"We expect rain to develop in the afternoon and there is a change that there may be some heavy and thundery falls on Saturday afternoon as well."
Last year's festival attracted around 40,000 people and at popular times there can be more than 20,000 people in the central city, with over 300 events across five days at this year's festival.
Overnight temperatures on Saturday will hit a low of 14C, thanks to a front passing over bringing in a south-west change.
Temperatures will be "much cooler" of Sunday, with a high of 22C and a low of 13C.
"On Sunday, we are looking at some cloudy periods with a few showers," Best said. "The showers are expected to clear throughout the course of the evening however, with southerlies throughout the day."
As the vintage car parades, fashions shows, outdoor concerts, dining experiences and more come to a close on Monday, temperatures will remain lower.
"Monday will be partly cloudy conditions with some light winds," Best said.
"Temperatures will be around 21 degrees maximum, with a minimum of 13 degrees."