Fewer cyclones than normal expected this season, BOM says
Cyclone Hilda was one of a series of cyclones to make landfall on WA's coast last season.
Cyclone Liua formed near the Solomon Islands on September 27 and was downgraded just before entering Australian waters.
This was remarkable because the South Pacific's cyclone season, like ours, is nominally from November to April — that is a whole month-and-a-half early!
So is Liua and its early arrival a sign of things to come?
The outlook doesn't suggest so. A likely El Nino this year means the weather bureau is saying the chance of more tropical cyclones than normal is small.
"Indications are for a lower-than-average number of tropical cyclones, and we are less likely to have widespread flooding," said Bruce Gunn, the state manager of BOM Queensland.
But that doesn't mean we can be complacent.
"We are heading into what should be a warmer and dryer season ahead, which means a longer bushfire season, that's already upon us, an increased chance of heatwaves, continuing drought, unfortunately, and also an increased chance of coral bleaching," Mr Gunn said.
Australia has never had a season without at least one cyclone crossing the coast.
Mr Gunn reminded us that any cyclone that formed in the Coral Sea had a one-in-four chance of crossing the coast.
"It only takes one tropical cyclone to make a season, just like we saw with Tropical Cyclone Debbie."
What is a normal year?
According to the Bureau of Meteorology's website, the long-term average number of cyclones per season in the Australian region since 1969-70 is 11, with an average of four making landfall. But since 2000 there has only been an average of nine cyclones each season.
It is projected that in the future there will be fewer but more high-severity cyclones around the world due to human-induced climate change.
The cyclone season outlook is dependent upon the Southern Oscillation Index and Pacific Ocean sea surface temperatures, both of which are also measures of the El Nino Southern Oscillation.
This is because cyclone occurrences and El Nino are linked.
Typically in El Nino years, like this one is tipped to be, there are less cyclones than average because of cooler-than-average western Pacific Ocean temperature and descending stable air over Australia.
La Nina years tend to bring more cyclones.
Who is in the firing zone?
Cyclones typically impact the coastal regions of northern Australia, but as Cyclone Debbie demonstrated in 2017, when flooding impacted from northern Queensland into New South Wales, their effects can be felt much further south.
It is expected that cyclones will travel further away from the equator as the climate warms.
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