Australian tropical cyclone season long-range forecast

The tropical cyclone season runs from 1 November to 30 April

See also:

Pacific season 7 day tropical cyclone forecast


About the long-range forecasts

The tropical cyclone season long-range forecast uses the statistical relationships between historical tropical cyclone numbers and two indicators: the Southern Oscillation Index (SOI) and the Niño3.4 sea surface temperature (SST) anomaly (relative to the 1991–2020 average). These two indicators provide a measure of the atmospheric and oceanic state, respectively, of El Niño-Southern Oscillation (ENSO).

The July, August and September SOI and NINO3.4 anomaly values are used in making the Australian Tropical Cyclone Outlook.

Interpreting the long-range forecast

The statistical long-range forecast generates a percentage chance that the upcoming season will have more tropical cyclones than the long-term average. For example, a 40% chance of having more than average tropical cyclones means that for every ten years with similar ENSO patterns to those currently observed, four years would be expected to have an above average number. The percentage chance is converted into a categorical forecast whether each region is expected to have an above average, average, or below average number of tropical cyclones.

The long-term average, since 1969–70, number of tropical cyclones per season in the Australian region is 11, with 4 typically making landfall. In the South Pacific region, the long-term average is 9 tropical cyclones per season.

In recent decades, in a globally warmer climate, the total number of tropical cyclones that have formed in the Australian region has decreased, to an average of 9 per season since 2000–01. In a globally warmer climate, it is generally more difficult for tropical cyclones to form due to less favourable atmospheric conditions. However, due to increased energy provided by warmer oceans, tropical cyclones that do form are likely to be more intense and produce more rainfall.

During El Niño events, there are typically fewer tropical cyclones than average, while more tend to occur during La Niña events.

Australian region long-range forecast accuracy

Historically, over the entire Australian Region, this statistical relationship has had high accuracy, i.e. has skilfully predicted total tropical cyclone activity. However, across the sub-regions this relationship, and thus forecast skill, can vary. The North-western sub-region has moderate to high skill, the Western region has moderate skill, and Eastern and Northern regions both have low skill.

The statistical relationship between historical tropical cyclones numbers and climate indicators used by the long-range forecast does not explicitly include global warming.

Australian tropical cyclone long-range forecast region bounds
Region Top Bottom Left Right
Australian region 5° S 40° S 90° E 160° E
Western region 5° S 40° S 90° E 125° E
NW sub-region 5° S 25° S 105° E 130° E
Northern region 5° S 40° S 125° E 142.5° E
Eastern region 5° S 40° S 142.5° E 160° E

Archive

El Niño likely to decrease Australian cyclone numbers

  • A less active Australian tropical cyclone season (November–April) is expected for 2015–16.
  • This outlook is driven by a strong El Niño which typically reduces the number of cyclones observed in the Australian region.
  • During El Niño seasons, the average date of the first tropical cyclone to cross the coast (second week of January) is later than during neutral years.
  • El Niño typically reduces the number of coastal crossings, but at least one tropical cyclone has crossed the Australian coast each cyclone season since reliable records began in the 1970s.
  • Northern Australian coastal regions should still prepare for the cyclone season.

Regional details

The outlook indicates that fewer tropical cyclones than average are likely in all regions for the 2015–16 season.

  • The Australian region has only a 9% chance of having more tropical cyclones than average, meaning a 91% chance of having fewer tropical cyclones than average. Typically, around 4 tropical cyclones cross the Australian coastline in a season. Outlook accuracy for the Australian region is high.

  • The Western region is most likely to experience fewer tropical cyclones than average this season, with a 25% chance of more tropical cyclones than average (meaning a 75% chance of fewer tropical cyclones than average). Typically between about 15% and 40% of tropical cyclones in the Western region will have an impact upon the coast. Outlook accuracy for the Western region is low.

  • The Northwestern sub-region is most likely to experience fewer tropical cyclones than average this season, with a 15% chance of more tropical cyclones than average and an 85% chance of fewer tropical cyclones than average. Typically, five cyclones form in or pass through this area each season. Around 40% of tropical cyclones in the Northwestern sub-region impact on the coast at some stage in their life cycle. Outlook accuracy in this region is moderate.

  • The Northern region is most likely to experience fewer tropical cyclones than average this season, with a 36% chance of more tropical cyclones than average; 64% chance of fewer tropical cyclones than average. In an average year the Northern region typically experiences three cyclones, and one or two tropical lows that later become cyclones after moving into the Western or Eastern regions. About three-quarters of the tropical cyclones in the Northern region impact the coast. Outlook accuracy in this region is very low.

  • The Eastern region is most likely to experience fewer tropical cyclones than average this season, with only a 27% chance of more than average; 73% chance of fewer than average. About a quarter of tropical cyclones in the Eastern region make landfall. Outlook accuracy in this region is low.

 

Product code: IDCKAUTCSO

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