Extreme heatwave conditions will affect parts of southern Australia during the second half of this week. A large pool of hot air building up over central Australia will slowly sweep across the nation's south between Thursday and Sunday. Temperatures are likely to climb up to 10 to 15 degrees above average in parts of South Australia, Victoria and Tasmania during the four-day heatwave. The hottest weather for many locations will occur on the weekend as a tongue of northerly winds drags torrid air from the interior towards the south coast. Some places in South Australia are forecast to get within one or two degrees of their maximum temperature records on Saturday or Sunday. The prolonged nature of this event will cause severe heatwave conditions across most of South Australia and Victoria. Much of Tasmania will experience an extreme heatwave, which is the highest possible category. Hobart is forecast to have its hottest pair of days in four years this weekend, reaching the low to mid thirties on Saturday and Sunday. This mix of hot, dry and windy weather will also elevate the fire danger ratings in the coming days.