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