Ever heard of a Rossby wave? Unless you're a weather buff, chances are slim.
But the term is about to become a lot more relevant to northern parts of Western Australia this weekend, with a tropical low set to develop into Tropical Cyclone Kelvin.
Experts predict the low will move parallel to the mainland throughout the day and early on Saturday, intensifying into a category two tropical cyclone.
It is then expected to take a southerly track and make landfall along the Kimberley/east Pilbara coast as a category three system.
What is a Rossby wave?
One of the factors influencing the strength of this system is the Rossby wave.
Also known as planetary waves, Rossby waves are naturally occurring in rotating fluids — in this case, the earth's atmosphere — and they form along the equator, moving from east to west, as a result of the rotation of the planet and the earth's geography.
They act in the transfer of heat from the tropics toward the poles and send cold air to the tropics.
Rossby waves can usually be observed as a pair of twin low pressure systems, with one on either side of the equator.
The Bureau of Meteorology's (BOM) Daniel Hayes said there was currently a cross-equatorial wind flow from the South China Sea feeding into a developing monsoon trough.
This trough is being pushed along by the Rossby wave, and is twinned with the developing low over northern WA.
"At the moment there's tropical storm Samba up near the Philippines and it's the twin with the low we've got developing down here," Mr Hayes said.
How does a wave become a cyclone?
Mr Hayes said a Rossby wave had given the developing low off WA's north a kind of atmospheric "shove".
"The effect of it can be to impart rotation into our monsoon troughs," Mr Hayes said.
"[The Rossby has] given this little system a bit of a shove and it might get going a bit stronger than maybe it would have without the Rossby wave influence."
He said the Rossby wave might not be only reason for a cyclone, but if the phenomenon is present, it can give the system the chance to pick up pace.
"So the existence of a Rossby wave can enhance whatever's going on," he said.
With Tropical Cyclone Kelvin set to develop over the weekend, authorities are urging people in the Kimberley to be prepared.
Already saturated soils and damaged roads means any extra rain to the region will likely wreak havoc.
The Bureau is forecasting isolated rainfall totals of up to 400 millimetres, with some parts of the region already receiving heavy falls in excess of 100mm.
