Australian Monthly Climate Summary: April 2008
Friday 2 May, 2008
April was a dry month in most of Australia, particularly in the tropics as the wet season came to an early end. It was also notably cool overnight over the east and north of the continent. Daytime maximum temperatures were generally fairly close to normal.
In most areas daytime maximum temperatures were close to normal. The national average was 0.21°C above the long-term (1961-90) mean (25th highest of 59 years), and no state or territory was in the top or bottom 10. The most extensive areas of above-normal maximum temperatures were in the interior of Western Australia, western South Australia and the southern two-thirds of the Northern Territory, but anomalies only reached +1°C locally in the western NT and eastern WA. The most significant cool area was the coast and adjacent ranges of New South Wales, where maxima were generally 1-2°C below normal, and some records were set around Sydney and Coffs Harbour. There was a major cold outbreak at the end of the month which saw snow falling to quite low elevations (for April) in southern and central New South Wales, and an Australian record low April maximum temperature of −3.2°C at Mount Hotham (Victoria) on 28 April.
Overnight minimum temperatures averaged over Australia were the third-lowest on record for April (1.09°C below normal). Eastern and northern Australia were especially cool. Most of Queensland was at least 2°C below normal, reaching 5°C in some inland locations (such as Tambo and Richmond), and the statewide average of −2.72°C was the lowest since 1951. The exceptionally cool conditions also covered much of the northern tropics, particularly locations where the wet season finished early, with anomalies of −3 to −5°C extending across the Northern Territory from the Gulf into the WA Kimberley. New South Wales (−2.06) also ranked fifth-lowest. Records were set in much of northern inland Queensland and the northern Northern Territory, as well as around Walgett in northern inland New South Wales. Warm minima, reaching up to 2°C above normal in the Pilbara, were largely confined to central and eastern Western Australia, although parts of the southeast were close to normal.
* Anomaly is the difference from the long-term average
Over Australia it was the 14th driest April from 109 years of record (58% below normal). All states and territories had below-normal rainfall for the second successive month. Tasmania was the wettest state by some margin but was still 34% below normal, whilst Queensland (85% below normal) had their third-driest April on record, and their driest since 1951.
The only substantial areas with above-average rainfall for April were the western areas of Western Australia, west of an Esperance-Kalgoorlie-Karratha line, and the New South Wales coast between Sydney and the Queensland border. Both regions saw persistent rain with some areas in the highest decile, and April records set in Perth, Taree (NSW) and around Shark Bay.
In contrast, there was little or no rain through a vast area of the interior, including most of the Northern Territory south of Katherine, most of inland Queensland west of Roma (and some coastal areas between Townsville and Rockhampton), northern South Australia, eastern Western Australia and an area of New South Wales extending north-west from Dubbo. In most of this area rainless Aprils are not unknown. Rainfalls in the lowest decile covered most of Queensland, extending into northern inland New South Wales, except Cape York Peninsula and parts of the southeast. There was also areas in the lowest decile around Melbourne and Hobart.
Northern Wet Season (October-April):
April also marked the end of the tropical wet season (October-April). Rainfall averaged over northern Australia (north of 26°S) for the season was almost exactly normal (0.2% below). The northern tropics and eastern and central Queensland were generally wetter than normal, with some areas (particularly in central Queensland) in the highest decile; in contrast, the southern two-thirds of the Northern Territory, and adjacent areas of far western Queensland, were very dry with seasonal rainfall 60-85% below normal. Tennant Creek and Mount Isa both had their driest wet season on record. Overall Australian-region (0-40°S, 90-160°E) tropical cyclone activity was near normal, with 10 cyclones reported, but cyclone impacts were modest, with only one cyclone (Pancho) briefly reaching category 4 intensity, and only two (Helen and Nicholas) making landfall, both at category 2 or below. Helen, and its remnants, was responsible for widespread flooding as it moved across the NT Top End and into Queensland.