Heavy rain, storms to batter Australia's southeast

Days of heavy downpours have polluted dozens of beaches around Melbourne's Port Phillip Bay, while rain is set to increase across eastern NSW and southeast Queensland later in the week.

The Bureau of Meteorology's Dean Narramore says thunderstorms will develop in southern and south-eastern Queensland on Wednesday with rain increasing across the NSW coast and further south.

A cold front is also expected to spread into southern Queensland and northern NSW, spreading state-wide by Friday.

"Rain and thunderstorms will intensify throughout the week with possible flash flooding, strong winds and widespread heavy rain," he told AAP.

The NSW State Emergency Service also anticipates a flurry of requests for help as the trough moves through the state.

Wet weather will track along the east coast.

Communities in the New England and Northern Rivers regions, and along the northern half of the mid-north coast, should expect widespread showers of 30mm to 50mm and up to 100mm in some areas.

The bureau is forecasting the trough will deepen on Friday and potentially develop into a low-end east-coast low, impacting the NSW mid-north coast before shifting to the Hunter, Sydney, Blue Mountains and Illawarra by the evening. 

"That may bring damaging winds, heavy rainfall and dangerous surf to much of the coastal area," meteorologist Sarah Scully said.

The weather system is expected to move south on Saturday to the Illawarra and NSW south coast, bringing heavy rainfall, strong to gale-force winds and hazardous surf. 

NSW SES assistant commissioner Sean Keans urged east coast, Blue Mountains and metropolitan Sydney communities to prepare for poor weather by cleaning gutters, trimming trees and branches and securing loose items around homes.  

"We still have a few days until the weather may deteriorate, so it's a good time to make sure you take steps to prepare your homes," he said. 

Emergency assets and crews have been pre-positioned ahead of the forecasted wild weather, Mr Keans said.

"Flood and storms teams are on standby to respond should they be required, but we're pleading with the community to be prepared, stay informed and not drive through floodwaters."

The warning comes after Melbourne was hit by the equivalent of one month's rain on Monday, while some parts of Victoria recorded rainfall not seen for more than 150 years.

Severe storms with heavy rain are also possible for Queensland's Scenic Rim, Border Ranges and southern Downs on Wednesday afternoon and into the evening.