Australia is now in the peak of the severe weather season, and this weekend will offer up an assortment of atmospheric extremes from torrential rain and powerful afternoon thunderstorms to a sprawling heatwave.
The heaviest rain this weekend should fall across eastern Queensland and north-east New South Wales, where isolated totals could exceed 100 millimetres.
In the meantime, warm and humid tropical air will spread down the entire east coast and trigger thunderstorms from central Queensland to Tasmania.
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And the wet and stormy weekend could be a sign of what’s ahead for the rest of summer as the National Oceanic and Atmospheric Administration (NOAA) confirms La Niña conditions have emerged in the Pacific Ocean. And the Bureau Of Meteorology’s (BOM) seasonal outlooks continue to favour above median rainfall through the coming months.
And while the eastern seaboard ducks for cover, a heatwave will spread across half the country from the western interior to the tropical Queensland coast.
Deluge prompts Queensland flood watch
A classic black nor’-easter weather pattern is leading to substantial rain from central Queensland to the NSW Mid North Coast.
The term “black nor’-easter” has been used since the 18th century and describes the very dark clouds which form along Australia’s east coast when humid north-easterly winds feed copious moisture into a coastal trough.
A true black nor’-easter is supported by a low-pressure system above the surface which lifts and cools the moist tropical air to produce cloud and rain — the exact pattern unfolding this weekend.
The black nor’easter weather pattern dumped a large amount of rain on Friday. (Supplied: Melinda-Jane de Tugun)
The system already brought huge totals on Friday, including 161mm on Stradbroke Island in the 24 hours to 9am, and up 87mm in just 6 hours to 3pm just north of Miles.
The heaviest falls on Saturday will target the area from about Rockhampton to Port Macquarie, and inland to the Darling Downs, including Brisbane where the BOM predicts a 25 per cent chance of more than 40mm.
Modelling shows an average fall across the region from around 20 to 50mm, with a few pockets in excess of 100mm, promoting a flood watch for the Dawson and Burnett Rivers, along with a handful of rivers in southern inland Queensland.
The drenching should become more coastal on Sunday, with another 50mm possible along the NSW northern coastline.
Storms down entire eastern seaboard
The humid black nor-easterly will also provide the ideal conditions for summer storms, extending from tropical Queensland to Tasmania.
All eastern capitals are likely to see lightning at some point this weekend, and all could see storms both on Saturday and Sunday.
Thunderstorms are possible on Saturday right along Australia’s eastern coast and ranges. (ABC News)
Saturday’s thunderstorms could even turn severe along much of the Great Dividing Range, possibly extending to some coastal areas on Sunday.
The main threat this weekend is flash flooding thanks to slack winds and abundant moisture — environmental conditions which lead to prolonged heavy rain under storm tracks.
While a north-easterly and trough combo often leads to flash flooding in mid-summer, enhancing the risk this year is the very warm sea temperatures off our coasts.
Water temperatures in December were the highest on record around Australia, promoting increased evaporation and higher surface moisture — exactly what’s required to fuel towering storm clouds.
The seas are simmering up to 2.5C above average off the east coast and remarkably up to 6C above normal off the Pilbara coast. (ABC News)
Hail and damaging wind gusts are less likely from storms this weekend as both generally require drier and colder air in the mid-levels of a storm.
Heatwave spreads from interior to tropical Queensland
It’s been a summer of nearly continuous heatwaves across Australia, and while its obviously the hot time of year, this season has been extreme with a national mean maximum about 2 degrees Celsius above average.
Take Alice Springs for example — an average daily high this summer of 38.6C, well above the town’s long term mean of just below 36C.
And for other inland areas, even hotter temperatures are ahead during the coming days, including highs in the mid-40s for much of the central interior.
However, the heatwave is forecast to be most intense over tropical east Queensland — not because the region will see the highest temperatures, but rather the irregularity of prolonged heat near the coast.
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The stretch from Cooktown to Proserpine can expect a run of days about 35C and minimums as high as 27C, exceptionally uncomfortable temperatures considering the high humidity experienced near the coast.
BOM has therefore placed parts of tropical east Queensland in the “extreme” heatwave category, the highest rating which indicates dangerous health risks for even healthy people who don’t take precautions to keep cool.
La Niña officially declared
As reported by the ABC earlier this week, La Niña conditions have now emerged across the Pacific Ocean, confirmed on Friday by NOAA’s official declaration.
And while this year’s La Niña is likely to be a relatively short and weak event, the odds still favour rain across northern and eastern Australia during the next few months.
The latest BOM seasonal outlook shows the greatest chance of above median rainfall from February to April is over Cape York Peninsula, up to an 80 per cent risk of it being wetter than normal, while a broad band of 60 to 70 per cent probability extends through most of the tropics and down the east coast.
A wet January should be followed by above median rainfall from February to April across much of Australia. (ABC News)
However, BOM will not declare La Niña underway until its presence is confirmed for at least three months.
Considering the likely short duration of the current event, BOM’s strict guidelines could therefore prevent any declaration this year.
