Charts of the Past with Blair Trewin
BAMOS June 2017
30
Charts of the Past with Blair Trewin
1 February 1993
A typical scenario for prolonged heatwaves in southeastern Australia is a blocking high in the Tasman Sea. After a very cool and wet spring and early summer, conditions warmed in January with monthly mean temperatures near average over most of the region, but without any significant extreme heat.
This changed in late January. A high-pressure system formed over Tasmania on 30 January, then moved into the Tasman on the 31st, with little change until a trough crossed the southern coast on 4 February. The system was extensive and directed northerly to north-easterly flow over areas as far west as the Nullarbor and as far north as southern Queensland.
Compared with some more recent heatwaves, the highest temperatures in the early days of February were not extreme, generally reaching the high 30s and low 40s in Victoria, South Australia and inland New South Wales. On 1 February, the highest temperature in these states was 43.1 ° C at Tarcoola, whilst Victoria peaked at 41.2 ° C at Warracknabeal and New South Wales at 40.2 ° C at White Cliffs, which would later reach 45.3 ° C on the 4th. At Adelaide, each of the four days from the 31st to the 3rd had maxima between 39.1 ° C and 41.5 ° C, whilst Melbourne peaked at 41.3 ° C on the 3rd ending four consecutive days above 35 ° C.
Whilst the heatwave lacked intensity, it was exceptionally extensive. It is one of only three instances where heatwave conditions have occurred simultaneously in Brisbane, Sydney, Canberra, Melbourne, Adelaide and Hobart, although the heatwave only reached severe intensity in a few places, and did not reach extreme intensity anywhere. In South Australia, every station in the state reached 30 ° C on each of the three days from 1 to 3 February, a sequence which has only been matched once, in January 2014.
The heatwave was accompanied by thunderstorm activity, especially in Victoria. The 1st was the most active day, with severe thunderstorms reported in many parts of central and western Victoria. Whilst the heaviest rainfalls were in the Yarra Ranges( 63 millimetres near Warburton), severe winds were more prominent further west. Possible tornadoes were reported at Ararat and Elmore, and 2 cm hail at Trentham. The thunderstorms, following a 37.8 ° C day, impacted what became an( in) famous Guns N’ Roses concert at Calder Park raceway northwest of Melbourne. Thunderstorms also occurred on the 2nd and 3rd, but were more localised. Apart from gusts with local thunderstorms, winds were generally light through the event and no significant bushfires occurred in any southeastern states in the early days of the month.
In northwestern Australia, heavy rain occurred as a result of a tropical low, which formed over the Top End on the 27th and drifted slowly southwest, affecting the Kimberley at the start of February and the Pilbara over the following days, by which time it had also absorbed the remnants of Tropical Cyclone Lena which had been off the northwest coast during the period. From 1 to 4 February, most of the Kimberley received at least 100 millimetres( with 178 millimetres falling on the 1st at Carranya in the east Kimberley), and most of the Northern Territory north of Tennant Creek had at least 50. This rain caused widespread flooding, especially in the Halls Creek and Fitzroy Crossing areas, as a prelude to even more severe flooding in the last week of the month.
After 4 February, the heat retreated to inland areas, with the event’ s highest temperature( 46.9 ° C) occurring at Tarcoola on the 6th. A more substantial change brought sustained cooling( along with some fires in Tasmania) on the 7th.
Synoptic chart for 0000 AEST, 1 February 1993