Weatherzone meteorologist Rob Sharpe said thunderstorms expected in Canberra Thursday afternoon signalled a pattern of showers and storms continuing until mid-next week.

He said the warm but wet weather on the way was the result of a high pressure system likely to move east of Tasmania by Friday before hovering around the NSW coast, plus a low-pressure trough travelling across the mainland towards the territory.

"Those troughs are providing instability for the ACT," Mr Sharpe said.

"That high pressure system is going to be sitting off the NSW coast into next week.

"We will see quite warm and humid weather. But it will really peak on Sunday with 30 degrees expected."

Mr Sharpe said Canberrans should expect rain and potential thunderstorms during the three days of festivities in the city.

The 2015 National Multicultural Festival will transform Civic into a kaleidoscope of colours, sounds and flavours from Friday to Sunday alongside Canberra's Fringe Festival, which new director Chenoeh Miller will try to distance from last year's burlesque controversy involving a dancer dressed as Hitler.

The forecast weather mirrors above-average humidity last month which lead to Canberra's wettest January in 16 years, with almost 100 millimetres of rain dousing the capital.

But daily rainfalls over the next few days aren't expected to top five millimetres.

Friday and Saturday are forecast to reach 26 degrees with minimums of 14 to 15 degrees.

Mr Sharpe said minimum temperatures would stay in the mid-teens until about Wednesday next week.

"Most days will be in the mid to high 20s. The hottest days will be Sunday and Wednesday - both days will likely nudge into the low 30s," he said.

"Most days we'll see showers and thunderstorms at least somewhere in the ACT. Through the weekend and into next week we will see this weather remaining."