Australia’s weather will serve up a smorgasbord of variability this weekend, including another bout of heavy rain for the eastern seaboard.

The soaking thankfully won’t match the intensity of early April, but a separate weather system will also bring heavy rain to far north Queensland, while a tropical low threatens to intensify into a late season cyclone in the Gulf of Carpentaria.

Clear skies will prevail across the rest of Australia this weekend but with a vastly different feel — southern states will rug up through frosty nights, while Western Australia’s incredible run of unseasonable warmth heads into record territory.

Overnight temperatures will fall to single digits in southern parts of South Australia.(Supplied: Gary Mansell)

Stormy week culminates in weekend drenching for east coast

The storm season ends in less than a fortnight, but this week has brought an unseasonably active outbreak of thunder and lightning to NSW, and occasionally southern Queensland.

While thunderstorms eased on Friday, the stormy skies are now being replaced by a broad rainband across south-east Queensland, along with heavy showers along the NSW coast.

The rain will result from a similar set-up to the previous deluge – a humid airstream off the Tasman and Coral seas clashing with a mass of cold air over the inland.

But thankfully a repeat of the severe floods which ravaged Sydney and the Illawarra is unlikely due to a low pressure system forming well offshore, as opposed to a fortnight ago when a low developed right on the coast.

The heaviest falls will arrive from Saturday to Monday from about Rockhampton to the Gold Coast where totals could exceed 100mm, potentially enough to trigger a few pockets of minor riverine flooding, and possibly very isolated flash flooding.

Brisbane can expect rain to develop on Saturday, persist on and off through Sunday, before easing on Monday, and is likely to pick up anything from about 20 to 80mm — the uncertainty due to the city’s location on the southern periphery of the system.

For NSW, the heaviest falls this weekend will impact the northern half the coast where more than 50mm could accumulate.

Sydney’s wettest day will be Saturday when up to about 20mm could fall across coastal suburbs.

Only a few millimetres should fall over western suburbs of Sydney, however Penrith has already received 264mm this month — more than five times the average and the wettest April in 36 years.

Bureau monitors tropical low and issues flood watch for north Queensland

Like the thunderstorm season, the northern wet season also wraps up in less than two weeks, but a weak tropical low has formed over the Arafura Sea and is showing signs it could develop further this weekend.

The bureau currently indicates there is only a 10 per cent chance the low will deepen into a cyclone, however regardless of the system’s status, its movement is still of critical importance.

Thankfully for the flood weary north, a track slowly west is forecast this weekend, perhaps clipping the far north-east tip of the NT – a path which would avoid inland penetration and a subsequent heavy rain across tropical catchments.

Cyclone numbers have declined in recent decades due to climate change.(ABC News)

Even including the unlikely addition of another system, the 2023-24 season will finish with below average cyclone activity in Australian waters, continuing the trend of declining numbers through the past few decades.

This season has produced eight named storms so far, comfortably below the annual average of 11 cyclones either forming or moving through Australia waters.

The last time an above average number of cyclones occurred was 18 years ago, with 12 recorded in 2005-06.

The drop in cyclone numbers this century is the result of climate change shifting the structure of broadscale tropical circulations, despite the warmer waters providing extra energy to fuel stronger systems.

The official season ends on April 30, although occasionally cyclones do develop in the dry season – typically well-off Australia’s northern coastline.

Heavy rain is possible over Cape York and the far north-east tip of the NT this weekend.(ABC News)

In the meantime, a moist easterly could bring up to 100mm in 24 hours to north Queensland, prompting a flood watch for the northern and eastern Cape York peninsula north of the Mossman River.

The flood threat is being enhanced by wet catchments following hundreds of millimetres already falling this week from Innisfail to Cooktown.

Wintry nights to bring the first frost of 2024

This April is on track to break a run of 10 consecutive warmer than average months for Australia – mostly due to below average temperatures across central and southern regions.

The autumnal chill is due to high pressure systems sitting nearly permanently to the south of WA.

Winds spin anticlockwise around highs and the result has been cool southerly winds blowing on most days from the western interior to the Great Dividing Range.

Cool weather will continue for south-east Australia this weekend, especially at night as clearing skies and light winds provide the optimal conditions for low overnight temperatures.

South-east Australia will wake to Sunday morning temperatures well below 10C and near freezing along the ranges. (ABC News)

Minimums will fall to single digits across Victoria, Tasmania and southern parts of SA and NSW, and fall close to freezing along the ranges.

Melbourne and Adelaide can expect the coldest temperature so far this year between Saturday morning and Monday, and while a brief spell of warmer northerly winds will arrive during Monday and Tuesday, cool southerlies will again return to southern states by midweek.

The year without an autumn — Perth baking in endless heat

The last six months has been the warmest and driest on record for western parts of WA.

From October to March, Perth received just 22mm of rain, easily below the previous record of 39mm in 1892.

During the same period the city’s average maximum temperature has been 30.7 degrees Celsius, an incredible 3.4C above normal and also a record.

This April has only prolonged the trend with Perth’s highs averaging 30.0C, a full 5C above normal and 5C above Taree’s temperatures at the same latitude on the east coast.

From October to March, Perth has received just 22mm of rain.(Supplied: Jeroen Gerritsen)

The record dry spell also continues – the city’s rain gauge has collected just 1mm this month, well short of the April average of 43mm.

So if eastern Australia is relatively cool and wet, why then does Perth’s weather still resemble summer?

A quick glance through daily weather maps during the past few months supplies the answer – the pressure south of WA has been 5 hectopascals above average for six months.

In other words, high pressure systems have been favouring a position which ensures winds across WA are from the east, carrying dry desert heat from the interior to the west coast.