Summer is expected to start with a cold snap in south-east Queensland, with below-average temperatures forecast for later this week.
Bureau of Meteorology senior forecaster Felim Hanniffy said it would be a very cool start to the season, with Brisbane temperatures "struggling into the low twenties" by Thursday.
"The normal average maximum temperature for December in Brisbane City is around the 30-degree mark, so seven or eight degrees below average," he said.
"Some areas you're talking 10 or even double digits below, given the extensive cloud cover about the south-east."
Those below average temperatures are expected to be joined by thick cloud, persistent rain and south-easterly winds, a stark contrast to recent conditions that saw Brisbane temperatures into the low and mid-thirties.
Mr Hanniffy said while the coolest days will be Wednesday and Thursday, the south-easterly winds will mean mild conditions should last into early next week.
"Temperatures [will be] slowly coming back as that cloud starts to thin out, but still below average for the time of year with daytime maximum temperatures around 24 and 25 degrees around much of the south-east come the weekend."
Why the cool change?
A low-pressure system is expected to form near the central coast by the middle of the week.
"This looks to enhance rainfall across this stretch of coast, particularly central parts and along the coast between Bundaberg and Mackay," Mr Hanniffy said.
The low is expected to then move south towards Fraser Island before moving off the south-east coast during Thursday and Friday.
Mr Hanniffy said it's that system, combined with the south-easterly winds, that's causing the cooler weather.
"A ridge to the west is going to generate quite a blustery and cool south-easterly air flow up along the south-east, and that's going to stick around through the weekend and into next week as well."
Monsoon-like conditions possible for the far north
Further north can also expect a wet start to the season as two climate drivers are at play.
The combination of a Madden-Julian Oscillation (MJO), which moves from west to east across the equator, and an Equatorial Rossby Wave could trigger monsoon like conditions.
"Normally the MJO on its own is enough to ramp-up activity up in the far north, but when you've got two drivers like that, that's kind of like a double whammy, a tag team in a way and increases that activity," Mr Hanniffy said.
There remains a great deal of uncertainty about how those conditions will eventuate.
"There is potential for lows to formulate in the Gulf of Carpentaria and then potential for that low to move across the peninsula and into the north Coral Sea later in the weekend," Mr Hanniffy said.
