August is typically one of the driest months of the year for Sydney and much of coastal NSW. This year, though? Not so much.

At the same time, Melbournians are enjoying an unseasonably warm and dry end to winter, with far less rainfall recorded than average.

As it happens, the same factors that are forcing Sydneysiders to reach for their umbrellas are responsible for the blue skies further south.

What’s causing the unseasonal weather?

Meteorological expert Milton Speer, a visiting fellow at the University of Technology Sydney, says there are two key factors at play.

The first is the change of frontal systems which, instead of coming from the west, have been blowing south-east.

“That means they’re actually onshore easterly winds, which hold a lot more moisture going onto the east coast, but they don’t hold moisture over Melbourne, because there’s no moisture source,” Speers told 9news.com.au. 

“The moisture sources are the Tasman Sea and Coral Sea, and the very warm sea surface temperatures that we’re experiencing there for a few years now. And so Sydney has got the moisture in the atmosphere.”

At the same time, climate change is pushing the subtropical jet stream that once typically ran over Brisbane further south, so it’s now bringing rain to NSW

“Sydney just seems to be in the right area… it stays there for a long time because there’s nothing to push it away,” Speers says. 

“That circulation up in the upper levels over northern NSW just stays there and, because of the copious moisture right through the depth of the atmosphere, produces these really heavy downpours and these rain events.”

Just how unusual has the weather been this August?

Sydney typically gets 80.2mm of rain each August. 

This month, it got more than 82mm in a single day alone, and had racked up almost 350mm with more than a week until spring begins.

It also typically only gets seven days with at least 1mm of rainfall. So far this month, there have only been five days that haven’t had any rain.

Melbourne, on the other hand, usually gets 47.7mm and about nine rain-free days in August.

This year, those totals are currently sitting at 18.4mm and 18 days.

Thanks to climate change, yes, Speers says Australia can expect lots more extreme weather, both in terms of periods of hardly any rain and then stretches of deluges.

“So we’ve started to talk about, in recent years, ‘flash droughts’, where you get normal rainfall, or even above-average rainfall for a few months, and then you get nothing,” he says.

Not that that’s what Melbourne’s going through at the moment, with record-low rainfall hitting parts of Victoria since last February.

“Melbourne certainly is a long-term,” he says. 

“From February last year up until end of July or June, they’ve hardly had any; just a small fraction of their annual (average) rainfall or this year.”