Tuesday 21 April 2015

Three confirmed dead as floods and cyclonic winds hit New South Wales.

Three people are reported to have died in the town of Dungog in New South Wales, as cyclonic winds hit the Hunter, Central Coast and Illawarra Regions of New South Wales on Monday 20 April 2015. Dungog appears to have been the worst hit town in by the storms, with reports of winds gusting at 135 kilometers per hour, 312 mm of rain falling in 24 hours and houses being washed off their foundations by floods. The bodies of two men and one woman have been found in the town to date, and it is possible that the death toll will rise as the situation becomes cleared. At the moment there is reportedly no mobile phone reception in the town, and most of the landlines have also been destroyed.

Flooding in Dungog, New South Wales on 21 April 2015. Higgins Storm Chasing/9 News.

Elsewhere in New South Wales around 200 000 homes and businesses have been left without power in Newcastle, Sydney and the Hunter and Central Coast Regions. Floods and building collapses have been reported across the affected area, with most towns and cities still on high flood alert. All transport networks severely affected, with many roads closed, reports of a school bus being washed off a road at Martins Creek and ships trapped outside Sydney Harbour. Many schools are also closed across the region, with some being used as evacuation centers in the worst affected districts.

Storm surge battering the iconic Bondi Beach. Brendon Thorne/Getty Images.

Cyclonic storms form due to heating of air over the sea, usually in tropical zones. As the air is heated the the air pressure drops and the air rises, causing new air to rush in from outside the forming storm zone. If this zone is sufficiently large, then it will be influenced by the Coriolis Effect, which loosely speaking means the winds closer to the equator will be faster than those further away, causing the storm to rotate, clockwise in the northern hemisphere and anticlockwise in the southern hemisphere.

Flooding in East Maitland, New South Wales. Eleshia Howell/The Newcastle Herald.

Whilst the high winds associated these storms is extremely dangerous, the real danger from such storms is often the flooding. Each millibar drop in air pressure can lead to a 1 cm rise in sea level, and large storms can be accompanied by storm surges several meters high. This tends to be accompanied by high levels of rainfall, caused by water picked up by the storm while still at sea, which can lead to flooding, swollen rivers and landslides; which occur when waterlogged soils on hill slopes lose their cohesion and slump downwards, over whatever happens to be in their path.

See also...

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