Heat is building over inland parts of Western Australia and those living in the nation's south should take note. A weakening of the monsoon trough in the wake of Tropical Cyclone Rusty has allowed heat to gradually build across inland parts of Western Australia. Over the last two days, temperatures have soared to the mid-forties in parts of the Gascoyne and Pilbara, reaching 45 degrees at Nyang for the first time in March since 2008. The mercury hit 44 degrees in Denham and 43 at Shark Bay Airport on Friday, making it the hottest March day in six years for both locations. While these uncomfortable temperatures are occurring more than 2000 km from capital cities in South Australia and Victoria, the heat isn't as far away as some may think. The vast western interior of Australia acts as a major heat farm for the nation's southern and eastern states. Air masses that become intensely heated here can be swept over South Australia, Victoria, Tasmania and even New South Wales in a matter of days by strong frontal systems. One such system is brewing off the western coast of Australia and will cause temperatures to rise over coming days for already sweaty Adelaide and Melbourne. Both capital cities are currently experiencing extended hot spells, with Melbourne likely to see its longest run of march days over 30 degrees on record. Adelaide is expected to have 12 days in a row over 30, which has only happened three times before in recorded history. The real challenge will come from Monday in Adelaide and Tuesday in Melbourne as Western Australia's hot air mass gets pushed east across both cities. Temperatures are likely to push into the high-thirties in Adelaide on Monday and could get close to 40 degrees on Tuesday. Melbourne will see temperature push into the high-thirties from Tuesday, with Wednesday a chance to be the hottest day since mid-January. The front responsible for the escalating temperatures will bring a much cooler and probably welcome air mass to Adelaide and Melbourne by the end of the week. Thursday and Friday should be around 10 degrees cooler, dropping below 30 degrees for the first time in more than week.