Eastern Australia’s first big heatwave of spring will send temperatures soaring 12C or more above average in regions including Sydney by early next week as a weather pattern more typical of mid-summer takes hold.
“A deep, deep column of warm air” has built up over Australia, Karl Braganza, national manager of climate services at the Bureau of Meteorology, said. “You typically see that occurring in January.”
Melbourne’s maximum temperatures will approach 10C above the average for September for the coming week. Current forecasts have most of Sydney collecting multiple days of 30C or hotter over the next week – including at least six in a row for the city’s west starting Friday – reaching as much as 12C above normal.
Melbourne and Sydney are predicted to break records for the number of warm days in a row in September, said Ben Domensino, a senior Weatherzone meteorologist.
The Victorian capital is forecast to clock eight days of 20C or warmer, beating the previous record of seven such days set in 1907 and 1987. Sydney’s five days of 28C or hotter weather would break the current record of four such days set in 1928, Domensino said. Canberra is expected to match its record of six days of 23C or warmer.
Fire danger warnings for Sydney and surrounds will also reach “high” levels on Saturday. “It’s a bit of a heads-up of what we can expect in coming months,” he said.
Early spring in southern Australia is usually marked by turbulent conditions as warm and cool airflows contend, generating cold fronts and cut-off lows. This year, however, has seen fronts – including one that hit Perth in the west on Wednesday – quickly peter out, blocked by high pressure systems sitting over inland Australia.
“Seeing that kind of weather in early spring is generally indicative [that] you’re likely to be in for a warmer late spring and early summer period,” Braganza told Guardian Australia. It’s also typical of years when climate drivers – such as an El Niño – favour drier and hotter conditions over southern Australia.
The Bureau of Meteorology said this week in its fortnightly update that an El Niño was “very likely” to develop in coming months, as was the positive phase of the Indian Ocean Dipole.
The bureau has changed the frequency of its updates to weekly. Braganza said meteorologists would continue to watch developments in both the Pacific and Indian oceans before making the calls.
The US National Oceanic and Atmospheric Administration (Noaa) and the World Meteorological Organisation – both of which use different gauges from the BoM’s – have already declared an El Niño to be under way.
“All of the indicators are pretty much there. We’ve just got one – with the trade winds – that doesn’t meet El Niño thresholds,” Braganza said. Provided the Southern Oscillation Index maintains its 90-day average of minus 7, an El Niño declaration was likely in the next week or two, he said.
The bureau said Melbourne may also break its record for the number of days in a row in September of 23C or warmer. It has eight forecast, and the previous record tally was six.
Richmond, on Sydney’s north-west edge, is also forecast to have six consecutive September days above 30C. The current record stands at four.
Inland areas of NSW areas east of the ranges and the Hunter Valley were other regions of unusual prolonged warmth, as were part of South Australia on Sunday and Monday, and the north-east and eastern parts of Victoria on Monday and Tuesday, the bureau said.
Some records are already tumbling. Falls Creek, a snow resort in Victoria, reached 16.2C on Thursday, beating the previous September record by more than 2C.
Domensino said a positive phase of the Indian Ocean Dipole (IOD) and an El Nino would tend to produce more extreme hot days rather than prolonged spells of heat for southern Australia.
With the background influence of global heating, “temperatures approaching 50C are becoming more likely in some Australian cities”, he said. Penrith, in Sydney’s west, reached 48.9C on 4 January 2020.
Braganza said the bureau was “line ball” as to calling an El Nino this week. On current forecasts, an El Nino event looks likely to last until next autumn, models show.
The 2019-20 Black Summer bushfires had a positive IOD but not an El Nino. “Having them together in the current climate could be reasonably significant, he said.
Both events tend to reduce convection and therefore rainfall off Australia’s north west for a positive-IOD and off the north-east during an El Nino. On present forecasts, a positive IOD could start soon and last until the summer.
“The more the [climate] drivers are in phase, the less likely you will have just random weather breaking up the pattern,” Braganza said. “It’s a reinforcing of the atmosphere-oceans set up that leads to dry conditions, particularly in eastern Australia and the southeast.”
