Extract from ABC News
NSW has been hit with violent thunderstorms. (ABC News: Andrea Jonson)
Australia's weather is again dominating news headlines this week, from ongoing flooding in Queensland, to a rapidly forming WA cyclone along with violent NSW thunderstorms.
While the north and east are being drenched, southern states are baking in yet another heatwave.
Temperatures on Wednesday soared as much as 18 degrees Celsius above average in SA — including a new state record for February of 48.7C at Oodnadatta.
Although February is still peak severe weather season, the majority of extreme events this month are being exacerbated by abnormally warm waters off our coastlines.
The sea surface temperature in January averaged 24.6C in Australian waters, the warmest on record for January and more than 1C above the long-term average.
The unprecedented warmth marks Australia's fourth consecutive month of record warm seas — a pattern that has continued into February.
Currently the greatest deviations from normal lie off the WA and NSW coasts where temperatures are as much as 3C above average.
Waters are so warm in the Tasman Sea they could theoretically support the formation of a tropical cyclone, sitting just above the threshold of 26.5C east of Sydney.
Australia is currently surrounded by warm waters, as much as 3C above normal off the WA and NSW coasts.
While multiple ingredients are typically required for severe weather, this abundant ocean heat is helping to fuel the events thanks to increased evaporation.
Essentially, the combination of warm waters and climate change results in more water entering the atmosphere, and more being held above the ground waiting to precipitate out as rainfall — since for every 1C increase in air temperature, the atmosphere can hold 7 per cent more water.
Snow to replace record February south-east heatwave
After Australia's second-hottest December-January on record, heatwaves continue to impact the country in February.
This week's edition is seeing temperatures climb well over 40C right down to the SA coastline thanks to a scorching northerly off the interior.
Adelaide weather stations recorded highs between 41 and 44C on Wednesday, including 43.3C at West Terrace, just 1C off a February record.
The hottest air will shift to eastern states on Thursday, but thankfully relief is ahead as a southerly change approaches from the Southern Ocean.
Temperatues and snow for the south-east.
Unlike most mid-summer changes, the cool winds have originated well south near Antarctica, and will therefore result in a significant temperature drop of up to 20C in 48 hours.
The cooler air is now pushing east through SA, and after a high just below 40C on Thursday, Melbourne can expect the change to arrive later tonight with a rapid drop to only 18C this weekend.
Despite being summer, the air will even be cold enough for highland snow across Tasmania this weekend, along with a possible brief dusting on the mainland alps on Saturday night.
Humid east faces further severe thunderstorms ahead of weekend snow
The weather pattern this week is ideal for thunderstorms across eastern Australia due to a warm and humid flow off the simmering Coral and Tasman seas.
NSW has already faced three days of severe storms this week, and further thunderstorms will develop during the coming days from Victoria to tropical Queensland.
A storm lights up the sky over southern NSW on Sunday night. (Supplied Dede Rang)
After a few severe storms on Thursday in Victoria and small pockets of Queensland and NSW, thunderstorms will become more widespread on Friday, extending from Victoria early across much of NSW and inland Queensland through the day.
Both Sydney and Canberra could see brief heavy rain and damaging winds in the afternoon, although storms should generally remain below the intensity seen earlier this week.
The humid and unstable air will then shift north, leading to thunderstorms across eastern Queensland this weekend.
Tropical Cyclone Zelia to become first to impact mainland
After a slow start to the wet season and the latest monsoon onset on record, tropical lows and cyclones are now becoming frequent on the daily weather maps.
The first five named systems of the 2024/25 Australian cyclone season stayed well away from the mainland, however, Tropical Cyclone Zelia is increasingly likely to become the first to reach land.
Zelia gathered strength through Wednesday, aided by ocean temperatures above 31C off the WA north coast, and the system is predicted to continue intensifying prior to crossing the coast from late Friday, although modelling is still extremely variable in the position and timing.
While it's too early to forecast the precise impact, Cyclone Zelia is currently an average-sized system by global standards, but with a relatively tight radius of cyclone-strength winds extending roughly 100 to 150 kilometres from the centre.
This relatively small field of gales should limit damage from wind and a storm surge to a localised region near the eye, with the magnitude largely dependent on the exact location of landfall.
A path directly over Port Hedland, or possibly even Karratha or Roebourne, at an intensity of category 3 or above is the worst-case scenario, while the impact would be significantly lessened if Zelia was to hit the sparsely populated coast to Port Hedland's east.
Rain forecast for WA cyclone.
One model's prediction of rain from Zelia shows from 100 to 400 millimetres across much of the Pilbara.
While cyclone force winds will be spatially limited, heavy rain will extend well away from the centre, extending around 300km to the east into the western Kimberley.
The key question after landfall then becomes whether the system stalls, as slow-moving ex-cyclones often cause far more damage from flooding than the original strike.
Thankfully, modelling is indicating Zelia should move steadily inland and dissipate by early next week, preventing a repeat of Cyclone Jasper in December 2023, which devastated north Queensland.
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