The stubborn high-pressure system behind Australia’s record heatwaves



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Parts of Australia have broken multiple heat records over the past week.
Vicki/Flickr, CC BY-NC-SA

Steve Turton, CQUniversity Australia

If you think the weather this month has been like Groundhog Day (albeit much hotter), you’d probably be right! Much like a stuck record, weather systems seem to have stalled over most of the country.

Brisbane residents are questioning the lack of rain, storms and heat. Darwin has just endured its second-latest monsoon onset on record after weeks of heat and humidity. Interior towns and cities have experienced significantly hot weather with a number of new maximum and minimum temperature records broken, along with records for consecutive days over 35℃.




Read more:
Coastal seas around New Zealand are heading into a marine heatwave, again


Perth has largely escaped the heat so far this summer, while Sydney and Hobart have had a mixed bag. Coastal sea breezes have tempered conditions in the south and southeast of the continent. However, heatwaves are forecast for Melbourne and much of the southeast, with the arrival of strong, hot northerly winds. This will also bring extreme or severe fire weather conditions in many areas, including Tasmania. Adelaide, meanwhile, has sweltered through the hottest day on record for any Australian capital.


Bureau of Meteorology

These weather patterns across the country are largely due to a stubborn blocking high-pressure system that has remained over the Tasman Sea since early January, affecting weather on both sides of the ditch. This type of strong high-pressure system typically forms further south than usual, and remains almost stationary for an extended period, thus blocking the west-to-east progression of weather systems across southern Australia.




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Australia’s ‘deadliest natural hazard’: what’s your heatwave plan?


Sometimes, these blocking highs position themselves over the Great Australian Bight. They can occur at any time of year, and can stay in the Australian region from several days to several weeks.

This schematic shows a ‘blocking high’ preventing weather systems moving across Australia.
Understanding Climate Change in Australia report

Winds rotate anticlockwise around high-pressure systems in the Southern Hemisphere. On the northern flank of the blocking high, southeast trade winds have been affecting northern New South Wales and eastern Queensland due to a persistent ridge of high pressure. These winds have been largely cool and dry, with only the far north of Queensland experiencing significant showers. The ridge has kept the inland trough further west over inland NSW and Queensland, preventing normal afternoon thunderstorm activity in the inland, and adding to the woes of the extended drought.

Cool, moist weather from the Southern Ocean is being displaced southeast by the blocking high, resulting in prolonged continental heatwaves and lack of rain. On the western flank of the blocking high, hot dry northerly winds from the arid centre are pushing through South Australia and Victoria, generating heatwave conditions.




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Across the ditch, cooler and drier southerly winds are affecting much of New Zealand. Only the southwest of the South Island is getting any significant rain due to persistent moist westerlies on the southern flank of the blocking high.

An unusually strong ridge of high pressure across Queensland, extending up to Cape York, has kept the monsoon trough north of the continent. This pattern is forecast to change as a deep tropical depression forms in the Gulf of Carpentaria over the coming days and moves south into northern Queensland. Unfortunately, the stubborn ridge of high pressure over central Queensland is likely to block the rain-bearing low from moving much further south over drought-stricken parts of inland Queensland and NSW.




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While parts of the country have sweltered, the far southwest of Australia has experienced cooler and wetter than average conditions this month. Cape Leeuwin, Australia’s most southwesterly point, set a 123-year daily rainfall record for January, recording a massive 57mm of rainfall.


Bureau of Meteorology

In the short term, there is no indication that the blocking high will break down or move eastward. Forecasters on both sides of the Tasman expect the pattern to continue until February at least.




Read more:
Are heatwaves ‘worsening’ and have ‘hot days’ doubled in Australia in the last 50 years?


The Conversation


Steve Turton, Adjunct Professor of Environmental Geography, CQUniversity Australia

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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Australia: Victoria – Bushfire Crisis


With major bushfires burning around the country – Western Australia, South Australia, New South Wales and Victoria especially – conditions are expected to worsen before they get better. Australia is in the grip of a major heatwave with temperatures well into the forties and approaching the fifty degrees celsius mark in many areas. It has been this way for weeks in Outback Australia and is expected to continue for some time.

Australia: Catastrophic Bushfire Conditions Generate Massive Bushfire Across the South East


South-Eastern Australia is in the grip of a heatwave with temperatures threatening the record books. Temperatures across the country are reaching between 40 degrees Celsius (104 degrees Fahrenheit) and 50 degrees Celsius (122 degrees Fahrenheit), with the hottest recorded temperatures in many centres threatened, as well as the highest temperature every recorded in Australia.

For more on the fires visit:
Battlefront NSW: State on bushfire red alert | News.com.au.

AUSTRALIA: BUSHFIRES UPDATE – Sunday 15 February 2009


It has been over a week since the bushfires in Victoria took a turn for the worse. Bushfires had been burning in heatwave affected Victoria for some time previous to the conflagration that took place last Saturday, but it was on that day that they turned deadly.

A week since that deadly day and the death toll remains unclear, with 181 confirmed dead and some 120 people still missing, feared dead. Over 1800 homes have been destroyed, along with many other buildings including churches, schools, police stations and shops. The damage bill is expected to run into the billions of dollars.

Whatever way you look at it, this bushfire crisis is a major disaster and the worst to have ever come to Australia. All other disasters fade away in contrast to this.

The death toll breaks down to this:

Callignee Upper

1

Callignee

11

Koornalla

4

Hazelwood

4

Jeeralang

1

Mudgegonga

2

Eaglehawk

1

Humevale

6

Steels Creek

7

St Andrews

22

Arthurs Creek

3

Yarra Glen

1

Hazeldene

2

Taggerty

3

Marysville

15

Narbethong

9

Flowerdale

4

Heathcote Junction

1

Kinglake

35

Kinglake West

4

Strathewen

30

Wandong

4

Clonbinane

1

 

 

Others

10

 

 

Total

181

 

Thus far we know that some of the fires were started by lightening strikes and arsonists. It is now thought that at least one of the fires may have been started by poorly maintained electrical infrastructure near Kilmore East. A class action against the private contractor SP Ausnet (Singapore based) is being planned. Over 100 people died from a blaze in the Kilmore East area.

ABOVE: Another theft of a bushfire appeal collection tin

AUSTRALIA: BUSHFIRE CATASTROPHE


Over the last couple of weeks temperatures in south-eastern Australia have been steadily rising and finally reaching searing heatwave conditions in the last week or so. Temperatures have been between 40 and 48 degrees Celsius for almost 2 weeks in may inland areas of Victoria, South Australia and New South Wales. Finally the temperatures have peaked this weekend.

With the searing heat has now come strong hot winds and out of control bushfires. Many bushfires have become uncontrollable and unmanageable to any degree whatsoever and many are beginning to combine. These fires have become massive wildfires and are engulfing huge areas of inland south-eastern Australia.

The worst hit areas are to be found in Victoria where it is now confirmed that at least 65 people have died since Saturday – many more people are injured and missing and the death toll will climb. 700 homes and many other buildings including shops, police stations, service stations, hotels, motels, schools and many other buildings have been destroyed. Whole towns have been practically razed and wiped from the face of the earth.

This disaster is one of the worst bushfire catastrophes to have hit Australia, if not the worst ever. Certainly in the terms of loss of life this is by far the worst fires ever – and the disaster is ongoing, with many fires still burning.

Part 1:

Part 2:

ABOVE: An overview of the fires in Victoria

ABOVE: Bunyip State Forest Fire – photos from the start on Thursday through to Saturday

ABOVE: The Churchill fire in Victoria

ABOVE: Kevin Rudd activates the Commonwealth Disaster Plan

ABOVE: Various other reports