AceWeatherDesk – Heatwave could have final say on Cyclone Jasper’s track with northern tropical coast most likely target

Ace Press News From Cutting Room Floor: Published: Dec.07: 2023: BOM & ABC & CAIRNS POST WEATHER NEWS: TELEGRAM Ace Daily News Link https://t.me/+PuI36tlDsM7GpOJe

Tropical Cyclone Jasper’s future track is becoming clearer and the latest modelling data indicates the northern tropical coast is the most likely target.

Initial forecasts indicated the system may take a very unusual route to southern Queensland, or even north-east New South Wales, but the current severe heatwave over Australia’s interior will be the ultimate judge on where the cyclone makes landfall.

Essentially the longer the heatwave lingers the more likely Jasper will strike the far north Queensland coast, while a cool change for NSW early next week would have driven the system further south to central Queensland, or even stall the storm offshore.

So how does the air temperature over Australia influence the movement of a cyclone well off the east coast?

What controls a cyclone’s path?

You often hear cyclones are difficult to predict, but the truth is not all systems are created equal.

The movement of tropical low-pressure systems, like everything else floating in the atmosphere, is mostly dependent on the wind.

In the case of a cyclone, which generates its own wind, we are talking about the environmental flow outside the periphery of the system.

When the winds surrounding a tropical cyclone are strong, forecasting its movement is relatively straightforward – it will move quickly in a steady direction.

Severe Tropical Cyclone Yasi in 2011 is a classic example of a system which was easy to forecast and therefore had a slim cone of uncertainty.

Yasi was forecast more than 48 hours before landfall to strike the coast just south of Innisfail early on February 3 – exactly when and where landfall occurred.

Then you have the opposite situation when surrounding winds are light and variable, and forecasting becomes a nightmare – track maps for Cyclone Kimi in 2021 just 36 hours prior to arrival showed a potential target for landfall more than 400 kilometres long and eventually the system petered out offshore without ever striking the coast.

Jasper being steered towards the north Queensland coast

Back to the current pattern — the link between the seemingly unrelated weather events of the heatwave and cyclone exists because the system responsible for soaring temperatures this week will also control Jasper’s course across the Coral Sea.

The intense heat is due to what’s called an upper high – a high pressure system a few kilometres above the ground.

An upper high causes air to descend towards the surface, and it warms rapidly on descent at a rate of up to 9.8 degrees Celsius per 1,000 metres.

Therefore, the longer the upper high and heatwave last, the longer Jasper will continue moving west towards Queensland’s north coast.

So what could disrupt this path? For Jasper to stall or turn left down the Queensland coast the centre of the upper high needs to move east of Australia early next week.

This would not only ease the current heatwave but also set-up a northerly flow to carry Jasper south.

The latest modelling indicates the southern track scenario is now extremely unlikely, meaning both an extension of the heatwave for western Queensland and NSW well into next week, along with a cyclonic impact on the north Queensland coast.

It’s still too early to make precise forecasts on when and where landfall will take place, or at what strength, and it’s still possible Jasper will stall before reaching the mainland.

Below is a non-official model generated strike probability for next Wednesday which shows the most likely target has shifted north of Cairns: https://www.cairnspost.com.au/news/cairns/weather/cairns-to-be-place-of-cyclone-jaspers-coastal-crossing-latest-bureau-guidance-outlines/news-story/b8ba4d4c262f0a088dadf57e10d809fc

How unusual is a December cyclone for Queensland?

December cyclones on the Queensland east coast are very unusual – there have been only three since 1970:

• Category one Tasha in 2010
• Category two Joy in 1990
• Category three Althea in 1971

What makes this system even more intriguing is the presence of El Niño, which normally leads to a late onset of the cyclone season, along with the recent reduction in cyclone numbers due to climate change.

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