First, Australia's temperatures...which averaged 104 degrees on Monday could be even hotter on either Saturday or Sunday. Computer modeling shows the potential for widespread areas of 100 degree heat across much of the nation's Outback, with 110 degree heat in some portions of interior New South Wales and South Australia. Earlier computer modeling suggested the possibility of temperatures over 122 degrees (50 Celsius), which prompted the addition of another color chart to their forecast temperature maps.
The GFS is "just" suggesting 115+ as the max on both Saturday and Sunday but it would not shock if some areas pushed 120 or higher. Australia's record is 123.3 degrees from January 1960.
The only relief will be along the south coast of the country, moderated by cooler ocean water from the Southern Ocean and resulting in temperatures that only get into the 70's and 80's. For instance, Melbourne on Australia's southeast corner, "only" got to 78 yesterday and had a steady south wind through the day. If they get a northwest wind, the downslope effect off of the hills to the city's north quickly can torch the city and such results have pushed the thermometer over 100 on a couple of occasions this month already.
Some of the temperature forecasts elsewhere aren't friendly. Sydney could crack 100 on Saturday, which would be their second 100+ day in a week's time after not hitting 100 since February 2011. Alice Springs, in the middle of Australia, could exceed 110 this weekend. It's hot and given their general dry conditions in the continent the fire threat will remain high for a number of days in many parts of Australia.
One exception to that could be along their western coastline. Cyclone Narelle has been steadily strengthening over the past couple of days as it tracks slowly south-southwestward. It's expected to come very close to the northwest tip of Australia this weekend before accelerating south and then southeastward early next week. It may come ashore right along the coast or pass just offshore, possibly providing a threat for heavy rain to areas along the coast or just inland. However, with fires ravaging across interior sections of Western Australia the relief from rains with this storm may not get far enough inland to help combat these fires.
More significant fires are raging across interior New South Wales and Tasmania in addition to those in Western Australia. The slow arrival of the summer wet season across Northern Australia is partly due to a stronger than usual ridge of high pressure over the country's interior, which is preventing the southward shift of the monsoon trough and is preventing thunderstorm development from taking place.