July 2007

The July 2007 negative SAM event was the second-strongest negative monthly winter value on record. Higher than average pressures occurred around Antarctica and lower than average pressures in the southern parts of the Atlantic and Indian oceans, as well as large parts of the southern Pacific Ocean (see image). This meant the belt of westerly winds had shifted towards the equator, bringing more storm systems to southern Australia.

Mean sea level pressure anomalies for July 2007 for the southern hemisphere
Mean sea level pressure anomaly chart for July 2007 for the southern hemisphere. Base period is 1979–2000. Higher than average pressure is evident over Antarctica while lower than average pressure is located further north. Higher pressure near Antarctica and lower pressure in the mid-latitudes is a defining characteristic of negative SAM. Data: ERA interim.
Australian rainfall deciles for July 2007
Australian rainfall deciles for July 2007. Deciles relative to 1900–2018.

The July 2007 rainfall followed a typical negative SAM pattern for winter, with above average rainfall in southern Victoria and southwest Western Australia, and suppressed rainfall over New South Wales. However, Tasmania had a drier than average month; the opposite from what may have been expected with a negative SAM.