Fire danger ratings are escalating across Victoria and South Australia, particularly in the Wimmera region, where bushfires have already consumed over 76,000 hectares since mid-December.

A notable cool change is expected to arrive on January 6, bringing showers and thunderstorms, which will lead to significantly cooler temperatures in the following week.

Sydney's temperatures are projected to reach a maximum of 29°C on January 4, rising to 34°C on January 5, and 35°C on January 6, with Penrith forecast to reach 39°C on January 5 and 40°C on January 6.

A heatwave is currently impacting much of south-east Australia, with temperatures expected to soar above 40°C in certain areas over the weekend, creating severe fire risks.

Meanwhile, in New South Wales, Hay is expected to reach 42°C on January 4, with Deniliquin and Corowa predicted to hit 41°C, and Griffith set for 40°C.

Jonathan How from the Bureau of Meteorology has urged residents in South Australia, Victoria, Tasmania, New South Wales, and the ACT to remain cool and vigilant about extreme fire dangers, especially in the Grampians national park, which is currently facing a bushfire.

In Melbourne, temperatures are forecasted to peak at 38°C on January 4 and 37°C on January 5, before a significant drop to 22°C on January 6, accompanied by widespread showers.