Australian Monthly Climate Summary: April 2007
Monday 7th May, 2007
April was a generally warm and dry month over most of Australia, although a major rain event over southern parts of the continent in the month’s final week was sufficient to lift rainfall totals above monthly averages in some areas, particularly in South Australia.
April was also a warm month, particularly for daytime maxima. The national anomaly +1.26°C (5th highest on record), and Queensland (4th highest), Victoria (4th) and South Australia (5th) also ranked in the top five. Maximum temperatures were above normal over most of the continent, although they generally fell well short of the exceptional values observed in April 2005. The only areas which were cooler than normal were some patches in northern Australia north of 18°S, parts of the New South Wales coast, and the area around Carnarvon (Western Australia).
In contrast, maxima were 1°C or more above normal over a large area, covering almost all of South Australia, Victoria, New South Wales, the southern Northern Territory, and southern and central Queensland, except for a strip along the eastern coastal fringe. Over most of this area maxima were in the highest decile, with record values locally north of Brisbane and on Kangaroo Island. They also exceeded this level in parts of southern Western Australia away from the coast, and in northern Tasmania. Anomalies were in the +2 to +3°C range in inland southern Queensland, south-eastern South Australia and western and central Victoria, and scattered patches elsewhere.
Overnight minima were cooler than daytime maxima, but still generally above normal (national anomaly +0.46°C, 22nd highest on record). The warmest minima were in South Australia (5th highest on record), with most of the state 1°C or more above normal, and record mean values in the southern Eyre Peninsula. Similar warm anomalies, locally reaching +2°C, also occurred in adjoining parts of the southern Northern Territory, far southwestern Queensland and southeastern Western Australia, as well as in the southern and central ranges of New South Wales. In contrast, minima were below normal in much of northern and southeastern Queensland, particularly on Cape York Peninsula where they were in the lowest decile (anomalies near −1°C), and northern parts of the Northern Territory. Cool anomalies (around −1°C) also occurred on the western coast of Western Australia from Carnarvon southwards.
* Anomaly is the difference from the long-term average
April was extremely dry over most areas until its final week, with an early end to the tropical wet season in most of northern Australia, and persistent high pressure over the southeast of the continent. The late-month rain event first brought widespread rain to parts of central Western Australia on the 24th and 25th (a fall of 22 mm in 24 hours at Carnarvon was more than they had received in the previous 11 months), then the plume of tropical moisture interacted with a developing low-pressure system over the Great Australian Bight to generate significant rain over most of New South Wales, Victoria and South Australia, most of which had had little or no rain for April prior to the event. South Australia was particularly favoured, with four-day totals from 26−29 April exceeding 50 mm over a broad area centred on Adelaide, and reaching 150−180 mm in the Adelaide Hills. In magnitude and extent it was probably the most significant April rain event in the region since 1998.
As a result of the late rain event, April rainfall was above normal over most of South Australia (except the far south-east), north-western Victoria, and a belt of central Western Australia extending from Carnarvon to Newman, with parts of all these areas (particularly around Adelaide) being in the wettest 10% of all years. Separately, rainfall was also slightly above average in most of south-western Western Australia (more so around Esperance, where some records were set), the eastern coast around Sydney and Newcastle, and a few locations in the far north of Cape York Peninsula and the Torres Strait Islands. Elsewhere, it was a dry month. Areas in the lowest decile were scattered throughout the northern half of the continent, as well as covering most of Tasmania (except the east coast) and areas east of Melbourne.
Australian average rainfall was 39% below normal for the month (36th lowest of 108 years). Tasmania (−64%) had its fifth-driest April on record, and Queensland and the Northern Territory were 73% and 75% below normal respectively. There were positive anomalies in South Australia (+14%) and Western Australia (+12%).
There were no tropical cyclones in the Australian region during the month.