Some Brisbane residents have a clean-up job ahead after an “unusual” dry microburst brought wind gusts of up to 80 kilometres per hour.
The storm swept through the Carina Heights area on Thursday afternoon, uprooting trees, damaging property and cutting power to 25,000 homes in south-east Queensland.
Bureau of Meteorology (BOM) forecaster Matthew Bass said “the conditions were quite unusual”.
“The winds we saw across Brisbane are a specific type of microburst called a dry microburst,” he said.
“What we had yesterday was quite a dry westerly air mass — basically, westerly [winds] don’t tend to happen at all in Brisbane in January.
“It’s quite unheard of.”
A storm in the Gympie region could have also been caused by a microburst, similar to what Brisbane experienced, the BOM said.
What is a microburst?
A microburst is a “downburst” on a smaller scale. A downburst is a concentrated downdraft — typically lasting five to 15 minutes — of unusually high speed.
According to the BOM, there are two types of microbursts — wet and dry.
Microbursts are a “sudden, localised column of sinking air or downdraft, that can produce winds of damaging force”, a spokesperson said.
Sometimes the damage caused by a microburst can be mistaken for a tornado.
A wet microburst can occur during thunderstorms and is accompanied by “significant precipitation at the surface”.
But Thursday’s storm in Brisbane’s south-east was considered a dry microburst, caused by wind gusts.
“What that means is you’re getting a whole lot of rainfall that comes out of a storm into a dry air mass beneath it,” Mr Bass said.
“That rain cools down the air [and] makes it heavier and gives it a bit more escalation as it comes down towards the ground, so it gives it a bit more of a punch when it comes down.”
Forecasters said hot temperatures of up to 37.4 degrees in Brisbane — the hottest January day since 2018 — helped facilitate the microburst.
How common are microbursts?
According to the BOM, microbursts occur right across the country and are one of the most destructive winds of any weather event, aside from cyclones.
Senior forecaster Dean Marramore said dry microbursts are actually “pretty common” in inland and outback areas across Australia due to “really hot conditions”.
But dry microbursts are less likely to occur in highly populated areas, he said.
“They do happen from time to time through eastern Australia if the conditions are right,” he said.
Highly populated areas are more likely to experience wet microbursts.
A study found short-duration extreme rainfall events have intensified over Sydney in the past 20 years.
How can you prepare for a microburst?
BOM’s Shane Kennedy said that Brisbane’s storm was particularly small, making it difficult for forecasters to see it would produce damaging wind gusts.
But he said there’s generally “telltale” signs of a microburst developing, including how much dry air is in the atmosphere.
When storms are forecast, the State Emergency Service advises residents to:
- Check your roof by removing leaves and debris from the drainage channels to prevent build-up and blockages.
- Clean your gutters, drains and downpipes and tidy up overgrown gardens that may cause damage during high winds.
- Learn how to safely turn off your electricity, water and gas to help prevent damage during potential flooding.
- Furniture and trampolines can become hazards during high winds and flooding — tie them down or bring items inside whenever possible.
