the weather system is called an east coast low . it is formed from low-pressure over the tasman sea .
they draw strong , moisture-laden winds across the coast , which cause heavy rain to fall .
they are particularly common in june and can dump hundreds of millimetres of rain .
they usually move away after 12 hours but this one is going to stick around for 24-36 hours .
east coast lows were common in the 1970s but became less common in the 90s .
` close to the coast winds are up to 135kmh and rain up to 200 mm , ' weatherman don white says .
police and nsw fire and rescue have been called in to help the ses on 2800 weather related call-outs .