Record temperatures are expected over the next week, with some centres sweltering close to 50 degrees.

The conditions will make for the perfect firestorm and authorities are preparing for the worst.

High temperatures, low humidity and strong winds are all coming together to create the sort of deadly combination that brought us the Black Saturday bushfires in 2009.

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Meteorologist Don White from WeatherWatch says the sudden temperature surge has been caused by a lack of rain. Hot air has built up in inland Australia, and now it's being dragged south and east by northerly winds.

"Inland and south Australia are already experiencing the heat, and it is very hot in south-west Queensland and western New South Wales. That very hot air will be moving south-east into Victoria tonight and tomorrow, so Melbourne's temperatures will be into the forties, as well as Adelaide's temperatures tomorrow," White said.

According to Dr Ginni Mansberg during extreme heat, it's important to protect yourself.

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"We know the heatwave is coming, so start hydrating now. So if you normally have two litres of water a day, you would go for 2.5 litres of fluid now so your body's got more hydration on board," Dr Mansberg advised.

"You want to stay in the shade and you want to make sure that you, your children, and even your pets have access to shade, so they can get out of that scorching heat. Make sure your house is cool, so already now draw your blinds, make sure that you're well ventilated and you don't get a hot house before you've started."

The heatwave is expected to last up to a week and temperatures are on average fourteen degrees hotter than the same time last year.

Check the weather forecast for your area

In New South Wales, Sydney's hottest day is forecast to be next Tuesday at 39 degrees - that is eleven degrees above average.

Victoria's hottest day will be tomorrow - with a top forecast of 41 degrees in Melbourne, fifteen degrees above average.

In Queensland, Brisbane's mercury will stay around 29 degrees, while further inland in Birdsville temperatures will peak at 46 degrees.

In South Australia news Monday will be Adelaide's hottest day at 42 degrees - that's thirteen degrees above average. Inland towns like Tarcoola are expected to reach 47.

"The biggest threat is going to be the potential for bushfires, so it is really important, especially in the areas that are prone to bushfires, they they are aware of what's happening and are listening to the media and take relative precautions," White warned.

A guide developed by the Red Cross has the following tips on how to cope with extreme heat.

• Plan your day in a way that allows you to stay out of the heat.
• Ahead of hotter weather, buy a few extra items to make sure you have enough food at home to last over the hot period.
• Think about paying bills online or over the phone.
• Stay indoors or in the shade during the hottest part of the day.
• If you cannot avoid strenuous activity like sport, home improvements or gardening, keep it for cooler parts of the day, such as early morning.
• If you must go out, stay in the shade. Wear a hat and light-coloured, loose-fitting clothes, preferably made of natural fibres. Wear sunglasses and apply sunscreen with a sun protection factor of 30 to exposed skin. If you will be outside for some time, take plenty of water with you.
• Ensure your pets or companion animals are also well hydrated and have plenty of share when they are outside.

• Look at the things you can do to make your home cooler. Install or upgrade insulation in your roof, and install awnings, shade cloth or external blinds on the sides of the house facing the sun. For more advice, talk to a registered building practitioner or visit www.yourhome.gov.au.
• If you can, stay inside, in the coolest rooms in the house.
• Reduce heat from sunlight coming through the windows by using external shades or light-coloured curtains.
• Use an air conditioner, evaporative cooler or fan to keep cool.
• Have your air conditioner serviced before summer.
• Remember, sometimes the electricity fails during heatwaves, so you'll need an alternative way to cool your home.
• Ensure there is sufficient air circulation, either from an air conditioner or by leaving a secured window or door open.
• Take cool showers and splash yourself several times a day with cold water, particularly your face and the back of your neck. A loose, cotton, damp cloth or scarf on the back of the neck can also help you to stay cool.
• Go to an air-conditioned building in your local area to cool off - a shopping mall, community centre, library or swimming pool.

• Drink regularly, even if you do not feel thirsty. Water is the best option.
• Avoid alcohol, tea, coffee and sugary or fizzy drinks. They make dehydration worse.
• Eat little and often rather than large meals. Try to eat more cold food, particularly salads and fruit, which contain water.

For more information download the Red Cross heatwave factsheet.

For more information download the SES factsheet.

This reporter is on Twitter at @maddykennard