The Bureau of Meteorology says winds to 75kmh in strength and more than 200mm of rain in places would impact the region with increasing rain likely to be evident from later today.
Strong winds offshore are also expected to generate huge, confused seas which will batter the coast line and result in a small surge above the Highest Astronomical Tide measure for Sunshine Coast beaches.
Sunshine Coast Council Disaster Management leader John Gallina said there was concern for high locations which would be vulnerable to strong winds and low-lying foreshore locations.
"This one is a big system," he said.
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Latest modelling is predicting the south east corner's heaviest falls will concentrate over the Sunshine Coast with some areas likely to receive in excess of 300mm.
SES teams are preparing sandbags and residents have been urged to secure loose objects, clear any blocked drains and gutters and to ensure they have emergency supplies of water, food and batteries.
BOM forecaster David Crock said the peak of the system's impact was coming early to the south east as the tropical low sped up as it passed through the central highlands on a track which will bring it into south east Queensland.
"On Friday we are expecting it to clear away to Brisbane and the Gold Coast and then out to sea," Mr Crock said.
"There's going to be a lot of rain with wide spread falls between 50mm and 150mm and there will be areas where it is 200mm plus.
The Sunshine Coast hinterland appears particularly vulnerable with falls of up to 400mm in the Upper Mary River.
"We are expecting heavy rain starting today and continuing through to Saturday," Mr Gallina said.
"There will localised flooding in low-lying areas and there will be wind but not at cyclonic strength. The key message is 'be prepared'."
Mr Gallina said disaster planners had been re-assured by the BOM that the ex-Cyclone Debbie system would not reform once it passes back out to sea on Saturday.
Noosa Local Disaster Management Centre co-ordinator Alan Rogers said the Sunshine Coast was now in the path of a very big weather system.
"I can see water, I'm expecting a lot of water from this one," Mr Rogers said.
How much damage it causes will depend, he said, on how long the system hung around.
"If it is just six hours that's not so bad," he said. "If it's 24 hours that's another matter.
"We go to lean forward (state of alert) this afternoon. We are fully engaged."
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