<P> The city is rarely affected by cyclones, although remnants of ex-cyclones do affect the city . The city is prone to severe hail storms, such as the 1947 Sydney hailstorm, wind storms, and flash flooding from rain caused either by East Coast Lows (during autumn - winter periods) and ex-tropical cyclone remnants (during summer periods). East Coast Lows are low pressure depressions that can bring significant damage by heavy rain, cyclonic winds and huge swells . Scientists have predicted that rainfall will become more unpredictable and temperatures will be on the rise . </P> <P> A notable event was the great Sydney flood which occurred on 6 August 1986 (unusual in that month) and dumped a record 327.6 mm (12.90 in) on the city in 24 hours . This caused major traffic problems and damage in many parts of the metropolitan area . The next notable event was the 1999 hailstorm, which caused severe damage in many suburbs . The storm produced hailstones of up to 9 cm (3.5 in) in diameter and resulted in insurance losses of around A $1.7 billion in less than five hours . </P> <P> In February 2010, Sydney received some of the highest rainfalls in 25 years with 65 mm (2.6 in) of rain falling in one night at Observatory Hill . In the first weeks of the month, some suburbs were hit by thunderstorms which brought heavy rain and gusty winds which cut out power and damaged homes . The heavy rain was caused by remnants of ex-tropical Cyclone Olga and humid north - easterly winds feeding into the low pressure trough . 2010 was an overly wet year with the cloudiest October and the third cloudiest July on record . In 2011, Sydney recorded its wettest July since 1950 . The CBD recorded 244 mm (9.61 in) of rain that month . 2011 was also the wettest year since records began in 1858 . </P> <P> On 18 November 2013, a tornado hit Hornsby, a suburb in the Upper North Shore . The tornado's path was 2 km (1.2 mi) long and 50 m (160 ft) wide . The tornado blew off roofs and toppled large trees . The winds in the tornado reached 140 kilometres per hour (87 mph). A total of 12 people were injured in the tornado . </P>

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