Australian Weather Calendar: September 2015

September photograph by Carlo Borlenghi ©Rolex

Roll cloud over first leg of Sydney to Hobart yacht race, New South Wales

In over 30 years following yacht races around the world, Carlo Borlenghi has only seen two roll clouds—one in Sardinia, west of Italy, in 2008; and this one, preceding a southerly buster on the first leg of the 2010 Sydney to Hobart race.

A southerly buster is an abrupt southerly change off the New South Wales coast, typically accompanied by fierce winds and a rapid drop in temperature. The approaching boundary between warm and cold air is distorted into an 'S' shape as the western side is trapped against the Great Dividing Range and slows compared to the eastern edge travelling over the ocean. Read more in our blog: The big bust—southerly busters explained.

Carlo's photograph was taken with a Canon D1X camera and a 16–35 mm lens.