Large parts of eastern Australia can expect a week of significant rainfall.
For tropical Queensland, this will be a continuation of recent wet weather, while for areas south of the tropics along the coast and adjacent ranges, it will mark a break in the pattern of relatively dry weather.
The rain that is currently falling, or that is due to fall, can be broadly separated into three distinct events.
Ongoing rainfall from ex-Tropical Cyclone Koji drifts south
Extremely heavy rain has fallen over the past day or two in Queensland's Central Coast and Whitsundays forecast district (centred around Mackay) with heavy rainfall extending to the Central Highlands and Coalfields district, as well as adjacent inland areas.
To 9am Monday, some of the notable 24-hour rainfall totals included:
216.5mm at Clermont Bridge and 203.2mm at nearby Clermont Airport. This daily total is more than double the monthly average for a town located some four hours inland from Rockhampton.
218mm at St Lawrence in the Capricornia forecast district.
150.2mm at Mackay Airport after 77.2mm the previous day.
"We are seeing heavy rainfall in places like Emerald and Rockhampton this Monday due to the monsoonal flow wrapping around the low pressure system formed by ex-Tropical Cyclone Koji," Weatherzone metrologist Joel Pippard explains.
Heavy rain is likely to continue pushing southwards, reaching Brisbane by Tuesday, as monsoonal winds converge with easterlies and an upper level trough.
Onshore winds to soak NSW in second half of week
Parts of the NSW coastline, including Sydney, are seeing drizzly rain this Monday, but heavier rain can be expected from Thursday into the weekend as a low forms near the NSW coast.
Persistent easterly winds and abundant atmospheric moisture should ensure that Sydney gets its first decent soaking of the summer, after a very dry December with just 19mm in total (monthly average 77.7mm) and modest January rainfall totals to date.
Widespread thunderstorms likely on Thursday
A significant thunderstorm outbreak potentially covering most of Queensland and virtually the entire eastern half of NSW is on the cards for Thursday.
According to Weatherzone meteorologist Joel Pippard, all the ingredients for thunderstorm development should be in place, with plenty of moisture and atmospheric instability as a pool of cold upper air pushes north.
Thursday will also be hot inland, with temperatures approaching 40°C in places like Dubbo, which means that NSW storms will likely develop in forecast districts like the Central West and North West Slopes and Plains – hundreds of kilometres west of the coast and adjacent ranges.
Will there be rain relief for Victoria?
Image: Predicted rainfall for SE Australia for the week ending Sunday, January 18, according to the ECMWF model.
It’s difficult at this stage to predict how much of the eastern Australian rain due from midweek onwards will make its way south and east to Victoria.
While Victoria’s East Gippsland region can expect significant totals around 20mm later this week, early indications are that only lighter falls in the range of 10mm or less will make it to some of the worst fire-affected areas in central, western and northeastern Victoria.