If current projections play out, 3600 residential properties will be affected in Brisbane and of those, 2100 are unit dwellings where only ground floor flooding is expected.
Queensland Premier Campbell Newman says flood peaks would be much less than what was experienced in 2011.
Brisbane is expecting a 2.6 metre flood peak, nearly half of the 4.46m peak in 2011.
The Ipswich peak is expected to be five metres less than the 19.4m level in 2011.
"There will be flooding but the flooding is much much lower than what we saw in 2011," he said.
Mr Newman said the projections were based on the best scientific modelling by forecasters.
"The peak of any flood will occur in Ipswich we believe around midnight (AEST) tomorrow (Monday) night," Mr Newman said.
"Similarly the peak at the western side of the Brisbane City Council boundary will be about midnight on Monday night."
Moggill is projected to be the first Brisbane suburb to be flood-affected on Monday afternoon.
The worst of the projected flooding would be seen further downstream around noon on Tuesday, with another peak expected at noon on Wednesday.
"If it doesn't occur, then I'm sorry in advance," the premier said.
He urged people not to panic, but to check the flood maps and to prepare if they were in an area that may flood.
However rainfalls are easing in the Brisbane and Stanley river catchments, which flow into Wivenhoe and Somerset dams.