La Nina: Tropical cyclones could start earlier and be more frequent

The first cyclone to make landfall could be as early as mid-December, rather than the usual early January, Bureau of Meteorology forecasters say.

During the past 50 years there has been an average of 11 cyclones a year in Australia, four of which typically cross the coast.

"Tropical cyclone outlook predicts a 73 per cent chance of above-average cyclone activity this season," a BoM alert states.

"Current climate conditions favour the first tropical cyclone occurring early this season. They also favour the first tropical cyclone to cross the coast being earlier than average."

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Long-term annual averages show the western region usually has the highest number of tropical cyclones at seven. This is followed by the north-western sub-region (five), eastern region (four) and northern region (three).

For 2022-23, the outlook indicates that an above-average number of tropical cyclones is likely in all but the northern region.

This region has a 73 per cent chance of having more tropical cyclones than average. This is also equivalent to a 27 per cent chance of fewer tropical cyclones than average.

The BoM's outlook accuracy for the Australian region is high.

This region has a 69 per cent chance of having more tropical cyclones than average. Typically, at least one tropical cyclone in the Western region will create coastal impacts, regardless of how many make landfall.

The BoM's outlook accuracy for the western region is moderate.

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This region has a 70 per cent chance of more tropical cyclones than average. Around three tropical systems (tropical cyclones, or their associated tropical lows) are expected to affect coastal areas of the Northwestern sub-region.

The BoM's outlook accuracy for this region is moderate.

This region has a 61 per cent chance of more tropical cyclones than average. About three-quarters of the tropical cyclones in the northern region have some form of impact upon coastal regions.

The BoM's outlook accuracy for the region is low.

This region has a 74 per cent chance of more tropical cyclones than average. The average number of tropical cyclones for this region is four, and around one of these make landfall.

The BoM's outlook accuracy for this region is moderate.

The tropical cyclone season typically runs from November 1 to April 30, although tropical cyclones can and do form outside of these dates.

At least one tropical cyclone has crossed the Australian coastline in every season since reliable records began in the 1970s.

Cyclone formation is rarely spread evenly throughout the season; often quiet periods are followed by bursts of activity.

Tropical lows that do not intensify into cyclones, or lows that are the remnants of older cyclones, can still produce damaging winds, widespread rainfall, and dangerous flooding. These impacts can extend beyond the tropics into southern areas of the country.

Like tropical cyclones, the number of tropical lows during La Nina years is typically greater than the number which form during non-La Nina years.

From the 2005-06 season onwards, the typical number of tropical lows has been seven for all years, and 10 for La Nina years.