Australia Weather News

Inland oceans created by weeks of record rain across Western Australia's Kimberley may have helped maintain or even intensify Tropical Cyclone Kelvin as it crossed over the region, the Bureau of Meteorology (BOM) has said.

Kelvin moved inland as the state's north was in recovery mode, following weeks of record rain from Tropical Cyclone Joyce in January and then a huge storm three weeks later that flooded an area larger than the state of Victoria.

The cyclone left the Great Northern Highway — the only supply road into Broome — cut off by what resembled an inland sea.

The bureau's Neil Bennett said Kelvin, which reached a category-two system, was able to develop mainly because of good moisture levels higher in the Earth's atmosphere, as well as the lack of strong winds.

But he said the effects of the water over land could not be ruled out.

"One of the other things that a cyclone needs is warm ocean water that's 26 degrees or higher, and the water that was on the land could have also been around that temperature," he said

"There is discussion around something called a brown ocean, where you have saturated soils that are warm, and as the cyclone moves over, there is this mimic effect of an ocean surface that it's passing over."

Mr Bennett said in the case of Cyclone Kelvin, it was likely the huge amounts of water over land slowed the weakening process of the system.

"The very wet area that it's moving into would have had some impact on that, and certainly looking at the rainfall figures through January for that Kimberley area coastal fringe part, they are very, very wet conditions," he said.

"What has happened in Broome over the last couple of months has just been extraordinary, and to be at this point as early as February is quite staggering."

The phenomenon of inland seas influencing the course of a storm played out last year when Hurricane Harvey hit Texas and Louisiana and became the wettest tropical cyclone on record in the US.

The system developed rapidly in the Gulf of Mexico, where it had all the right ingredients — an area of low pressure combined with warmer-than-average waters and favourable atmospheric conditions.

But, with Harvey stalled by high pressure systems on either side, the storm parked in one place, with floodwaters in those areas acting as an extension of the Gulf, meaning the system was practically feeding itself.

The landphoon phenomenon

Mr Bennett said moisture-laden soils in the desert could also help bring about storm systems that could not be classed as cyclones, but packed a similar punch.

He said these systems were known as landphoons.

"Landphoons can have the rotation of a cyclone, typhoon or hurricane, but are missing the eye and the wind strengths, and form over land," he said.

Mr Bennett said northern WA experienced a couple of these systems last year, and a large storm this year could also be classed as a landphoon.

'The tropical low we had in January that was very close to Broome was looking like a cyclone, but didn't have the wind speeds," he said.

"The wet season has the capacity to produce these very, very intense bursts of weather, and you don't have to have a tropical cyclone to find yourselves in a situation where communities are cut off because of flooding or you've got damage from strong winds."