Less than normal number of tropical cyclones expected for the 2015-16 season, Australia

less-than-normal-number-of-tropical-cyclones-expected-for-the-2015-16-season-australia

The Australian Bureau of Meteorology (BOM) has released its 2015–16 tropical cyclone season outlook today, signaling the start of severe weather public awareness campaigns in northern Australia. This year's strong El Niño is very likely to dominate the coming season.

The long-term average number of tropical cyclones in Australia during the November to April cyclone season is eleven, four of which cross the coast. However, because of the effects of the strong El Niño in the tropical Pacific Ocean this year, BOM expects fewer tropical cyclones than normal.

But, 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.

In January 2013, Oswald caused major flooding for virtually the entire Queensland coast as it tracked steadily south as an ex-tropical cyclone, or tropical low.

Despite expecting fewer cyclones this season, the Bureau is urging Australians in the tropics to start their cyclone season preparations now. Even tropical cyclones well offshore can have significant impacts on coastal areas. High winds, storm surges and large waves can create dangerous conditions.

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.

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.

Source: BOM

Featured image: Tropical Cyclone "Oswald" on January 21, 2015. Image credit: NASA Aqua/MODIS.

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