As today's early forecasts predicted, it's absolutely pelting down in Melbourne this Friday.

Rain began falling in the city just before 8 am on Friday morning, with 3.6 mm in the gauge by 9 am.

Rain gauges "reset" at 9 am, because daily observations are taken in the 24-hour period from 9 am. Between 9 am and 12:30 pm, a further 39 mm of rain had fallen in the city, with at least another hour or so of rain expected before skies clear temporarily.

Why such heavy rain in the middle of summer?

"Tropical moisture is feeding into a low pressure trough," Weatherzone meteorologist Ben Domensino explains. "That's why we're seeing such high rainfall rates."

Melbourne's wettest ever January day was 108 mm. That record won't be threatened by the current rainband, which is moving from west to east and appears likely to pass through the city by early-to-mid afternoon.

However thunderstorms will likely move across western and central Victoria tonight, so there's a chance of more heavy rain this evening.

While the Melbourne downpour has caused traffic chaos on some roads, there are no reports yet of serious flooding. Locals, sensibly, have taken to the laneways to drink the world's best coffee until the weather clears.

Nothing better than a coffee on a rainy day. #melbournemoment #melbourneweather pic.twitter.com/LPLH2pFA06

— Segovia (@coffeesegovia) January 29, 2021

Meanwhile, farmers have rejoiced at the widespread unseasonal rain across Victoria as well as parts of western New South Wales overnight.

It also continues to rain in Sydney – albeit much more lightly – due to a moist onshore easterly flow.

The general weekend outlook remains damp for Sydney, with a chance of showers on both Saturday and Sunday. Melbourne should dry up after some showers on Saturday morning.