Australian Monthly Climate Summary: September 2009
Thursday 1 October, 2009
September 2009 was another warm month over most of Australia, although not to the record-breaking extent of August. The month was wet over much of the southern fringe of the continent, but generally dry further north.
Over Australia mean maximum temperatures were 1.48°C above the long-term average (8th highest on record), the 14th time in the last 16 years that September maximum temperatures have been at least 0.8°C above average. They ranked fifth-highest (+2.34) in the Northern Territory and sixth-highest (+1.93) in Queensland, with New South Wales, Victoria and Tasmania also ranking in the top ten.
The only substantial region where maximum temperatures were below average was in Western Australia south of a Carnarvon-Eucla line. Over much of this area temperatures were 1−2°C below average and a few records were set in the far southwest. Elsewhere they were above average, by at least 1°C in most mainland areas away from the southern coastal fringe, and by 2−3°C over most of the Northern Territory away from the Top End, the southern half of Queensland, and New South Wales except for the northern and far southern inland. The peak anomalies, of 3−4°C, occurred in coastal NSW between Sydney and Coffs Harbour, the inland southeast of Queensland, and the southern Northern Territory. There were two main regions where records were set; along parts of the east coast, especially in northern NSW and in Queensland between Gladstone and Cairns, and in parts of the Top End and East Kimberley in north-western Australia. Rockhampton set a record high mean maximum temperature for the fourth month in succession.
Minimum temperatures were less extreme but still well above average (anomaly +0.95°C, 14th highest), with the Northern Territory again ranking fifth (+2.15). Nights were cool over much of southern Western Australia, being 1−2°C below average in many areas, and reaching record lows around Meekatharra. They were also slightly below normal along parts of the Murray River, and in northern inland NSW. Elsewhere they were generally above normal, especially in the Northern Territory, where anomalies widely exceeded 2°C in the south and west (and adjacent border areas of Queensland, South Australia and Western Australia), reaching 4°C around Alice Springs. Anomalies of 1−2°C covered the southern half of Queensland, the remainder of the NT, northern South Australia and the Kimberley region, and records were set around Alice Springs and in parts of the Kimberley.
*Fractional ranks denote tied values. **Anomaly is the departure from the long-term average.
National rainfall was fairly close to normal (13% below average, 51st highest of 110 years) and no state or territory ranked in the top or bottom 20 years. Rainfall was above average over most of the southern fringe of the continent, including most of Western Australia south of a Shark Bay-Kalgoorlie line, the agricultural areas of South Australia, and almost all of Victoria and Tasmania. Most areas further north had below-average rainfall, except locally in northern inland New South Wales, northern South Australia, and in a few seasonally dry parts of the northern tropics that received early-season thunderstorms.
There were few large rainfall anomalies on the mainland. While most of the southern fringe exceeded average rainfall, only in a few areas (mostly in central South Australia and the Victorian Mallee) did it reach 50% above normal or rank, even locally, in the highest decile. There were also few areas in the lowest decile. It was, however, a very wet month in eastern Tasmania, with records being set along the east coast between Swansea and Hobart. Along with a wet winter, this contributed to Tasmania experiencing its third-wettest June-September on record.
*Fractional ranks denote tied values.
**A new area-averaging method has been adopted for rainfall from May 2009. Current and historical totals for Tasmania are substantially higher than under the old scheme, but differences for other states, and nationally, are negligible.