Long overdue rain is finally on its way to Queensland and NSW – but forecasters warn it might be too much of a good thing, with some areas set to get their heaviest February rainfall in decades.

South-east Queensland is set for a drenching, with as much as 200 millimetres of rain along the coast on Wednesday and Thursday.

Rain is also forecast for Queensland’s drought-affected southern interior and south-west, with the Southern Downs, Darling Downs and parts of the Warrego and Maranoa regions getting up to 40 millimetres a day until the weekend.

In NSW, falls of about 25 millimetres are expected from Lismore in the north to Cooma in the south, and about 10-15 millimetres further inland to Bourke. The state’s far west could receive between up to five millimetres.

The rain will come from a large high pressure system over the southern Tasman Sea that will direct moist easterly winds onto eastern Australia.

“Many of the fires that we had earlier in September and October in northern NSW will see this widespread rainfall,” Bureau of Meteorology spokesman Dean Narramore said.

“It looks like even many of the ongoing fires to the west of Sydney and down towards the south coast and into East Gippsland will also get some of this rainfall as well.”

Please, please, pretty please! (8 day rainfall outlook) #NSWRFS pic.twitter.com/4QZvhu58cs

— NSW RFS (@NSWRFS) February 4, 2020

Mr Narramore said there would also be a surface trough in central parts of Queensland and NSW.

“That’s going to combine with this persistent, very moist onshore tropical flow coming in off the Coral and Tasman seas to produce widespread afternoon and evening showers and thunderstorms every day from Wednesday, right through to early next week,” he said.

The rain will put eastern and northern NSW at particular risk of flooding after days of rain and thunderstorms.

“Flash flooding will become quite a risk, particularly if we get these storms over the same areas day after day,” Mr Narramore said.

“As we get into the weekend and early next week, we could even possibly see riverine flooding for some parts of New South Wales as well, and even possibly in the southern parts of Queensland.”

Severe Weather Update: heavy rainfall and potential flooding for NSW & QLD.

Video is current at 11 am AEDT 5 February 2020.

For the latest weather and warnings, information visit https://t.co/ZwwnxWJFoM and follow advice from emergency services. pic.twitter.com/uBjtCUaEut

— Bureau of Meteorology, Australia (@BOM_au) February 5, 2020

The BOM is keeping a close watch on a tropical low near the Northern Territory-Western Australia border.

“That’s going to move over the Kimberley in the coming days and then that’ll move offshore midweek, possibly developing into a cyclone as we get towards the end part of this week,” he said.

There are flood watches for the Northern Territory and parts of Western Australia as a result.

Meanwhile, soil damaged by fire and years of drought will be at risk of being washed away, potentially affecting runoff to dams.

A similar set-up in mid-January brought severe hailstorms up and down Australia’s east coast, but Mr Narramore said this system was not quite as unstable and would be less likely to produce widespread damaging hail.

However, drought-stricken areas of western NSW will remain parched despite the forecast high rainfall. Bureau of Meteorologist climatologist Blair Trewin said the rain would be concentrated in NSW’s coastal areas.

“It’s going to be a significant rainfall event across the state but the extreme west will not pick up too much,” Mr Trewin said on Wednesday.

“Most western rainfall activity will be concentrated around the northern inland area, particularly along the NSW-Queensland border.

“The [rainfall] deficits are very big, so it certainly won’t go very far. But it’s better to have it than not have it.”

Mr Trewin said three years of dry cool seasons had resulted in limited rainfall, meaning drier waterways and rivers and low water storage levels.

“Evaporation during the cooler season is lower and it looks like this upcoming season outlook is going to be slightly towards the drier side again, which will not be good for sustainability of the land,” he said.

“Dry land crops could be decent but a dam for example would need a lot more rain to fill.”

-with agencies