Flooding and crop devastation predicted as 'severe weather' set to pummel eastern Australia

Dangerous thunderstorms are set to cause large hail and flash flooding, destroy crops and drive deadly spiders into homes across large swathes of eastern Australia over the next week.

Triggered by a low pressure system forming over the southern centre of the country and a trough across eastern Australia, the hazardous weather will escalate when the two systems combine on Friday, with the added tropical moisture present as a result of La Niña contributing to the severity of the storms.

The Bureau of Meteorology is expected to issue “plenty of severe weather warnings” stretching from Australia’s Top End down to Tasmania, and from parts of South Australia to the country’s east coast, according to bureau meteorologist Dean Narramore.

New South Wales residents should also be on alert for funnel web spiders, according to Australia’s Reptile Park, which issued a warning that the wet weather conditions and warm temperatures create “perfect conditions” for the deadly spiders to breed and “thrive” in gardens and homes in Sydney, Newcastle and the Central Coast.

Related: La Niña set to bring cooler weather, more rain and cyclones to Australia

Meanwhile, in Western Australia, the weather bureau issued a catastrophic fire warning for the state’s interior state on Thursday, while the risk level in the East Pilbara was extreme.

Narramore told Guardian Australia the storms would reach their climax on Saturday, when “very heavy rainfall, damaging winds and large hail” would pound inland areas of Queensland and New South Wales, with “many locations to see 50mm of rain”.

He also warned the storms could wreak havoc across northern NSW and southern Queensland, where farmers are beginning to harvest bumper crops that are up 300% on the previous year of drought. The rainfall is expected to damage grain farming areas at a time when wheat and barley is being harvested.

“There will be some pretty big impacts on the agricultural industry,” Narramore said. “The storms may be so severe, especially with the hail and strong winds, that they may cause some crop losses, as well as hamper harvesting for the coming week.”

Bom is also predicting rain over the weekend in north eastern Victoria to be so heavy that it could lead to flooding, with falls of up to 100mm expected over areas with “already saturated soil”.

While inland areas will see the most severe storms on Saturday, Narramore said the storms will move over east coast cities including Sydney, Brisbane and Melbourne on the weekend, where the front will “linger” for most of next week.

Sydney and Brisbane can expect rain to last into the end of next week, while Melbourne will experience temperatures six to 10 degrees below average.

Related: Australia prepares for bumper harvest as rain boosts NSW winter crops 300%

In a warning to NSW residents, Jake Meney, a reptiles and spider keeper at the Australian Reptile Park, said cool, damp places including laundry, clothes and shoes will attract funnel web spiders.

“If you leave your shoes outside – make sure you give them a tap on the ground before putting your foot in blindly,” he said.

It’s important to stay as calm as possible if bitten by a funnel web spider, he said, and to apply a pressure immobilisation bandage before getting “to hospital as fast as you possibly can”.

Feney also encouraged anyone who can safely catch a funnel web spider to donate it to the reptile park, so it can be milked and antivenom produced ahead of a summer of warm and wet weather – conditions which draw male funnel webs out in search of a mate to breed with.

The impact of La Niña on Australia’s wildlife is also being considered by shark experts, as they look to explain predatory behaviour that has seen more Australians killed in unprovoked shark attacks this year than in any year since 1934.