Heavy Rain Coming For Fire Grounds But Could Trigger Flash Flooding, Landslides

The promise of much-needed rain for fire-ravaged parts of the nation's southeast has triggered warnings about the potential of flooding and water quality issues.

From Wednesday, showers and storms will begin to sweep through eastern Australia, with the Bureau of Meteorology forecasting heavy rainfall to fall across areas of NSW and Victoria that are still burning.

Bureau meteorologist Sarah Scully said there has been a real shift in weather patterns over the last week and the latest changing weather is being prompted by a deepening inland trough that is drawing humid air across the east.

"The hit and miss nature of storms means it's difficult to forecast the exact location of the heaviest rainfall totals," Scully said.

"But the storms that do form are likely to be slow-moving, bringing the potential for heavy rainfall."

According to the Bureau, central Victoria will have its peak shower and storm day on Wednesday, while Thursday will see widespread activity across eastern parts of both NSW and Victoria.

Central parts of Victoria could see around 5-15 mm of rain on Wednesday with showers and storms, but isolated heavy storms could potentially bring as much as 50mm in some parts.

On Thursday the storms will push towards eastern Victoria, more likely towards the eastern ranges with forecast rains of up to 12mm, the Bureau said.

In NSW unsettled weather is most likely to impact the southeast and east of the state.

Fire-ravaged parts of the state's south including the Snowy Monaro and the southern highlands will see the majority of thunderstorm activity from Thursday.

Parts of the north-east will also be impacted and could see isolated falls above 80mm as well.

A sky crane water bombing helicopter flies over the town of Wandandian south of Nowra. Image: AAP

The wet weather is expected to stick around throughout the weekend and into Monday with widespread accumulated totals forecast to reach up to 80mm in some parts while other areas could see daily totals in excess of 50mm thanks to slow-moving thunderstorms, Scully said.

"Hopefully, some of this heavy rainfall will fall over fire sites and help control and even extinguish some of those fires."

But Scully warned while the showers are good news for exhausted firefighters and communities who are continuing to be impacted by blazes in both states, the heavy rains could be a "double-edged sword".

"Heavy rainfall and gusty thunderstorms bring the potential for flash flooding particularly in burnt-out areas of NSW and Victoria which are now vulnerable to landslides and trees coming down," she said.

The burnt landscape lining Benalong Road, south of Nowra. Image: AAP.

It's also prompted a health warning from the NSW government which aired concerns over water quality with the potential for ash, dust, dead birds, fire retardants and other debris material to be washed into tanks.

NSW Health said while the presence of ash and debris in rainwater is unlikely to pose a health risk, it could affect the appearance and taste.

"Fire retardants currently used in Australia are of low toxicity, but may also affect the appearance and taste of rainwater," its website said.

"If you are concerned that your rainwater tastes, looks or smells unusual, or you suspect your rainwater has been contaminated, an alternative safe water supply, such as bottled water, should be used for drinking, preparing food or ice, cleaning teeth and given to animals until your tank can be cleaned and refilled."

By Wednesday morning all blazes across NSW had been downgraded to an advice level, including three in the state's south which had been burning at watch and act level on Tuesday.

In Victoria, one fire in Tamboon was still burning at emergency level on Tuesday night and six others remained at watch and act level.

An air quality alert also remains in place in the state after parts of Victoria were shrouded in smoke on Tuesday.



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