Residents of the Australian capital of Canberra are bracing for the most serious bush fire threat in 17 years amid a weekend of extreme heat and strong winds. A blaze burning south of the city is forecast to at least triple in size, lobbing “ember attacks” against the city’s southern suburbs and potentially burning through the small village of Tharwa.

The entire Australian Capital Territory (ACT), which includes the city of about 400,000, is under a state of emergency due to the Orroral Valley Fire burning in Namadgi National Park, about 30 miles south of the city. A heat wave from Friday through Sunday, along with shifting, gusty winds and low humidity, will make for severe fire conditions and allow the fire to spread far beyond its current footprint.

ACT Chief Minister Andrew Barr said during a Friday news conference that the city is now facing its greatest bush fire threat since the deadly firestorm of 2003, which also involved a fire that advanced on the city from the surrounding forests. That blaze killed four, injured more than 400 and destroyed about 500 homes.

“The combination of extreme heat, wind and a dry landscape will place suburbs in Canberra’s south at risk in the coming days,” Barr said. The fire has grown to about 8 percent of the total land mass of the ACT, Barr said, warning that it is set to expand significantly.

“This fire may become very unpredictable. It may become uncontrollable,” he said. He said the state of emergency would be in place “for as long as Canberra is at risk.”

This is the first time the ACT government has declared a state of emergency since the 2003 fires, Barr noted, saying it’s justified based on predictions of the fire’s spread in coming days.

“The state of emergency is the strongest signal we can send to the ACT community that they must prepare themselves and their families for the worst possible situation.”

The government has taken steps to prepare for the fires, including moving some water supplies from areas in the path of the fire to areas farther to the north, and transferring animals that were being cared for from previous fires to safer nature reserves elsewhere. Evacuation centers are now open, with more coming online as needed, Barr said.

Fire crews have been stationed at the outskirts of the city, including assets from the Australian Defense Force and what Barr described as “urban strike teams.” Flames are visible from the city itself.

The forecast high temperature in Canberra on Saturday is 106 degrees (41 degrees Celsius), with only slightly cooler conditions Sunday. A cold front approaching the region Sunday is projected to lose much of its moisture before arriving in the region, and instead of bringing beneficial rains it could set off dry thunderstorms that spark lightning and deliver little rain. Such storms could start new blazes.

The weather this weekend will be conducive to extreme fire behavior and rapid fire spread. This includes phenomena such as fire-generated thunderstorms, also known as pyrocumulonimbus clouds and ember attacks that can make firefighting next to impossible.

Such conditions have been seen repeatedly this fire season across the parched landscape of Australia, as an unprecedented spate of fires has consumed massive amounts of forests and grasslands, particularly in Victoria, New South Wales and Queensland. The fires have severely damaged or destroyed areas rich in biodiversity, imperiling species that are unique to Australia.

They have effectively doubled the country’s annual greenhouse gas emissions, sent smoke around the world and threatened the political fortunes of pro-coal Prime Minister Scott Morrison, who has downplayed climate change’s role in exacerbating the bush fire season.

Studies show that there has been an increase in heat waves and high-fire-risk days in southeastern Australia and that these trends are due in large part to human-caused global warming.

The country was never as hot and as dry at the same time as it was in 2019, which helped set the stage for the devastating fires. In December, Australia recorded its two hottest days on record. On Dec. 18, the nationally averaged maximum temperature was 107.4 degrees (41.9 Celsius), shattering the old record of 104.5 degrees (40.3 Celsius) set in 2013.

Australia has warmed by just over 1.8 degrees (1 degree Celsius) since 1910, with most of the warming occurring since 1950. The Bureau of Meteorology has found an uptick in the frequency of extreme heat events and severity of drought conditions during this period.

In addition, most of the country saw the highest-ever forest fire danger index — a key measure of potential fire severity — during December, when many of the deadliest and most damaging blazes occurred.