A pool of hot air is about to sweep across Australia, producing a spring heatwave in some areas and challenging records in others. The mass of hot air will intensify over northern and central Australia between Wednesday and Friday before drifting over the nation's eastern states on the weekend. Temperatures are forecast to climb 10 to 15 degrees above average in parts of South Australia, northern Victoria, NSW and Queensland between Friday and Sunday. This type of heat is unusual at this time of year and September temperature records may be broken in some places, most likely in NSW or southern Queensland on the weekend. Cooler weather will return to South Australia, northern Victoria and most of NSW by Monday, although a spring heatwave will grip parts of Queensland well into next week. For example, Longreach is forecast to climb 6-9 degrees above average from Thursday until at least next Tuesday. The hot weather will combine with dry and gusty winds to elevate fire danger ratings in a number of states later this week. The Queensland Rural Fire Service anticipate that fire danger ratings may reach severe in the state's south and southwest on Sunday.