WHAT IS AN EAST COAST LOW?
* Intense low-pressure system that forms close to the NSW coast in the Tasman Sea.
* Drives high winds, heavy rain and dangerous surf into NSW coastal areas. Can be felt in southern Queensland and far eastern Victoria.
* Most frequent in autumn and winter, and particularly June.
WHY EAST COAST LOWS CAUSE BAD WEATHER
* Draws strong, moisture-laden wind across the coast, causing heavy rain when it is uplifted by hills and ranges that run parallel to the coast.
* Sits close to the coast and fed by temperature differences between the warm Tasman Sea and cooler air over land.
* When the gap widens at night between temperatures on land and at sea, east coast lows can intensify.
ARE THEY DANGEROUS?
* Gales or storm-force winds can damage buildings, fell trees and powerlines, cause powerful surf that can damage the coast and, in some cases, run ships aground.
* Can cause flash flooding and riverine flooding.
OTHER EAST COAST LOWS
* April 2015: Four dead, 20,000 calls for assistance across NSW. Worst-affected areas in the Hunter region. Reports of 312 millimetres of rain in 24 hours near Dungog.
* June 2007: Bulk carrier Pasha Bulker runs aground near Newcastle amid wind gusts of up to 124 kilometres per hour.
* October 2004: Mean wave heights of five metres off Sydney, with a maximum height of about 10m.
* August 1998: More than 300mm of rain over four days in Sydney and Illawarra, 420mm at Beaumont and 401mm at Kangaroo Valley.
* May 1974: Gusts of 165km/h at Newcastle's Nobbys Head. Bulk carrier Sygna runs aground.
* August 1857: The Dunbar wrecked at South Head - 121 dead and one survivor.
(Source: Bureau of Meteorology)
© AAP 2019