At least one month’s worth of rain is expected to sweep the east coast in two days, with areas of northern Queensland likely to get almost three times their monthly average, the Bureau of Meteorology (BOM) says.

BOM extreme weather senior forecaster Scott Williams told The New Daily that it will begin raining on Wednesday night and continue for 48 hours through to late Friday and early Saturday.

He said the slow-moving pressure trough will travel from coastal towns into inland western parts of New South Wales and Queensland, down to Victoria and eventually reach as far south as Tasmania by Saturday.

“Brisbane is the city likely to receive the most rain, from 50 millimetres up to 75 millimetres, as well as the Gold Coast until early Saturday,” Mr Williams said.

“Canberra should get about 30 millimetres, while Sydney and Melbourne will get up to 20 millimetres before clearing late Saturday morning.

“The northern half of Tasmania will receive about 50 millimetres with some isolated totals of up to 100 millimetres, which is pretty substantial. That shouldn’t clear until Sunday morning.”

The BOM has issued a flood watch for Queensland from Tully (just south of Cairns) to Gladstone, including Townsville, Mackay and Rockhampton.

Mr Williams said the Queensland towns of Mackay, Townsville, Moranbah and Rockhampton would likely be the hardest hit.

Late-week soaking looms for eastern Australia: https://t.co/qH4VMuUUgy pic.twitter.com/nRONvjY1sq

— Weatherzone (@weatherzone) May 15, 2017

The northern parts of the state are expected to receive widespread rainfall with 100 millimetres to 200 millimetres starting Wednesday night — two to three times the typical May average rainfall.

Residents of Townsville and Moranbah usually expect an average of 32 millimetres of rain in May.

Meanwhile, southwestern Queensland is bracing for heavier, isolated falls with thunderstorms forecast during Thursday and Friday, according to the BOM. A possible 25-60 millimetres is expected.

Mr Williams said western inland areas of NSW and parts of Victoria, including Swan Hill and Bendigo, will face at least the monthly average, but possibly double that.

Inland NSW will bear the brunt of the weather system come Thursday, with isolated areas expecting up to 100 millimetres of rain, while the Far West region, including Bourke and Wagga Wagga is expecting 50 millimetres.

Sydneysiders will likely miss out with up to 10 millimetres expected over the next few days, as will Melburnians with the CBD area likely to receive just one millimetre in total.

The northwest of Victoria will be a much different story where the BoM is anticipating 25-50 millimetres.