The spring temperature seesaw will swing in Sydney today as a southerly buster bears down on the sweaty city. Clear skies and warm northerly winds ahead of an approaching cold front sent the mercury soaring across Sydney this morning. After the city's warmest morning in more than a month (20.3C), the temperature had already reached 30.6 degrees before 10am and is forecast to reach a top of 35 degrees later today. This would be Sydney's hottest day since February and 13 degrees above average for this time of year. Temperatures could be even higher in western Sydney, where Penrith and Richmond are forecast to reach tops of 36 degrees this afternoon. Sydney's hottest days at this time of year occur ahead of approaching cold fronts and this typical springtime pattern causes abrupt temperature fluctuations when the change arrives. Today's Southerly Buster is expected to sweep through the city between 4pm and 6pm, bringing blustery winds and an abrupt drop in temperature. Some suburbs are likely to cool by more than ten degrees in under an hour when the southerly buster arrives. Brief and fast moving showers and thunderstorms are also possible ahead of the change. The temperature will be noticeably cooler across Sydney tomorrow, reaching 21 degrees in the city and 24 degrees in the west.