The heat currently affecting southeastern Australia is rare, covering an unusually large area, not just for this time of year but even for summer. Today much of South Australia, Victoria, New South Wales and Queensland is heating up to the mid-to-high thirties and the ACT and many coastal areas reaching the low thirties. Adelaide, Melbourne, Canberra, Sydney and Brisbane are all forecast to reach 30 degrees or hotter. If each of these capitals do reach 30 degrees today it will be only the 28th time in the past 75 years it has been achieved. It will also be the earliest in the season in the past 75 years, breaking the previous record by 26 days. The main contributing factors to this unusual hot spell are - - a lack of moisture in the air to allow sunnier-than-normal days, hence hotter-than-normal days over central and northwestern Australia - weaker than normal cold fronts allowing heat to build over the southern inland - weak high pressure systems and low pressure troughs keeping winds light and coastal sea breezes week The unusually large area of heat is also unusually long for this early in spring, leading to a record-breaking run of three-or-four days of 30-degree heat for many locations. The size of the hot area will shrink in the next few days once the strongest cold front in a few weeks moves through. The front will bring a colder change to Adelaide and Melbourne on Tuesday, Canberra and Sydney on Wednesday and Brisbane on Thursday, taking the hot air back to the interior.