Sydney, Melbourne, Brisbane weather: Aussies to battle blistering heatwave and thunderstorm as warning issued

Aussies have been told to brace for two major weather events this week - a sweltering heatwave and a thunderstorm that could prove fatal for asthmatics .

An extremely hot air mass is causing temperatures to soar across Australia with extreme fire danger anticipated in southwest Queensland and northwest Victoria .

The multi-day heatwave is gripping parts of Queensland, New South Wales, the Northern Territory and Western Australia this week.

Temperatures were expected to reach a blistering 44C in parts of five states on Wednesday - NSW , QLD , SA, WA and the NT.

By 9.40am on Wednesday, temperatures had exceeded 40C in parts of southwest Queensland with the mercury hitting 42.5C at Birdsville on Tuesday.

'The hot weather will elevate fire danger ratings in some parts of the country, with extreme fire danger ratings predicted in Queensland's Channel Country and the Mallee in Victoria,' Weatherzone's Ben Domensino said.

'Fire authorities and emergency services in several states are closely watching a number of fires that were already burning as the sun rose on Wednesday.'

Residents from Dirranbandi in southwest Queensland were evacuated from their homes as firefighters battled a towering fire heading towards the town.

Residents with asthma in Melbourne and regional Victoria have been warned of a moderate risk of an epidemic thunderstorm asthma event on Wednesday.

The warning extends across Central, North Central, North East, South West, Wimmera, South and West Gippsland regions, as well as Melbourne.

The epidemic thunderstorm asthma forecast runs during the Victorian grass pollen season from October 1 to December 31 each year.

Thunderstorm asthma events can prove fatal with 10 Victorians losing their lives in a catastrophic event in 2016.

Those who suffer from hay fever or asthma are warned to be extra cautious during high pollen days, as the mixture of pollen, strong winds and rain can trigger severe asthma symptoms.

Shortly before a thunderstorm, tiny pollen grains can become swept up in gusts of wind, burst, and get caught in a person's lungs and cause breathing difficulties.

Even those without asthma or hay fever may experience breathing issues, including wheezing, chest tightness, coughing and shortness of breath.

Min 18 Max 27 Partly cloudy. Chance of any rain: 20 per cent.

Sydney area: Partly cloudy. Slight chance of a shower. Light winds becoming northeasterly 15 to 25km/h in the middle of the day then becoming light in the late evening.

Sun protection recommended from 8.50am to 4.20pm, UV Index predicted to reach 9 (very high).

Min 20 Max 32 Shower or two. Possible rainfall: 0 to 6mm. Chance of any rain: 70 per cent.

Sydney area: Partly cloudy. High chance of showers, most likely in the afternoon and evening. The chance of a thunderstorm. Winds northerly 15 to 20km/h shifting southerly 20 to 30km/h during the afternoon then becoming light during the evening.

Min 18 Max 31 Sunny. Chance of rain: 10 per cent.

Sydney area Sunny. Light winds becoming westerly 20 to 30 km/h during the morning then turning south to southwesterly during the evening.

Sun protection recommended from 8:40 am to 4:30 pm, UV Index predicted to reach 10 (very high).

Min 19 Max 33 Possible shower. Possible rainfall: 0 to 1mm. Chance of any rain: 40 per cent.

Melbourne area: Partly cloudy. Medium chance of showers, most likely in the late afternoon and evening. The chance of a thunderstorm. Winds northerly 35 to 50km/h shifting south to southwesterly 20 to 30km/h in the late afternoon.

Sun protection recommended from 9.20am to 4.50pm, UV Index predicted to reach 9 (very high).

Min 14 Max 22 Possible shower. Possible rainfall: 0 to 1mm. Chance of any rain: 40 per cent.

Melbourne area: Cloudy. Medium chance of showers. Winds south to southwesterly 15 to 25km/h becoming light during the evening.

Sun protection recommended from 9.10am to 4.40pm, UV Index predicted to reach 9 (very high).

Min 13 Max 20 Partly cloudy.

Melbourne area: Partly cloudy. Medium chance of showers in the morning and afternoon. Winds north-westerly 20 to 30 km/h turning west to south-westerly 25 to 35 km/h during the day.

Sun protection recommended from 9.20 am to 4.50 pm, UV Index predicted to reach 9 (very high).

Min 21 Max 31. Sunny. Chance of any rain: 5 per cent.

Brisbane area: Mostly sunny. The chance of a thunderstorm in the west in the morning and afternoon. Light winds becoming northerly 15 to 20km/h in the morning then tending northeasterly 20 to 3 km/h in the middle of the day.

Sun protection recommended from 7.40am to 3.20 pm, UV Index predicted to reach 10 (very high).

Min 21 Max 32 Sunny. Chance of any rain: 10 per cent.

Brisbane area: Sunny day. The chance of a thunderstorm in the west in the afternoon and evening. Light winds becoming north to northeasterly 20 to 30km/h during the morning.

Sun protection recommended from 7.30am to 3.20pm, UV Index predicted to reach 11 (extreme).

Min 23 Max 35 Shower or two.

Brisbane area Partly cloudy. Medium chance of showers, most likely in the morning and afternoon. The chance of a thunderstorm. Winds northerly 15 to 20 km/h increasing to 25 km/h before shifting east to southeasterly 15 to 20 km/h during the evening.

Sun protection recommended from 7.40 am to 3.20 pm, UV Index predicted to reach 10 (very high).

Min 18 Max 25 Partly cloudy. Possible rainfall: 0 to 1mm. Chance of any rain: 30 per cent.

Adelaide area: Partly cloudy. Slight chance of a shower, most likely in the morning. The chance of a thunderstorm. Winds north to northwesterly 20 to 30km/h shifting southwesterly 15 to 25km/h in the late morning.

Sun protection recommended from 9am to 4.50pm, UV Index predicted to reach 10 (very high).

Min 13 Max 22 Shower or two. Possible rainfall: 0 to 2mm. Chance of any rain: 60 per cent.

Adelaide area: Medium chance of showers, most likely in the morning. Mostly sunny afternoon. Light winds becoming westerly 25 to 35km/h during the morning.

Sun protection recommended from 9am to 4:50pm, UV Index predicted to reach 9 (very high).

Min 13 Max 21 Morning shower or two.

Adelaide area Medium chance of showers in the morning. Sunny afternoon. Winds westerly 25 to 35 km/h tending southwesterly 20 to 30 km/h during the morning then becoming light during the evening.

Sun protection recommended from 9.10am to 4.50pm, UV Index predicted to reach 9 (very high).

Min 13 Max 21 Cloudy. Chance of any rain: 20 per cent.

Perth area: Cloudy. Slight chance of a shower in the morning and early afternoon. Winds southwesterly 20 to 30km/h becoming light in the evening.

Sun protection recommended from 8.10am to 3.50pm, UV Index predicted to reach 10 (very high).

Min 9 Max 23 Mostly sunny. Chance of any rain: 10 per cent.

Perth area: Mostly sunny. Light winds becoming south to southwesterly 20 to 30km/h during the day then becoming light during the evening.

Sun protection recommended from 8.10am to 3.50pm, UV Index predicted to reach 10 (very high).

Min 12 Max 25 Partly cloudy.

Perth area Partly cloudy. Light winds becoming south to southwesterly 15 to 25 km/h in the morning.

Sun protection recommended from 8.10am to 3.50pm, UV Index predicted to reach 10 (very high).

Min 10 Max 32 Partly cloudy. Chance of any rain: 10 per cent.

Canberra area: The chance of fog in the early morning. Mostly sunny afternoon. Light winds becoming west to northwesterly 15 to 25km/h in the middle of the day then tending north to northwesterly 15 to 20 m/h in the evening.

Sun protection recommended from 8.50am to 4.40pm, UV Index predicted to reach 10 (very high).

Min 16 Max 29 Showers. Possible rainfall: 1 to 10mm. Chance of any rain: 80 per cent.

Canberra area: Cloudy. High chance of showers. The chance of a thunderstorm. Light winds becoming west to northwesterly 15 to 25km/h during the day then becoming light during the evening.

Sun protection recommended from 8.50am to 4.40pm, UV Index predicted to reach 10 (very high).

Min 9 Max 24 Sunny.

Canberra area Sunny. Winds northwesterly 25 to 35 km/h tending westerly 25 to 40 km/h during the day then becoming light during the evening.

Sun protection recommended from 8.50am to 4.40pm, UV Index predicted to reach 10 (very high).

Min 26 Max 35 Mostly sunny. Chance of any rain: 20 per cent.

Darwin City and Outer Darwin area: Mostly sunny. Slight chance of a shower. The chance of a thunderstorm. Light winds becoming north to northeasterly 15 to 20km/h in the middle of the day then becoming light in the late afternoon.

Sun protection recommended from 8.40am to 4.20pm, UV Index predicted to reach 13 (extreme).

Min 27 Max 34 Partly cloudy. Possible rainfall: 0 to 1mm. Chance of any rain: 30 per cent.

Darwin City and Outer Darwin area: Partly cloudy. Slight chance of a shower. The chance of a thunderstorm. Light winds.

Sun protection recommended from 8.30am to 4.20pm, UV Index predicted to reach 13 (extreme).

Min 27 Max 35 Partly cloudy. Shower or two. Chance of rain is 50 per cent.

Darwin City and Outer Darwin area Partly cloudy. Medium chance of showers, most likely in the morning. The chance of a thunderstorm.

Light winds becoming northwest to northeasterly 15 to 20 km/h during the day then becoming light during the evening.

Sun protection recommended from 8.30am to 4.20pm, UV Index predicted to reach 13 (extreme).

Min 9 Max 19 Possible afternoon shower. Possible rainfall: 0 to 1mm. Chance of any rain: 40 per cent.

Hobart area: Mostly sunny morning. Medium chance of showers, most likely in the afternoon and evening. Light winds becoming westerly 15 to 25km/h during the morning then shifting northeasterly 15 to 20km/h during the evening.

Sun protection recommended from 9.20am to 4.20pm, UV Index predicted to reach 7 (high).

Min 10 Max 28. Possible afternoon shower. Possible rainfall: 0 to 1mm. Chance of any rain: 40 per cent.

Hobart area: Mostly sunny morning. Medium chance of showers, most likely in the afternoon and early evening. Winds north to northwesterly 25 to 35km/h turning west to southwesterly 20 to 30km/h in the late afternoon.

Sun protection recommended from 9.10am to 4.30pm, UV Index predicted to reach 8 (very high).

Min 10 Max 17. Shower or two. Becoming windy. Chance of rain is 60 per cent.

Hobart area Sunny morning. Medium chance of showers, most likely in the afternoon and evening. Winds west to northwesterly 15 to 20 km/h tending east to south-easterly in the late afternoon then tending north-easterly in the late evening.

Sun protection recommended from 9.20am to 4.30pm, UV Index predicted to reach 7 (high).