A pool of heat sitting over parts of eastern Australia today is causing elevated bushfire danger, thunderstorms and lots of sweat. Some areas over Australia's eastern inland have been locked in an early-summer heatwave since late last week. Daytime temperatures in northern New South Wales and southern Queensland have soared around 10 degrees above average since Friday. Birdsville in Queensland exceeded 46 degrees on Friday and Saturday, the first of which was the site's hottest December day in 26 years. Sunday was the hottest December day in 11 years at Bourke (45C) White Cliffs (45C) and Tibooburra (44C) in New South Wales. Nights have also been oppressive. Those living in Moree just slept through their warmest December night in 41 years after dipping to a low of 27 degrees. Last night was also the warmest for December in at least 20 years in St George, recording a low of 30. Closer to the coast, today's heat is combining with moisture and light winds to make it feel unusually muggy. High relative humidity is making it harder for sweat to evaporate from people's skin, preventing them from cooling down. Sydney's apparent temperature has been sitting around 28-31 degrees through most of the day, more than two degrees above the actual temperature at times. The city's residents endured conditions more typical of a tropical town than a mid-latitude harbour city. The heat is also helping cause severe fire danger ratings in some areas today, along with thunderstorms in parts of southern Queensland, New South Wales and northern Victoria. A cool change is on the way and will bring welcome relief from the early-summer heat by the middle of the week. A fresh southerly will bring a little respite to Sydney this evening, before a stronger change sweeps through New South Wales on Tuesday and southern Queensland by Wednesday.