Areas worst affected will be the NSW mid-north coast, the Hunter, Sydney, as well as the Illawarra and south coast regions.
Alpine areas above 1200 metres in the southern tablelands, south-west slopes and the ACT will also be lashed by the storm.
Widespread damaging winds and locally destructive gusts of up to 125km/h in some coastal areas, as well as flash flooding, are expected later today.
The developing low pressure system off the NSW coast is expected to intensify and move closer to the coast later today.
Winds on the south coast, Illawarra, Sydney, Hunter, mid-north coast and alpine areas of the southern tablelands, south-west slopes and ACT are expected to average more than 65km/h.
Peak wind gusts are expected to exceed 90km/h.
Locally along the coastal fringe, winds could average in excess of 90km/hour, with gusts in excess of 125km/hr.
Blizzard conditions are expected to develop this afternoon or evening in Alpine areas of the southern tablelands, south west slopes and the ACT above 1200 metres.
Heavy rainfall leading to flash flooding is possible on the south coast, particularly in the far south.
Emergency services has advised people to keep clear of fallen power lines, stay indoors away from windows and keep children indoors.
Emergency services has advised the public not to walk, ride a bicycle or drive through flood water, and keep clear of creeks and storm drains.
The National Parks and Wildlife Service recommends that people consider postponing back-country travel until conditions improve.
For emergency help in floods and storms, ring the SES (NSW and ACT) on telephone number 132 500.
The next warning is due to be issued by 9.30am today.
A number of gale and wind warnings are also current for NSW coastal waters.
On the south coast, a gale warning is current from Gabo Island to Moruya, with seas rising up to five metres on a rising to three- to four-metre swell.
A gale warning is also current for the Sydney's closed waters, Pittwater, Port Jackson and Botany Bay, with waters becoming very rough.
Storm force winds are expected from the mid-north coast south along coasts in the Hunter, Sydney, Illawarra, to the south coast - from Seal Rocks to Moruya.
A strong wind warning is current for the far north coast, from Tweed Heads to Smoky Cape and from Smoky Cape to Seal Rocks.
Huge seas rising up to six metres on three to four metre swells will batters coasts tonight.
©The Australian
THE NSW State Emergency Service has urged residents in coastal NSW to take extreme care during storm conditions forecast for tonight and tomorrow.
Emergency services along the Eastern coast of NSW are bracing themselves for the worst tonight with a cyclone in the Tasman Sea expected to pass close to land from midnight.
Winds in excess of 100 kilometres an hour are predicted to scour the coast between the Hunter Valley and the Illawarra, easily powerful enough to cause widespread property damage.
A spokesman for the State Emergency Service said the organisation had around 500 people on standby along a stretch of coast ranging over a few hundred kilometres.
"We're just basically watching the whole of the South Coast. We've got no feeling for this whatsoever, so we'll be up all night watching what is happening. Really we can't react until we know what we are reacting to," he said.
Mike de Salis, of the Bureau of Meteorology said exposed areas of the coast, such as Ulladulla and south east Sydney, would bear the brunt of the storm, which is expected only to dissipate after midday tomorrow.
"The actual weather system itself is not going to come on shore but will stay in the Tasman. Its effects will be very clearly felt," he said.
The SES advises people to stay indoors and away from windows during the storm.
People who must be outside are warned to keep clear of fallen trees and power lines, never walk or drive through floodwater, and stay clear of creeks, storm drains, culverts and causeways.
The storm also will make beaches dangerous, and people are warned to stay out of the sea and any areas exposed to surf.
The SES is advising residents to prepare for the storm by securing or putting away any loose items around their homes, and moving vehicles under cover and away from trees.
Boat owners should ensure their vessels are properly secured.
Both the weather bureau and the SES are advising people to listen to radio stations for weather warnings and updates, which will be issued regularly today.
©The Australian