Australian Monthly Climate Summary: August 2008
Monday 1 September, 2008
August was a cool and dry month through most of Australia, although a major rain event, accompanied by above-normal temperatures, in the last few days of the month lifted temperatures and rainfall from potentially record-breaking levels over substantial parts of the continent.
Both daytime and overnight temperatures were below normal over most of the continent. Averaged over Australia, daytime maximum temperatures were 0.80°C below the long-term average (10th lowest in the 1950−2008 period), and overnight minimum temperatures were 1.08°C below (9th lowest), the coldest since 1989 and 1994 respectively. Area-averaged maxima and minima were below average in all states and territories, except in Tasmania where maxima were slightly above average.
Maximum temperatures were above normal along much of the northern and western coast, with anomalies reaching 1−2°C between Exmouth and Perth and locally around Broome and Darwin, but below normal almost everywhere else except eastern Tasmania. They were at least 1°C below normal over a vast area, encompassing most of South Australia, western Victoria and New South Wales, the Northern Territory south of Katherine, and adjacent parts of western Queensland and eastern WA. The largest departures from normal were in central Australia, where temperatures 2−3°C below normal were in the lowest decile. Maxima were also 1°C or more below normal in areas around Sydney and along the Tropic of Capricorn in eastern Queensland. Both areas were in the lowest decile, as were western Victoria and South Australia from Adelaide southwards, whilst the only areas which reached the highest decile were small regions around Shark Bay and east of Darwin.
The month was marked more by consistently cold conditions than by individual extreme events, particularly in the south-east, where Mount Hotham set a new Australian record by failing to rise above 0°C for 53 consecutive days from 7 July to 28 August. Despite the consistent cold, below-normal precipitation has resulted in a near-normal snow cover at high elevations.
Below-normal overnight minimum temperatures were even more widespread, with positive anomalies confined to the northern Pilbara and western Kimberley regions in Western Australia, and a small area near Kalgoorlie. The cold nights were particularly pronounced in northern New South Wales and south-eastern Queensland, where minima were 2−3°C below average and records were set in places, especially the Hunter Valley, the NSW North Coast and in the Moree/Walgett area. New South Wales had its second-lowest mean August minima on record (1.47°C below average). Minima were 1°C or more below average over large areas. One such area covered the northern and western Northern Territory, eastern Western Australia and South Australia (except the north-east corner), and another northern Victoria, most of New South Wales except the far south-east, and Queensland south of a line from Townsville to the south-west corner. Minima were also 1−2°C below normal in much of the south-west of Western Australia.
A new all-time state record for Western Australia was set on 17 August when Eyre, on the Nullarbor coast, reached −7.2°C, breaking the previous record of −6.7°C, set at Booylgoo Spring (near Sandstone) in July 1969. Eyre has a record of being prone to very cold overnight minima in clear, calm conditions, due to the site’s location in a hollow with nearby bare sand, and has previously set WA state records for the months of September, October and November. Another notable observation was −12.8°C at Glen Innes Airport on 9 August, equalling that site’s record from July 2002.
* Anomaly is the difference from the long-term average
Over the nation as a whole rainfall was 43% below the long-term (1961−90) average, making it the 14th driest August in the 1900−2008 period. Almost all of the southern half of Australia saw below-normal rainfall, except for parts of South Australia around Adelaide and the north of Spencers Gulf, and the far south coast of New South Wales, extending into far eastern Victoria. It was the driest August on record (77% below average) for the south-western region of Western Australia, with the majority of locations south-west of a Perth-Bremer Bay line setting records, along with some on the coast north of Perth. Almost all of the area south-west of a Shark Bay-Esperance line was in the lowest decile. Rainfall was also in the lowest decile in parts of inland eastern Tasmania; elsewhere in the south-eastern states, August rainfall was mostly 20−60% below average, but not in the lowest decile.
The rain event at the end of the month brought above-average monthly rainfall to a band extending from the east Kimberley region (WA) through the southern Northern Territory into northern South Australia and the far south-west of Queensland (with some patches in the highest decile), but these areas are normally dry in August and the actual rainfall amounts involved were small (less than 10 millimetres in Western Australia, and 10−30 millimetres elsewhere). The remainder of Queensland was dry with monthly rainfall in the lowest decile along most of the coast.