture, so that meant we had some rather heavy showers with some thunderstorms,” she said. 

Earlier forecasts had predicted storms, but didn’t suggest the intense nature of the rainfall. The bureau wasn’t caught off-guard, she said, adding a severe thunderstorm warning was issued.

“In this kind of situation, we know that there is a lot of moisture throughout the atmosphere and that all we need is a really strong trigger to trigger those thunderstorms,” she said.

“Generally, I think we were looking at a little bit further north for some of that thunderstorm activity, although it wasn’t ruled out further south. 

“It was just a matter of waiting and seeing ... how that cold front interacted with the trough and that’s when we started to see the rainfall really ramp up with those thunderstorms.”