Fox News Weather Center

Flooding Rain Threatens Both Coasts of Australia

Weakening Tropical Cyclone Quang and a non-tropical system will threaten opposite coasts of Australia with heavy rain into Saturday.

Quang will target Western Australia, around Learmonth Royal Australian Air Force base, with torrential rain and gusty winds. Meanwhile, the non-tropical system will spread heavy rain down the southeastern coast of Queensland to the northern coast of New South Wales.

Tropical Cyclone Quang

Tropical Cyclone Quang reached its peak intensity on Thursday, local time, with maximum sustained winds of nearly 215 kph (135 mph). That made Quang's strength equivalent to that of a Category 3 major hurricane in the Atlantic or eastern Pacific oceans.

Disruptive wind shear (strong winds above the surface) have since increased around Quang, causing the cyclone to weaken. That trend will continue as Quang approaches the Australian coast.

Quang is expected to make landfall early Saturday morning, local time, with its strength equal to that of a tropical storm or depression. Regardless, conditions will deteriorate later Friday into Friday night as Quang approaches.

"The main threat from Quang will be heavy rain and flooding," stated Senior Meteorologist Jason Nicholls.

From later Friday through Saturday night, a general 25 to 75 mm (1 to 3 inches) of rain will spread across Western Australia.

"There will be local amounts of 75 to 150 mm (3 to 6 inches) along the coast from Exmouth to Cape Cuvier," added Nicholls. The majority of this heavier rain will pour down prior to Saturday afternoon.

The coastline in the vicinity of where Quang comes onshore will also be subject to wind gusts of 65 to as high as 95 kph (40 to as high as 60 mph) Saturday morning. Extremely rough seas off the coast will create dangers for boaters.

Heavy Rain Targeting East Coast

While Quang approaches the state's western coast, a non-tropical storm system will spend the time into Saturday dropping heavy rain southward from the coast of southeastern Queensland to the northern coast of New South Wales.

Rain will fall heavily at times, especially in coastal areas from Brisbane to north of Sydney. Some of these areas experienced flooding rainfall less than 10 days ago as 250-500 mm (10-20 inches) of rain fell over a several-day period.

While this storm will take a similar track and impact many of the same areas, one big difference is that the widespread damaging winds that accompanied the first storm will not be common this time.

This will greatly limit the threat for power outages, after the previous storm resulted in more than 200,000 homes to be without power at some point during the event.

While damaging winds are not expected to be a widespread problem, heavy rain will once again result in an elevated risk for flooding. Rainfall will average 25-75 mm (1 to 3 inches) from near and north of Sydney to Brisbane with localized amounts up to 150 mm (6 inches) possible. This amount of rain falling in a short time period can cause flash flooding, especially on small streams and in urban areas.

The heaviest rain will fall across southeast Queensland into Friday, including Brisbane and the Gold Coast.

The worst of the storm will then shift farther south to start the weekend as torrential rain falls along the northern coastline of New South Wales. Sydney will be spared the worst of the storm; however, rain will still pour down Saturday into Saturday night.

As the storm continues to move southward, the heaviest rain will shift off the coast by Sunday; however, rivers will likely remain high resulting in dangerous conditions across parts of eastern New South Wales.