Tropical Cyclones on the northwest Australian coast

The northwest Australian coastline between Broome and Exmouth is the most cyclone-prone region of Australia.  On average approximately five Tropical Cyclones occur during each cyclone season over the warm ocean waters off the northwest coast between 105°E and 125°E - with about two cyclones crossing the coast each season.  In fact, 75 % of severe cyclone crossings in Australia (1970 to 2008) have occurred on the northwest Australian coastline.

The Australian cyclone season officially runs from November to April, although very few have occurred in November (Figure 1).  At the start of the cyclone season, the most likely area to be affected by Tropical Cyclones is the Kimberley and Pilbara regions, with areas further south (including the Ningaloo Coast) more likely to be affected later in the season.  The chance of experiencing a category 4 or 5 cyclone is highest in March and April (Figure 1).

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Figure 1.  Monthy frequency of Tropical Cyclones off northwest Australia (1988 to 2004).  Data extracted from the Bureau of Meteorology.

While Tropical Cyclones can move in many different directions, off the northwest Australian coast they generally follow a much more predictable path than off the Queensland coast.  In the northwest, Tropical Cyclones usually initially head to the west-southwest at speeds of 5-20 km/h and then take a more southerly track as they move further to the south.  If they do move south of about 22°S or cross the Pilbara coast they tend to curve to the south-southeast and accelerate.  

What are Tropical Cyclones?

Tropical Cyclones are low pressure systems that form over warm tropical waters, have gale force winds (sustained winds of ≥ 63 km/h and gusts > 90 km/h) near the centre, and generally have a distinct life cycle of approximately 4 to 7 days.  Tropical Cyclones derive their energy from the warm tropical oceans and do not form unless the sea surface temperature is > 26.5°C - although once formed they can persist over lower sea surface temperatures.

The severity of a Tropical Cyclone is described in terms of categories ranging from 1 to 5 related to the zone of maximum winds (Table 1). 

Trends in cyclone activity in the Australian region (105°E to 160°E) show that the total number of Tropical Cyclones has decreased in recent decades, but the number of severe cyclones has increased during this time.

The Bureau of Meteorology’ Current Tropical Cyclones resource provides more information and current updates on Tropical Cyclones in Australia.

Tropical Cyclones on the Ningaloo Coast

Due to its location on the southern end of Australia’s most cyclone-prone region, the Ningaloo Coast has a history of cyclone events.  Tropical Cyclones that impact the Ningaloo Coast typically form over warm ocean waters to the north and steer to the southwest where they tend to take a more southerly track as they move further south.  Most notably, in March 1999 Tropical Cyclone Vance moved down the Exmouth Gulf causing winds recorded to 267 km/h (the highest ever wind gust measured on the Australian mainland). 

Along the Ningaloo Coast the cyclone season runs from mid-December to April, peaking in February and March (Figure 2).  Overall it is estimated that a cyclone impact causing wind gusts in excess of 90 km/h in the vicinity of Exmouth occurs about once every two to three years on average.  Given that cyclones generally weaken as they move southwards over cooler water and to latitudes where the atmospheric winds are unfavourable for cyclones, Carnarvon generally experiences less cyclones than the central and northern Ningaloo Coast. 

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Figure 2.  Monthy frequency of Tropical Cyclones on the Ningaloo Coast (1910 to 2004).  Data extracted from the Bureau of Meteorology.

Due to the active cyclone history of the Ningaloo Coast, there has been recorded damage to property – Table 2 provides a snap shot of the most notable Tropical Cyclones post-1963.  The development of the offshore oil and gas and the tourism industry along the Ningaloo Coast has increased the damage potential of Tropical Cyclones in the region – due to property damage, service disruptions, flooding, production shut downs, and disruptions to shipping activities.  Fortunately modern structures are built according to cyclone wind ratings and are less susceptible to damaging winds than earlier constructions. 

Tracks of past Tropical Cyclones along the Ningaloo and northwest Australian coasts can be accessed by the Bureau of Meteorology’s Interactive Tropical Cyclone Plotter.