East coast lows

Rain in Sydney, 1986

East coast lows derive much of their energy from the warm waters of the Tasman or Coral Seas. The same waters provide a source of moisture for sometimes torrential rain, far in excess of that normally associated with cyclones outside the tropics. Such an event was responsible for Sydney's heaviest ever daily rainfall, in August 1986.

The winter of 1986 in Sydney had been the driest in almost a century, and with the bushfire season around the corner, rain was urgently wanted. Early on Monday 4 August, light rain began to fall, becoming heavier overnight, and heavier still next morning. It reached a crescendo between midday and 3pm on the Tuesday, when 100mm cascaded down. Rain continued through the evening, finally easing by about 2am on the Wednesday. The 24-hour rainfall total to 9 am Wednesday was a record 327.6mm, and even in the normally drier western suburbs, totals exceeded 250mm.

The torrential rains created chaos. Flooded roads prompted many motorists to abandon their cars, bus services were severely disrupted, and trains ground to a halt due to flooded tunnels. Many people, faced with difficulties and danger in getting home, stayed in the city that night. In the western suburbs, creeks rose rapidly and flooded houses. Tragic drownings occurred: in one case, two young children were torn from their father's arms by the water. And rain wasn't the only problem: on Sydney Harbour, strong winds and poor visibility seriously disrupted ferry services. Gales lashed the coast, and further south, huge seas created major problems for shipping off the Illawarra coast.

The rains eased in Sydney as the winds shifted more southerly early on Wednesday, but now the southern escarpment of the Blue Mountains became exposed to the downpour. The result was one of the largest floods on record on the Cox and Grose rivers. Heavy rains extended south to the Illawarra escarpment west of Wollongong, an area accustomed to drenchings from east coast lows. But on this occasion rain falling on the Georges River catchment added to already high water levels from rain in the Sydney area. The resultant flood covered the bridge at Milperra and cut the Hume Highway. Rains spilled west of the Divide, with the Macquarie breaking its banks at Bathurst.

The downpour occurred at what is normally a relatively dry time of year in Sydney. However, 12 years later another east coast low in August caused gales and heavy rains; though on that occasion rainfall in Sydney was slightly less intense and flooding less severe.

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