Australian Seasonal Climate Summary: Summer 2007/08 (December-February)
Tuesday 4th March, 2006
It was a rather wet summer through large parts of Australia, particularly in the east which was particularly favoured by systems associated with the mature La Niña event in the Pacific. The northern tropics also had a wet summer, as did most of the southern half of WA, but the centre of the continent was dry. National summer temperatures were fairly close to normal, with daytime maxima slightly below normal and overnight minima somewhat above normal as increased cloud cover suppressed the diurnal temperature range.
Daytime maximum temperatures were slightly below normal (0.14°C below the 1961−90 average, 21st lowest on record), with the most substantial cool areas in those parts of the eastern states affected by above-average rainfall and cloud cover. It was especially cool in southern inland Queensland and northern inland NSW, with maxima 2°C or more below the 1961−90 average over much of the area, reaching 3−4°C below normal between Charleville and Bourke. Most of this area had maximum temperatures in the lowest decile but few records were set. Weaker cool anomalies extended to the east coast, and it was also cool in many parts of the northern tropics, especially the Kimberley.
In contrast, maximum temperatures were well above normal in the southern half of the Northern Territory where little rain fell, reaching 2−3°C above normal around Tennant Creek. They were also slightly above normal in Tasmania, most of Victoria and SA, and parts of southwestern and interior WA, although anomalies only reached +1°C in a few areas. State anomalies in the NT (+0.97°C, 8th) and Tasmania (+1.05°C, 9th) were in the top ten.
Overnight minimum temperatures were generally above normal, with the Australian average 0.45°C above normal (13th highest). The most significant area which was cooler than normal, coinciding with the most anomalous rains, was inland Queensland south of Richmond, along with northern inland NSW, although even there anomalies were much weaker than for maxima, only locally reaching −1°C with nowhere in the lowest decile. Most other areas had above-normal minima except for a few patches scattered through WA and coastal SA.
The warm overnight conditions were particularly pronounced in the southern half of the Northern Territory, where anomalies reached record levels of near +2°C around Tennant Creek and were +1 to +2°C across most of the region. Anomalies in this range also occurred in the Riverina region of New South Wales, central and north-central Victoria, north-eastern Tasmania, and patches in southern Western Australia and southern Queensland. The NT (+0.95°C) had its second-highest mean summer minima on record, while Tasmania ranked tenth.
* Anomaly is the difference from the long-term average
Australian average rainfall was 19% above the 1961−90 normal (18th wettest on record). The most notable area of above-average rainfall was in the eastern part of the continent, particularly in Queensland and NSW. It was wetter than normal over most areas east of a line Burketown-Longreach-Swan Hill-Portland. It was especially wet in central Queensland and northern inland NSW, with seasonal rainfall in the highest decile in a band extending from the Atherton Tableland through Emerald and the Maranoa-Warrego areas of southern Queensland into north-central NSW. Rainfall in the highest decile also occurred along the Queensland coast between Townsville and Rockhampton (where February was especially wet), in north-eastern NSW and around Sydney. A few records were set around Coonamble (NSW) and inland from Mackay (Queensland). Queensland’s statewide average was the tenth-highest on record (34% above normal), whilst New South Wales was 40% above normal and the Murray-Darling Basin 47% above normal. (However, rainfall in the alpine region which is critical for Murray-Darling inflows was only slightly above normal, as it was in most of Victoria).
It was also wet in most of the Top End of the NT and the Kimberley region in the north of WA. Falls in the highest decile were common through this region, and records were set locally in southern Arnhem Land. The other major wet area was the southern half of WA apart from the far south-west. Much of the rainfall in this region was the result of a single event, the passage of the remnants of Tropical Cyclone Nicholas in late February, although there were also significant rains in December in places. The most favoured areas from the two events reached the highest decile.
In contrast, it was rather dry in most of central Australia, particularly the southern half of the NT, where there were widespread areas in the lowest decile, as there were in adjacent parts of interior WA and far western Queensland. A small area near the NT/Queensland border east of Tennant Creek had its driest summer on record. Most of South Australia was seasonally dry, whilst a wet February lifted Tasmanian rainfall to near normal after a very dry January.
Tropical cyclone activity for the season to date has been fairly close to normal with six named cyclones in the Australian region (90−160°E) as of 29 February, although there has not yet been a severe (category 3 or greater) landfall on the Australian continent this season.