Queensland’s newest cyclone remains in its adolescence, still not yet fully formed and swirling off the coast as a tropical low.
It is expected to bring significant rainfall totals to parts of Queensland.
The Bureau of Meteorology (BOM) expects the system to develop into Tropical Cyclone Kirrily sometime on Wednesday.
For now, it has slowed its march towards the mainland, stalling slightly in the northern Coral Sea.
It’s currently forecast to hit the coast late on Thursday night and into Friday morning.
In the days following, it is expected to revert to a tropical low, dumping heavy rain.
With so many catchments across the state already saturated, there is a risk of flash flooding.
Dr Annie Lau from the University of Queensland’s School of Environment said the term tropical low — or tropical depression in the US — refers to a low-pressure system similar to a tropical cyclone, but of lower intensity.
“A tropical depression has to get low pressure to form — a lot of humidity in the atmosphere and also high temperatures,” Dr Lau said.
“We call it a moderate strength, low-pressure system. It’s often associated with monsoon troughs and is something that we see a lot in the tropics.
“Not every depression will develop into a cyclone. The atmospheric conditions have to be really favourable.”
BOM senior forecaster Felim Hanniffy said a tropical low is upgraded when its winds reach a certain speed.
“Once a system has wind speeds of more than gale force — that’s winds in excess of 65 kilometres an hour — and is more than halfway around the system’s low-pressure centre, then it becomes a named system.”
He said tropical lows needed very warm sea temperatures to form, along with lots of moisture in the air.
“Sea temperatures above 26.5 degrees are usually considered the threshold to sustain these systems, as they derive all their energy from that interaction.”
