Tropical Cyclones Affecting Exmouth

Tracks | Flooding | Storm Surge | Notable TCs | TC Vance (pdf report)

Located on the western tip of the Pilbara coast, the most cyclone-prone part of Australia's coast, Exmouth has felt the full force of one of the strongest cyclones in Australia's history. In March 1999 tropical cyclone Vance moved down Exmouth Gulf causing winds recorded to 267 km/h, the highest ever wind gust measured on the Australian mainland (see TC Vance (pdf report)).

It is difficult to compare historical cyclones prior to Exmouth being developed in the 1960s. The pearling fleet from Port Hedland regularly visited Exmouth Gulf in the late 1800s and in December 1875 a cyclone devastated the fleet sinking several boats and claiming 59 lives. Pastoral stations and then the Cape Vlamingh lighthouse (1911) provided some details of cyclones during the early years. The first recorded major cyclone impact was in February 1945 when the three-year old naval base was extensively damaged and troops were withdrawn.

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. However, the frequency is not evenly distributed. Since 1982 there have only been three cyclones causing gales, including Vance, but there were fourteen cyclones in the previous twenty years. Although the inadequacy of early wind records make it difficult to compare events, it is estimated that there have been four severe cyclones causing winds of at least 170 km/h since 1910: 1945, 1953, 1964 (Katie) and 1999 (Vance).

Along the central Pilbara coast the cyclone season runs from mid December to April peaking in February and March as shown in the graph of monthly occurrence (figure 4).

The development of the offshore oil and gas industries, and more recently, the tourism industry has increased the damage potential of cyclones in the region. Substantial economic losses can be incurred even with the threat of a cyclone impact owing to lost production or disruptions to shipping activities. Fortunately modern structures are built according to cyclone wind ratings and are far less susceptible to damaging winds than those constructed in earlier times.

Figure 1. Satellite image of TC Vance near Exmouth, 22 March 1999. Click on image to enlarge.	Figure 2. Radar image of TC Vance near Exmouth, 22 March 1999. Click on image to enlarge. Click here for more radar images.

Tracks

Cyclones that impact Exmouth typically form over warm ocean waters to the north of the state. The typical steering of these systems is to the southwest and they tend to take a more southerly track as they move further south as shown in figure 3. Some cyclones have originated from near the west Kimberley coast while a few have arrived from the north or northwest. Fortunately cyclones that cross the coast more than 100 km to the east, usually have a minimal impact on Exmouth, for example Orson 1989, Bobby 1995, Olivia 1996, and Monty 2004.

See also the Interactive Tropical Cyclone Plotting web page to access tracks of historical tropical cyclones.

Figure 3. Tracks of notable cyclones affecting the Exmouth region. Click on image to enlarge.	Figure 4. Monthly occurrence of cyclones affecting the Exmouth region. Click on image to enlarge.

Flooding

By not being on a major river, Exmouth is not at risk of major flooding caused by rainfall alone. Localised flooding is certainly possible in susceptible areas especially near creeks and low-lying areas. The road link to the south is particularly vulnerable to being cut-off for a period following heavy rain. Major flooding in Exmouth is typically associated with storm surge, as discussed in the next section.

The heaviest rainfall is not necessarily associated with the most intense cyclones but rather with the cyclone's track, speed and areal extent. A tropical cyclone in 1918 caused 377.1 mm over two days at Exmouth Gulf station. Cyclone Rita in 1971 produced 226.6 mm of rain at Learmonth and 194.8 mm at Exmouth. Wind damage was minimal in both of these events.

Storm Surge

Storm surge is a major threat around Exmouth Gulf. Storm surge is a complex function of cyclone intensity and motion, extent of maximum winds, bathymetry and coastline shape. The actual water level, called the storm tide is a combination of the storm surge and tidal variation. The worst case scenario is to have a severe cyclone pass near the town at the time of high tide, in which case the water level will be many metres above the highest astronomical tide. Given the significant tidal variations in the region, this is a rare occurrence. Even with an intense cyclone the highest surge is typically restricted to less than 80 km of the coast owing to the nature of the extent of a cyclone's maximum winds.

The graphic impact of TC Vance on the coast around Exmouth Gulf indicates how a storm surge can change the appearance of the coastline (see TC Vance report (pdf)). However, even during this event it was fortunate the 3.5 m storm surge did not occur at the time of high tide (see storm surge graph).

Some Notable Cyclones Impacting Exmouth