Australian tropical cyclone season outlook
See also:Pacific outlook Tropical cyclone warnings
About the outlooks
This outlook uses the statistical relationships between tropical cyclone numbers and two indicators: the Southern Oscillation Index (SOI) and the Niño3.4 sea surface temperature anomaly. 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 values were used in making the tropical cyclone season outlook.
Interpreting the outlook
Percentages such as a 60% chance of having more tropical cyclones than average (or a 40% chance of having fewer) mean that for every ten years with similar climate patterns to those currently observed, six years would be expected to have an above-average number of tropical cyclones and four years would be expected to have a below-average number.
The long-term average number of tropical cyclones per season in the Australian region (since 1969–70) is eleven, with four typically making landfall. Since the year 2000, there have been an average of nine tropical cyclones in the Australian region each season.
During El Niño events, there are typically less tropical cyclones than average, while more tend to occur during La Niña events. As always, it is essential that all local communities prepare for the cyclone season regardless of the outlook.
Australian region outlook accuracy
Over the entire Australian Region, this statistical relationship has proven to be highly accurate, or a skilful way to forecast tropical cyclone activity. However, across the sub-regions this relationship, and thus forecast skill, can vary. Some regions have much higher forecast skill than others. The Northwestern sub-region has good skill, while the Western and Eastern regions both have low skill and the Northern region has very low skill.
Australian tropical cyclone outlook region bounds
|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|
- Tropical Climate Update
- Southern Oscillation Index (SOI)
- Niño3.4 sea surface temperature index (NINO3.4 SST)
- Tropical cyclone climatology maps
Model: Kuleshov, Y., L. Qi, R. Fawcett and D. Jones, 2008: Improving preparedness to natural hazards: Tropical cyclone prediction for the Southern Hemisphere, in Advances in Geosciences, 12 Ocean Science, (Ed. Gan, J.), World Scientific Publishing, Singapore, 127-143.
Data: Kuleshov, Y., R. Fawcett, L. Qi, B. Trewin, D. Jones, J. McBride and H. Ramsay, 2010: Trends in tropical cyclones in the South Indian Ocean and the South Pacific Ocean, Journal of Geophysical Research 115, D01101, doi:10.1029/2009JD012372.
Average to slightly above average number of tropical cyclones likely for Australia in 2021–22
- An average to slightly-above-average number of tropical cyclones are expected for the 2021–22 Australian tropical cyclone season (November–April).
- On average, there are 9 to 11 tropical cyclones each season in the Australian region, four of which typically cross the coast.
- The increased likelihood of La Niña development in the tropical Pacific Ocean and average to warmer-than-average sea surface temperatures to the north of Australia have influenced this year's tropical cyclone outlook.
- In La Niña years, the first cyclone to make landfall on the Australian coast typically occurs earlier than normal, around the middle of December. During average years, the date of the first tropical cyclone to make landfall over Australia is typically in early January.
- Even if La Niña doesn't develop, some La Niña-like effects can still occur as tropical Pacific climate indicators approach La Niña thresholds.
- At least one tropical cyclone has crossed the Australian coast each 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 that form during La Niña years is typically greater than the number which form during non-La Niña years.
This outlook is based on the status of the El Niño–Southern Oscillation (ENSO) over the preceding July to September. ENSO has been in a neutral state since March 2021, with sea surface temperatures across the tropical Pacific Ocean cooling over the past two to three months. Climate models continue this cooling trend over the coming months, with three of seven models surveyed by the Bureau meeting La Niña criteria, while another two models briefly touch La Niña thresholds. The recent cooling combined with model outlooks mean a La Niña WATCH is currently in place. In the past when La Niña WATCH has been reached, a La Niña event has subsequently developed around 50% of the time.
Ocean temperatures are currently average to warmer than average surrounding northern parts of the country. Climate models predict waters to the north of Australia are likely to be warmer than average in the coming 3 months, marginally increasing the likelihood of tropical cyclones developing.
Tropical cyclone activity in the Australian region has large variability from year to year, due to the influence of naturally occurring climate drivers, such as ENSO. The number of tropical cyclones in the Australian region is generally higher with La Niña. In recent decades, the annual number of tropical cyclones that form in the Australian Region has decreased, from an average of 11 in the 50 years since 1970 to 9 since 2000.
Outlook by regionThe outlook indicates that an average to slightly-above-average number of tropical cyclones is most likely in the Australian region and all sub-regions for 2020–21.
- The Australian region has a 65% chance of having more tropical cyclones than average. This also means a 35% chance of fewer tropical cyclones than average. Typically, around 9 to 11 tropical cyclones form or pass through the Australian region in a season, with around four of these crossing the Australian coast in a season. Outlook accuracy for the Australian region is high.
- The Western region is forecast to experience an average number of tropical cyclones this season, with the likelihood of more than average at 61%. The chance of fewer than average is 39%. Typically, about 15% to 40% of tropical cyclones in the Western region create coastal impacts. The average number of tropical cyclones to form in or pass through the Western region is seven each season. Outlook accuracy for the Western region is low.
- The Northwestern sub-region has a 62% chance of more tropical cyclones than average and a 38% chance of fewer tropical cyclones than average. Typically, five cyclones form in or pass through this area each season. Around 40% of tropical cyclones, or their associated tropical lows, affect coastal areas of the Northwestern sub-region. Outlook accuracy for this region is moderate.
- The Northern region outlook suggests a near-average number of tropical cyclones with a 57% chance of more tropical cyclones than average and a 43% chance of fewer tropical cyclones than average. Typically, the Northern region experiences between 2 and 3 cyclones. About three-quarters of the tropical cyclones in the Northern region impact coastal regions. Outlook accuracy for this region is very low.
- The Eastern region outlook has a 66% chance of more tropical cyclones than average, with a 34% chance of fewer tropical cyclones than average. The average number of tropical cyclones for this region is four, and about a quarter of tropical cyclones in the Eastern region make landfall. Outlook accuracy for this region is low.
Product code: IDCKAUTCSO
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