Welcome to the Bureau of Meteorology's Severe Weather Outlook for October 2020 to April 2021.
While severe weather can occur at any time of the year, this is the peak period for bushfires,
heatwaves, flooding, tropical cyclones, and severe thunderstorms.
This year our focus is on La Niña, which is likely to bring more rain to eastern
and northern Australia. In the months ahead Australia can expect:
an increased risk of widespread flooding for eastern Australia;
average to slightly above-average number of tropical cyclones;
normal bushfire potential in most States;
normal risk of heatwaves; and a and a typical risk of severe thunderstorms.
Above-average rains at times across eastern Australia have eased rainfall
deficiencies in some drought-affected areas. However, in Western Australia below-average
rains since April have increased the area affected by drought in the southern half of the State.
In late September the Bureau declared a La Niña event in the Pacific Ocean.
La Niña years typically bring our wettest spring and summers.
So, let's take a closer look at what this could mean for the severe weather season.
Localised major flooding can occur in any northern wet season but this season there is an increased
risk of widespread and prolonged riverine flooding across eastern and northern Australia.
Slow-moving tropical lows can cause widespread rainfall and inundation,
even in areas that have been previously dry.
The Australian region sees around eleven tropical cyclones on average each year,
with four of those crossing the coast. In recent decades we have seen a decline
in the overall number of tropical cyclones, which is consistent with
the expected impacts of climate change. However, this year we are expecting average
to above-average numbers of tropical cyclones and tropical lows, due to the influence of La Niña.
While we can't predict at the start of the season the size, intensity or exact location
where any one system may form, we do know that in every season, Australia has had at least one
tropical cyclone cross the coast, and cyclones can develop at any time throughout this period.
This means that communities right across northern Australia
need to stay prepared and informed throughout the tropical cyclone season.
2020 to 2021 fire season will be driven by vastly different climate
drivers than those of the last two years. With wetter-than-average conditions expected in
eastern and northern Australia, long-running large bushfires are less likely than in recent years.
However, a wetter spring can lead to increased grass growth, which could
increase fire danger as it dries during summer. If dry conditions continue in southwest Western
Australia as forecast, the potential for more fire weather days may increase.
Remember, bushfires occur every summer in southern Australia, and even short periods of hot and windy
weather will raise the fire risk, so communities need to have their bushfire plans ready.
Summer also brings heatwaves, which are Australia's most deadly severe weather.
Warm nights, after hot days, give our bodies little chance to cool down,
and heat stress becomes a significant risk to human health.
Heatwaves can also have an impact on our economy, with agriculture,
energy management, infrastructure and many other industries all affected.
Australia is warming and extreme heat days are more likely than compared
to the past due to the impacts of climate change. This summer, rain and increased humidity thanks
to La Niña means we face a reduced number of extreme heat days compared to recent years.
But while heatwaves may not be as severe in southern areas
they may last longer and be more humid, both of which can increase the risk to human health.
Severe thunderstorms can cause dangerous conditions including flash flooding,
large hail, damaging winds and even tornadoes. They are more common during the warmer months,
particularly in northern New South Wales, southern Queensland, inland
Western Australia, and across the tropical north. For southern Australia, the risk of heavy rain
with severe thunderstorms increases when there is a link to a tropical system; with more humid,
tropical air extending further south. Thunderstorm asthma can also be triggered by
storms with strong winds, especially from October to December when pollen levels are highest.
It is important to understand your weather and know your risk,
so that you are ready to act and stay safe. Be sure to follow advice from your
local emergency services on what to do before, during and after severe weather.
You can stay up to date with the latest forecast and warnings on the Bureau's website or app,
and be sure to keep an eye out for our weather update videos throughout the coming months.