Cyclone Numbers May be Up This Season

The Bureau of Meteorology has issued its Tropical Cyclone Season Outlook for 2017-2018 season and says the outlook for the country is typical, with the potential for increased activity in some key areas.

The Bureau forecasts a typical number of tropical cyclones are likely to form in the Australian region this season which runs from November to April.

We normally see between 10 and 13 cyclones in Australian waters each season, with around four of these crossing the coast.

Australia has always seen at least one tropical cyclone cross the coast each season.

The current data shows the overall Australian region has a 56% chance of having more tropical cyclones than average, meaning there’s a 44% chance of having fewer tropical cyclones than average.

The outlook, forecasters say, is based on the status of the El Niño–Southern Oscillation (ENSO) over the preceding July to September and that outlook is influenced by ENSO being neutral to weak La Niña-like conditions in the tropical Pacific Ocean, and slightly warmer-than-average ocean temperatures to the north and east of Australia.

They say that sea surface temperatures in the tropical Pacific Ocean have cooled since July and are now below average.

The majority of climate models suggest ocean temperatures may cool to La Niña thresholds during summer, although they predict a weak, short-lived to La Niña, should one occur.

Outlook by Region

The outlook indicates that a typical number of tropical cyclones is most likely in the Australian region and all sub-regions for 2017–18.

• The Northern region outlook suggests an average number of tropical cyclones with a 53% chance of more tropical cyclones than average and a 47% chance of fewer tropical cyclones than average.

In a typical year the Northern region experiences around 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 coastal regions. The Bureau says their Outlook accuracy for this region is very low.

• The Eastern region outlook shows a near average season is most likely, with a 54% chance of more tropical cyclones than average and a 46% chance of fewer.

About a quarter of tropical cyclones in the Eastern region make landfall. Outlook accuracy, the Burau says, for this region is low.

• The Western region is likely to experience an average number of tropical cyclones this season, with the likelihood of more than average at 52%. The chance of fewer than average is 48%.

Typically, between about 15% and 40% of tropical cyclones in the Western region create coastal impacts. Outlook accuracy for the Western region is low.

• The Northwestern sub-region has a 56% chance of more tropical cyclones than average and a 44% 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, effect coastal areas of the Northwestern sub-region. Outlook accuracy for this region is moderate.

The Bureau reminds us that during ENSO-neutral years, the first tropical cyclone to make landfall over Australia typically occurs in late December. In La Niña years, the first cyclone landfall typically occurs earlier, around the first week of December.

And they say, we all need to remember that Tropical Cyclones that do not make landfall can still have a significant impact on coastal communities, through heavy rainfall, storm surges, and large waves.