Heaviest rain in years forecast across the Illawarra this weekend

Starting on Friday, the Bureau of Meterology has predicted a more than 90 per cent chance of rain for the region through to Monday, with falls of up to 60 and 80 mm possible on those days.

If the maximum predicted rainfall occurs, the region would get 210mm across the four days - the highest monthly total since March 2017.

That month, the region flooded with multiple consecutive days of rain, which caused havoc on roads, and in parks, sports grounds and homes.

At the Bellambi weather station on March 17, 2017, 75mm was recorded, while Albion Park received 151mm that same day.

There was a slight wet patch last March, when there were nine consecutive days of rain and more than 20 mm fell at Bellambi for four days straight.

BOM meteorologist David Wilke said it was not unreasonable to compare this week's forecast to that of Mark 2017.

"In terms of the rainfall forecast, it's not out of the question," he said.

"It's certainly a significant rainfall event. This kind of widespread rain - a deep coastal trough - is something we haven't seen in a while and it's looking like it will be a multi-day event, starting [on Thursday] and continuing for a week.

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"We should be looking at somewhere between 100 to 200mm over the four days [from Friday to Monday] but, a few days out, it's hard to tell exactly how it will play out."

The rain is expected to hit most of Australia's east coast, between Rockhampton and East Gippsland, and will help to extinguish many of the fires still burning in Queensland, NSW and Victoria.

However, it will also bring an increase in the risk of flash flooding in many areas.

Mr Wilke said rain runoff could respond differently when falling on very dry soil, or in bushfire affected terrain. However, he said the small amount of rain which has soaked into the ground in recent weeks may help to protect some areas in the Illawarra from the increased risk of flooding.

"This rain is good for going fires, but there are some risks people need to be aware of in those areas," he said.