Charts of the Past with Blair Trewin
Charts of the Past with Blair Trewin
BAMOS March 2017
27
14 August 1934
Late winter is a time when active weather systems regularly cross southern Australia, bringing strong winds and rain to the southeast, and dry windy conditions further north. Such systems were a more frequent occurrence in the first half of the 20th century than they are now, and August 1934 brought a particularly noteworthy example.
An intense low pressure system was positioned south of South Australia on the 13th. Whilst a lack of data from over the oceans makes it hard to determine with confidence the system’ s exact configuration, the low, combined with strong ridging over and south of southwestern Western Australia, brought southwesterly flow with a long fetch into South Australia. This flow remained in place through the night of the 13th and into the 14th; by evening, a closed low was centred southwest of Mount Gambier, before moving quickly eastwards to be east of Bass Strait by the morning of the 15th. It was a notably intense low; the pressure at Adelaide reached 986 hPa at 1.30 p. m. on the 14th, the lowest on record there at the time( subsequently surpassed in 1981 and 2016), whilst Sydney set an August record( at the time) of 992 hPa that evening.
The direction of the wind was ideal for a substantial storm surge to enter Spencers Gulf, and this transpired on the evening of the 13th, with major coastal flooding along its northern shores. Hardest-hit was Port Pirie, where much of the town was inundated( there are conflicting reports as to whether the collapse of an embankment contributed to this), with some parts of the town still under water three days later. Two deaths were reported( a rare instance of casualties in Australia from storm surge outside of tropical cyclones), and more than 300 families were left homeless. There was also significant flooding at Port Germein, where water depths of two feet were reported at the Post Office, and at Port Augusta.
High winds were also reported on land, with estimated gusts of 110 to 130 km h-1 over the Eyre Peninsula, causing widespread although mostly minor wind damage there, and in the Riverland and Mid-North. The strong winds also extended to the eastern outback with duststorms reported in western New South Wales and western Queensland.
Rainfall was widespread through southeastern Australia( including the southern outback, and the southern half of New South Wales). As is typical for systems of this type, general falls were modest( typically 5 to 20 mm over flat terrain over the three days 14 – 16 August), but were strongly amplified over and upstream of topography. The heaviest falls were in and near the Alps, and the Adelaide Hills and southern Flinders Ranges. In South Australia, 101.6 mm fell at Stirling over the two days 14 – 15 August, and 61.7 mm at Lobethal on the 15th, whilst further north 55.9 mm fell that day at Melrose. In the eastern states, noteworthy daily falls included 86.4 mm at Walwa and 72.1 mm at Hotel Kosciusko on the 15th, and 67.1 mm at Batlow on the 14th. Whilst temperatures were below normal, it was not a particularly cold system compared with some of its type; the coldest day was the 15th, with 13.2 ° C at Adelaide, 11.1 ° C at Melbourne and 8.6 ° C at Hobart.
This system also marked a transition from dry to wet conditions. The seven months from January to July 1934 had been very dry in many parts of the southeast, particularly in the agricultural areas of South Australia where seven-month rainfall totals were in the lowest decile. The August rains set the scene for four months of rainfall in the highest decile over most of the same regions. Whilst this was very beneficial for agriculture, it set the scene for disastrous floods in southern Victoria, including Melbourne, at the end of November.
Synoptic chart for 0900 AEST, 14 August 1934.