A major rain and storm event intensifying across south-east Australia could trigger flooding during the next 48 hours.
uncertain
event → intensify → hours
The sudden soaking follows a severe lack of rain in September — Melbourne only picked up 18mm last month, but was soaked by 20mm in just one hour on Thursday afternoon.
And for many areas, even heavier rain is still to come as a stream of tropical moisture feeds into a low-pressure system over the southern Murray Basin.
asserted
stream → follow → Basin
The system is notable for its slow movement, which should ensure moderate to heavy falls continue on Friday, with a focus across northern and eastern Victoria, along with the south-east corner of New South Wales.
asserted
falls → ensure → Wales
Isolated thunderstorms are also firing up near the leading edge of the rainband, and with abundant moisture and an overriding jet stream, storms could become severe and produce intense rainfall, with a lesser risk of damaging winds and large hail.
uncertain
storms → fire → winds
In the meantime, rain in South Australia has now mostly eased back to showers, although some coastal regions, including Adelaide, could still pick up another 10mm or more by Friday night.
uncertain
regions → ease → night
While the main band of precipitation has been shifting slowly east, as the low drifts towards Bass Strait on Saturday, it could re-circulate rain back across southern Victoria.
uncertain
it → shift → Victoria
It means moderate to possibly heavy falls and thunderstorms are still possible on Saturday across a large swathe of Victoria, along with central and eastern NSW.
uncertain
falls → mean → NSW
By Sunday the low should be slowly retreating in the Tasman Sea, although a few showers and storms are still possible in Gippsland and south-east NSW.
asserted
showers → retreat → Gippsland
Since this system is quite complex, let's go through the likely evolution of the weather during the coming days for our affected capitals:
asserted
's → let → capitals
Adelaide – showers are likely through Friday morning and afternoon, but modelling indicates they should mostly clear to the east in the evening with only the odd shower returning Saturday.
asserted
they → indicate → shower
The weather on Saturday depends on the exact location of the low, but the risk of heavy falls returning to Melbourne
asserted
risk → depend → Melbourne
All up, this event could bring more than 50mm to the outer metropolitan region, while the inner suburbs and CBD could pick up from 20 to 50mm, including what fell on Thursday.
uncertain
what → bring → Thursday
Rain is almost guaranteed both Friday and Saturday, including the risk of severe thunderstorms.
asserted
Rain → guarantee → thunderstorms
Modelling is indicating 20 to 60mm during the next 36 hours, before rain mostly clears on Saturday night.
asserted
rain → indicate → night
Sydney — rain should arrive later Friday from the west and could intensify on Saturday with possible thunderstorms.
uncertain
rain → arrive → thunderstorms
While moderate falls are possible, modelling is favouring the heaviest rain will remain just to the west and south of Sydney.
asserted
rain → favour → Sydney
Multiple catchments on Flood Watch
All up, the weather system is likely to drop at least 25mm south of a line from about Adelaide to Sydney, including pockets near 100mm over southern and north-east Victoria.
asserted
system → drop → Victoria
There are some indications parts of Gippsland could even see closer to 150mm, definitely enough to trigger river rises despite dry catchments after below-average rain through winter and September.
uncertain
parts → be → winter
As a result, a Flood Watch is in force for minor to moderate flooding across 16 separate catchment regions covering Gippsland, North East and Central Victoria.
asserted
Watch → cover → Gippsland
The moist tropical airstream is also producing a secondary area of rain across the western interior near another trough of low pressure.
asserted
airstream → produce → pressure
This outback rain could amount to 50mm, which is extremely unseasonable considering the WA interior averages only about 10 to 20mm through the entire month.
uncertain
interior → amount → month
Rapid turnaround after hot, dry September
Australia just experienced its second-warmest September on record, with the majority of the nation at least 2 degrees Celsius warmer than normal.
asserted
majority → experience → nation
But in such a large country there is always variability, and pockets of every state and territory did see September records fall, including Canberra, where temperatures landed at 2.35C above the city's long-term mean.
Sydney, Perth, Adelaide and Hobart all had their second-warmest Septembers on record, but the most extraordinary anomalies were over the outback, where temperatures were as much as 5C above the long-term mean.
Alpine Australia also experienced unprecedented early spring heat, including Thredbo, where temperatures were more than 1.5C warmer than the previous-warmest September.
For south-east Australia, it was also the second-driest September, but again, there are pockets that did see record low falls, including around central SA, the Victoria coast and along the central stretch of the NSW ranges.
asserted
that → be → ranges
But the wet start to October could be a sign of wetter months ahead, with modelling tipping further rain during the coming weeks, along with a general improvement in rain prospects as we transition into summer.
uncertain
we → tip → summer
The Aporia
