Extract from ABC News
Australia recorded its hottest spring on record and third hottest December on record. (Supplied: Christine Chandler)
A heatwave will spread from the north west to Tasmania this weekend and become severe in parts of eastern NSW and Gippsland.
And while the south-east sweats, the tropics are stuck in a holding pattern, with still no sign of the staple summer monsoon.
The ongoing absence of monsoon westerlies is unusual this deep into the wet season, and will result in its latest onset in at least 25 years — while also preventing tropical cyclones reaching our shores.
New Year's scorcher brings fire threat
In a repeat of the pattern seen numerous times through December, another heatwave is sweeping east across Australia.
This next burst of scorching temperatures developed in Western Australia this week, sending maximums as much as 17C above average on Thursday, including a high of 43C at Esperance on the state's south coast — the town's hottest January day in 12 years.
The broad mass of hot air then tracked through the western interior on Friday and is now descending over south-east states as a sweltering north-westerly blows south off the outback deserts.
Temperatures will exceed 40C on Sunday over much of south-east and central Australia thanks to a hot north-westerly airstream, bringing fire threats to some parts of the country. (Supplied: DFES incident photographer)
Today's highs should exceed 40C over northern Victoria, western NSW and inland SA, peaking at around 45C over the central interior.
And as temperatures rise so will the fire threat — despite relatively light winds, exceptionally low humidity down to just five per cent will lift dangers into the "extreme" category over Victoria's Wimmera and SA's Mount Lofty Ranges, Murraylands and south-east districts.
For coastal areas today, a brief afternoon sea-breeze will bring slight relief, although both Adelaide and Melbourne should still reach the mid to high 30s.
Parts of Perth baked through temperatures above 40C on New Years Day as the heatwave developed across WA. (Supplied: John James)
The hot north-westerly winds will continue through Sunday, leading to a second consecutive day above 40C for the south-east inland, however the heat will also reach eastern NSW, sending Western Sydney to 39C.
While humidity will rise tomorrow, freshening winds will offset the increase in moisture, again leading to extreme fire danger in parts of SA and inland Victoria.
Cool change to bring widespread rain
As with most heatwaves, relief will arrive in the form of a cooler southerly airstream off the Southern Ocean.
The wind change will reach the SA coast on Sunday afternoon, sweep through Victoria on Monday, then reach most of NSW on Tuesday.
Most regions can expect a 24-hour temperature drop of around 10 to 15C, for example Melbourne is forecast to fall from 38C on Sunday to 23C on Monday.
A cool southerly change will sweep east from the SA coast on Sunday afternoon, to reach eastern NSW on Tuesday.
So when will it reach each capital?
- Adelaide: late Sunday afternoon. Drop from the mid-30s to the mid 20s in a few hours.
- Melbourne: Monday morning. After a very muggy night above 25C a drop below 20C by midday.
- Canberra: late Monday night. After reaching the mid-30s a drop to the mind teens overnight.
- Sydney: early Tuesday morning. A 24-hour drop of up to 15C.
Modelling indicates the drop in temperature will also be followed soon after by a cloudband with widespread showers across the whole of south-east Australia.
For Sydney, if the fifth Australia-India Test goes to Day 5, the prospects of a showery, southerly change could prevent a result (good news for Australia who hold a 2-1 lead in the series).
The system is currently predicted to bring an average of 1 to 10 millimetres for most of SA, Victoria, and Tasmania, with totals closer to 10 to 20mm for eastern NSW.
Monsoon and cyclones remain MIA
This northern wet season is not following a traditional path as both the monsoon and tropical cyclones remain absent from the weather charts.
In the 25 years of the Bureau of Meteorology analysis charts, the average onset date of the monsoon trough on Australia's mainland is December 19, with the latest arrival on January 11, 2013 and the earliest on November 17, 2007.
The monsoon trough is the boundary between moist westerly winds which blow across the equator and easterly winds through the remaining tropics.
Along the trough is a near continuous and persistent band of thick cloud and rain, as opposed to the more sporadic showers and storms which develop over the tropics when the monsoon is absent.
The monsoon trough also spawns tropical lows and tropical cyclones, but so far this wet season the great rainmaker has mysteriously disappeared off our weather maps, only briefly appearing in the northern Indian Ocean in early December.
The lack of a monsoon explains why the Australian region has only seen one tropical cyclone this season, Robyn, and none anywhere remotely near the mainland.
So when will cyclones become a threat?
Modelling shows the true monsoon may not arrive on our shores until late January, easily the latest onset so far this century.
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