Bushfire weather and heatwaves in Australia

By Julia · weather-au.com editorial team · Published 16 October 2026

The four ingredients of a bad fire day

Dangerous fire weather is a recipe, not a temperature. It needs dry fuel after weeks without rain, low humidity, high temperature and, above all, strong wind. Take away the wind and a 42-degree day is merely uncomfortable; add 60 km/h gusts and the same day becomes unmanageable.

The worst days share a pattern: a hot north-westerly draws desert air towards the south-east, then a cool change arrives from the south-west in the afternoon. That wind shift turns the long flank of a fire into a new, much wider front, which is why it has caused the greatest loss of life in Australian fire history.

Humidity is the number worth watching alongside temperature. Below about 15 per cent, fine fuels ignite from a single ember; above 30 per cent, the same fire struggles. Our town pages show humidity next to the forecast for exactly this reason.

Reading the fire danger ratings

Since 2022 the whole country uses one system, the Australian Fire Danger Rating System, with four levels: Moderate, High, Extreme and Catastrophic. Below Moderate no rating is displayed, which means conditions do not warrant action rather than that nothing can burn.

The levels are advice about what to do, not a score. High means be ready to act; Extreme means leaving early is the safest option for those in bush areas; Catastrophic means that staying is not survivable in a well prepared house, and the advice is to be away before the day begins.

Ratings are issued per fire district by each state service, and total fire bans follow them. They are published the afternoon before, which is why the decision to cancel a hike or move a caravan is made the night before, not on the morning itself.

Where and when the season falls

Australia does not have one fire season but several. In the south — Victoria, Tasmania, South Australia, southern New South Wales and the south-west of Western Australia — the peak is December to March. In the subtropics around Brisbane it shifts to spring, and across the tropical north it is the dry season, from June to October, when the grass cures.

That is why the national picture can look contradictory: the Top End burns in August while Melbourne is cold and wet, and the Alps burn in January while Darwin is under monsoon rain.

Years matter as much as months. After a dry winter the fuel is ready early and the season starts in November; after a wet one, grass grows thick and the risk simply moves from forest to grassland.

Heatwaves: the coast and the inland

A heatwave is defined by three days of unusual heat for that place, not by a fixed number. Thirty-eight degrees is a heatwave in Hobart and an ordinary summer day in Alice Springs, and the health effects follow the local definition, because bodies adapt to their own climate.

The coast and the interior suffer differently. Inland heat is dry and nights cool off, which gives some relief; coastal heat in Sydney or Brisbane comes with humidity that keeps night minima above 25 degrees, and it is those warm nights that fill hospitals.

Two numbers decide how hard a heatwave will be: the overnight minimum and the number of consecutive days. Both are visible on our sixteen-day forecast, and they tell you more than the headline maximum, which is the figure everyone quotes.