It's sunny in Brisbane, so why is a wall of water coming?

Castlemaine Street in the suburb of Milton is flooded in Brisbane, Australia. Photo / Getty Images

Many parts of Brisbane continue to go underwater this afternoon even though sunnier conditions have moved in. Despite the forecast for much drier weather in the city over the next 48 hours, the flood waters are only going to get worse.

WeatherWatch.co.nz head weather analyst Philip Duncan says the flooding in Brisbane is quite different to the flooding in Toowoomba yesterday.

"The flooding in Toowoomba was a result of a localised down burst in the area. A huge volume of rain fell over a small area in a short time - which is why we saw streams turning into raging rivers in a matter of minutes".

Mr Duncan says Brisbane is facing a different flood altogether.

"What Brisbane is being hit by is heavy rain that fell upstream over the past five days, and in particular the past 48 hours. The Wivenhoe Dam blocks the Brisbane River about 80km west of Brisbane and it is massive rainfall in this catchment that is causing the delayed flooding in Brisbane."

Figures by the Bureau of Meteorology show an incredible amount of rain has fallen around the lake.

"Well over 100mm of rain had already fallen around the lake since Friday, but yesterday an incredible further 249mm fell in just 24 hours. This wall of water is now being released by the dam and is heading towards Brisbane," says Mr Duncan.

A total of 370mm of rain has fallen in the area in just five days.

Brisbane itself has received much less - but has still received a significant amount. On Monday the city recorded 111mm in just 24 hours, which may be a record breaker for Janury.

Up until 12pm NZT Brisbane had recorded a total of 270.8mm of rain - the average for January is 101.5mm.

- NZHERALD STAFF