Australian tropical cyclone season outlook

Pacific outlook

2015–16 Australian tropical cyclone season outlook

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.

The Australian tropical cyclone season runs from 1 November to 30  April. On average, there are around eleven tropical cyclones each season, four of which cross the coast. However, tropical cyclones can still significantly impact coastal communities even when cyclones remain well offshore.

While El Niño shifts the odds towards both fewer cyclones and a later first cyclone coastal crossing of the season, it does not guarantee this will always occur. For instance, during the strong El Niño 1997–98, tropical cyclone Sid formed in late December near Darwin before moving into the Gulf of Carpentaria and weakening. The remnant low produced record, devastating floods two weeks later over northern Queensland.

*Long-term average number of tropical cyclones, calculated using data from 1969–2014, may change slightly from one year to the next as a new season of data becomes available.

Outlook by region

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.

Interpreting the outlook

Percentages such as a 10% chance of having more tropical cyclones than average (90% chance of having fewer) mean that for every ten years with similar climate patterns to those currently observed, one year would be expected to have an above-average number of tropical cyclones and nine years would be expected to have a below-average number of tropical cyclones.

On average, eleven tropical cyclones occur over the full Australian region each season, with four making landfall. Although there are often fewer tropical cyclones on average over the Australian region during El Niño years, there has never been an El Niño year without at least one tropical cyclone making landfall on the Australian coast. As always, it is essential that all stakeholders and local communities prepare for the cyclone season.

Past Australian tropical cyclone season outlooks

Cyclone impacts

Before a tropical cyclone forms it is difficult to predict its exact strength and path, including whether it will make landfall. Along the east and west coasts fewer than half of the cyclones impact onshore areas, with the majority staying out to sea. Conversely, along the north coast more than half of the cyclones impact the coast. Tropical cyclones which remain out to sea can still cause storm surges, gales and areas of heavy/flooding rainfall over land.

Even after a tropical cyclone has passed, or has decayed below tropical cyclone strength, significant flooding may occur. The impacts of flooding may be more widespread than the area impacted by the cyclones damaging winds. The Bureau's flood warning services are an integral part of the response to tropical cyclones.

During the cyclone season, ensure you are well informed of any warnings from the Bureau of Meteorology and instructions from local Emergency Services authorities.

Diagram of storm tide height

Emergency services agencies

About the outlooks

This outlook is produced using statistical relationships between tropical cyclone numbers and two indicators: the Southern Oscillation Index (SOI) and the Niño3.4 sea surface temperature index (NINO3.4 SST). These indicators provide a measure of the strength of the atmospheric and oceanic state of the El Niño-Southern Oscillation (ENSO), respectively.

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

2015 July August September
SOI -14.7 -19.8 -17.7
NINO3.4 SST 1.60 °C 2.07 °C 2.28 °C

The current status of ENSO can be viewed via the Bureau's ENSO Wrap-up. During July–September 2015 the eastern tropical Pacific Ocean was much warmer than average, clearly exceeding El Niño thresholds. The Southern Oscillation Index, a measure of the atmospheric component of ENSO, has also been strongly negative through this period, indicating a significant El Niño event. Climate models suggest the 2015 El Niño will remain strong into early summer, and persist into early 2016.

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 various sub-regions this relationship, and thus forecast skill, can vary. Some regions have much higher forecast skill than others. The Northwestern sub-region has moderate skill, while the Western and Eastern regions both have low skill and the Northern region has very low skill.

Further information


Climate

Service notice

Network problems on 8 January disrupted processing of observations, affecting some climate information. Missing data are being retrieved and will be processed into our systems over coming weeks.