ONE of the hottest November months in Australia’s history is about to come to a screeching halt with warnings of a “major rain and flood event” sweeping through the country’s east.

Victorians are bracing for flooding with storms set to dump 300mm of rain in parts of the state over the next few days while parts of NSW are also on alert for “more than a month’s rain in 36 hours”.

Flash flooding is likely in Melbourne as a low-pressure system dumps up to 150mm of rain on the city between Friday and Sunday, while falls in Victoria’s northeast could top 300mm.

The storms will develop in the far west late on Thursday before extending across the rest of the state on Friday.

The Bureau of Meteorology has called it the “most significant rain event for many years” and issued a series of weather warnings as the big wet approaches.

“This is a very, very big weather event, we are in uncharted territory,” senior meteorologist Scott Williams told reporters on Wednesday.

“We could see six-hourly rain rates of over 100mm over several parts of the state, stretching from the Grampians and Horsham in the west to the northeast and ultimately Melbourne.”

Severe Weather Warning for heavy rainfall has been issued for the whole of #Victoria. Heavy rainfall expected to start in the far west Thursday night, extending across the State during Friday and Saturday. Check the details and other warnings at https://t.co/ipm9yXcTlp pic.twitter.com/yqPMlCcTUs — Bureau of Meteorology, Victoria (@BOM_Vic) November 29, 2017

More than a months rain forecast in 36 hours in some areas to start our summer. Check the #forecast at https://t.co/SrkQxr8aaY pic.twitter.com/gb9i8dBbYt — Bureau of Meteorology, New South Wales (@BOM_NSW) November 29, 2017

More than 100mm of rain could fall in a band encompassing capitals from Brisbane all the way down to Hobart with meteorologists forecasting of a “month’s worth of rain in just a few days for some regions”.

Almost 30mm has fallen in Brisbane yesterday and a severe weather warning for thunderstorms is in place for much of the state’s coast.

In some areas 200mm of rain could wash down in the next few days, almost certain to lead to flooding.

But that’s later this week — first we’ve got to get through an absolutely scorching few last days of spring.

Adelaide CBD reached a whopping 39.4C yesterday, its hottest day since March.

Shane Warne was suffering under the South Australian heat, tweeting it was already past 30C at 9am.

Melbourne’s 35.8C on Wednesday (the same is expected today) would be the city’s warmest day since last summer. Hobart will get to 33C today, which will be the hottest day in the Tasmanian capital for two years.

“This is a huge week of weather,” Sky News meteorologist Tom Saunders said.

“Before the rain arrives, southeast Australia is ending one of the hottest Novembers on record with another spell of extreme heat.”

Mr Saunders said the unprecedented heat had been due to a blocking high over New Zealand which could be the result of weak La Nina conditions forming over the Pacific.

Last week, the Bureau of Meteorology said it was likely a La Nina weather system would indeed form, but it would not be as strong as previous years.

Morning ! Gym time & it’s already 30 degrees 😩😩😩 https://t.co/nt5hOyFdb3 — Shane Warne (@ShaneWarne) November 28, 2017

Then, as December hits, temperatures will plummet as the heavens open.

“South east Australia can expect a major rain and flood event later this week,” Mr Saunders said.

The forecast is based on the likely outcome of what’s expected to be a weather battle royal.

Heavy rain & storms developing over southeastern Australia over the next few days. Stay safe & check latest warnings here: https://t.co/fwzkaAMOMs pic.twitter.com/T4e06WbZna — Bureau of Meteorology, Australia (@BOM_au) November 29, 2017

#VICStorms outlook for Thursday. Severe thunderstorms are likely in southwestern #Victoria tomorrow, with heavy rain, large hail and damaging winds possible. Check the forecast: https://t.co/5xUUDhCgRH pic.twitter.com/0ckEMXVqg2 — Bureau of Meteorology, Victoria (@BOM_Vic) November 29, 2017

Very warm and humid northerly air that has drifted over southeast Australia, bringing the current heat, looks like it will clash with cold air moving north from the Southern Ocean.

“Warm air colliding with cold air is a volatile mix and will lead to the formation of a deep and complex low pressure system over southeast Australia on Friday,” Mr Saunders said.

“The low will remain in the vicinity of southeast Australia until early next week and lead to well over a month’s worth of rain in just a few days for some regions,” he said.

Between tomorrow and next Wednesday, Brisbane could get smashed with more than 100mm of rain, only slightly below the December average of 128.4mm.

Umbrellas at the ready Melbourne and Canberra, you could see anything from 50-100mm of rain where between 50-60mm in the entire month is more usual.

A sodden Sydney and Hobart look like they will receive 50mm in a week, close to the month’s average. Even Adelaide’s relatively modest prediction of between 25-50mm would still be a month’s rain in a week.

“The rain will lead to both flash flooding and river flooding with northeast Victoria most at risk where up to around 200m is possible from this event,” Mr Saunders said.

WHEN WILL THE RAIN HIT YOU?

ADELAIDE

An incredibly hot 38C on Wednesday, dipping to 31C on Thursday and then a big drop to 21C on Friday. The end of the week could see the biggest rainfalls.

MELBOURNE

It will reach 35C on Thursday with the heavens due to open on Friday with up to 25mm in just one day. Expect a high of 26C as Melbourne heads into the weekend but that will plummet to just 20C on Sunday as the rain continues.

HOBART

This has been the hottest November in Hobart since records began. Tasmania’s hot run continues until Thursday when the mercury will peak at 33C. Friday will then see the mercury drop by 10C to 23C with up to 25mm of rain. Possible rain throughout the weekend with highs of around 17C.

CANBERRA

A high of 30C on Thursday dipping only a touch to 29C on Friday with storms a possibility. But it’s Saturday that’s going to be really wet. Up to 60mm of rain could fall with the dial getting to 23C. Temperatures will then continue to drop further with further rain into next week.

SYDNEY

Unlike further south, temperatures will remain relatively stable in Sydney with 27-29C throughout the weekend. The sun will remain up to the weekend and then the clouds will come with up to 20mm of rain falling on Saturday and storms next week.

BRISBANE

It’s already raining in Queensland. The rest of the week and weekend will see temperatures of around 29C with rain possibly every day. Up to 25mm could fall on a stormy Monday.

DARWIN

34-35C across the Top End with sunshine and storms but rainfall below the other capitals.

PERTH

Never one to play the east coast’s game, Perth will be a model of summertime weather this weekend. Clear skies every day, temperatures will rise from a mild 25C on Thursday to 36C on Sunday.

benedict.brook@news.com.au | @BenedictBrook