Parts of Victoria and SA will experience their highest temperatures in eight to nine months today as the mercury soars 15 degrees above average in both states. A tongue of hot air is being carried into the nation's southeast today ahead of an approaching trough. At 11:20am AEDT, Hobart (25C) and Melbourne (28.9C) were warmer than Sydney (21.4C) and Brisbane (24.6C), while Adelaide (33.8C) was the hottest state capital city in Australia. Melbourne's forecast top of 34 degrees this afternoon would make this the city's warmest day since February and 12 degrees above average for this time of year. It is also day two of three in a low intensity heatwave for central Victoria. Temperatures are expected to climb 15 to 16 degrees above average for this time of year in Hamilton (37C), Warrnambool (36C), Mount Gambier (36C) and Mortlake (36C) this afternoon. Despite the unseasonable heat, these forecasts fall short of the record November maximums of 45.8 degrees in Victoria and 47.9 degrees in SA. Hobart's forecast top of 31 degrees would be 12 above average for November, although the city had a slightly warmer day last month. A cool change will sweep across southern districts of SA today and progress over Victoria and Tasmania tomorrow, triggering showers and storms with its passage. Temperatures are likely to drop by 10 to 15 degrees in the wake of the change, with some areas possibly cooling by up 17 or 18 degrees within 24 hours.