Tropical Cyclones Affecting Carnarvon

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It is estimated that a cyclone impact causing wind gusts in excess of 90 km/h in the vicinity of Carnarvon and Shark Bay occurs about once every five years on average. This is less than half the frequency for communities along the Pilbara coast reflecting the decreased risk southwards along the west coast. However, the frequency is not evenly distributed. Since Herbie in 1988 there has only been one cyclone (Frank, 1995) to have caused gales at either Carnarvon or Shark Bay, but there were six cyclone impacts between 1960 and 1970.

In general, cyclones weaken as the move southwards over cooler water and to latitudes where the atmospheric winds are unfavourable for cyclones. Indeed, winds speeds over 170 km/h have only been recorded once, during the March 1960 cyclone when Carnarvon recorded winds of 178 km/h. However, the inadequacy of early wind records makes it difficult to compare events. Other major impacts have been in 1916, 1921, 1934, 1937, 1979 (Hazel) and 1988 (Herbie).

Amongst the earliest accounts of tropical cyclones in Western Australia are those of 1 March 1839, when George Grey's expedition reached Dorre Island off Carnarvon. They reported a sudden drop in wind from the southeast followed by swift onset of northwesterlies, indicating that the eye passed over them. Even the experienced George Grey wrote: 'We all quailed or fell before it , for it come with sudden and indescribable violence'.

Whereas cyclones pose a threat to coastal communities, and in particular the Carnarvon banana plantations and market gardens, pastoralists in the region generally welcome the associated "cyclonic rains" especially after a long dry spell. Inland areas often benefit from systems that have crossed the Pilbara coast and are weakening as the move over the region. However, serious flooding may also result, particularly if heavy rains fall in the catchment areas of the major rivers such as the Gascoyne. Indeed aside from the threat to banana plantations the greatest risk from cyclones at Carnarvon is from potential flooding on the Gascoyne river. The semi-enclosed bays exposed to strong winds increases the risk of Shark Bay to storm surge.

Cyclones have occurred from December to May although they are most frequent in February and March as shown in the graph of monthly occurrence.

Photo 1. The wreckage of the Korean Star at Cape Cuvier, north of Carnarvon, following Herbie in 1988.

Photo reproduced courtesy of The West Australian.

Tracks

Cyclones that impact Carnarvon 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 the tracks of all cyclones that have moved within 100 km of the town. Fortunately cyclones that cross the coast to the north, usually have a minimal wind impact on Carnarvon. These systems usually produce heavy rain inland.

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

Figure 2. Tracks of notable cyclones affecting Carnarvon/Shark Bay. Click on image to enlarge.

Figure 3. Monthly occurrence of cyclones in Carnarvon. Click on image to enlarge.

Flooding

Potentially the greatest cyclone-related threat to Carnarvon is flooding along the Gascoyne River. The heaviest rainfall is not necessarily associated with the most intense cyclones but rather is associated with the cyclone's track, speed and areal extent. Flood events are normally associated with tropical cyclones having crossed the coast to the north and moving inland causing heavy rain over the considerable Gascoyne River catchment area. In 1960 heavy rain from a tropical low over inland areas submerged large areas of country along the Gascoyne River and flooding half of Carnarvon. The extent of flooding is also strongly linked to previous rainfall and existing water levels. In 2000, rainfall events in January, February and then from cyclone Steve in March resulted in major floods along the river.

In the Shark Bay area localised flash-flooding is certainly possible in susceptible areas especially near creeks and low-lying areas. This can make roads impassable for periods.

Figure 4. Inundation of plantations along the Gascoyne River following TC Steve, March 2000. Click on image to enlarge.

Figure 5. Severe erosion along South River Road in Carnarvon following TC Steve, March 2000. Click on image to enlarge.

Photos courtesy of WA Department of Environment.

Storm Surge

Storm surge is a major threat around Shark Bay in particular. In 1937 high seas and an estimated 4.3 m tide, associated with a cyclone passing offshore, resulted in 14 km of the Hamelin Pool - Denham road being covered with water. In February 1921 a storm surge pushed sea water 2.9 m above the highest tide mark at Denham, resulting in 20 cm of water in the Post Office. The whole town was inundated and from 3:30 pm until midnight on the 20th, the population had to shelter in the School and Police Station.

Historically storm surge has affected Carnarvon, such as in March 1934. However, since then flood mitigation works has decreased the risk of storm surge risk to the town.

Some Notable Cyclones Impacting Carnarvon and Shark Bay

Tropical CycloneWind Gust (km/h)Impact Description
28 Feb- 1 March 1839- At Dorre Island, George Grey's expedition to the Northwest encountered the full force o f a cyclone. At 5:30 am on the 1st the wind suddenly dropped and then shifted instantaneously to the northwest, coming with 'indescribable violence'. Not a tree was left standing on the island and the sea rose 48 metres beyond the high water mark on the beach.
24-25 Feb. 1893- A cyclone passed down the west coast. At Shark Bay, eight cutters were damaged, two being smashed to pieces. High tides flooded many houses.
19-20 Jan 1916130 est. A cyclone moved down the west coast, crossing the coast near Shark Bay on the morning of the 20th when it caused gales and very high seas. At Carnarvon, the Boy Scouts Hall was flattened as were trees, fences and crops. Shark Bay recorded 132 mm of rain.
19-20 Feb. 1921- Gales caused damage at Carnarvon on the morning of the 18th, but the damage was greatest at Shark Bay where eight fishing boats were destroyed and eight were driven ashore, including the steamer Torrens, trees were uprooted and houses were unroofed. Two people died when a boat was destroyed at Dirk Hartog Island. A storm surge pushed sea water 2.9 m above the highest tide mark at Denham, resulting in 20 cm of water in the Post Office. The whole town was inundated and from 3:30 pm until midnight on the 20th, the population had to shelter in the School and Police Station.
6-7 Mar 1934140 est. A cyclone caused considerable damage at Carnarvon including the demolition of the Yankeetown Mechanics Institute. The high tide flooded Olivia Terrace for many metres. At Shark Bay, a 7 tonne lugger capsized while four others were dragged out to sea.
9 Feb. 1937- At Shark Bay a cyclone destroyed many boats and caused a tidal surge to inundate low-lying areas. Some Denham houses were under about 2 m of water and residents had to row to safety. Waves broke to the steps of the Dirk Hartog Island homestead and the 10 tonne cutter Dirk Hartog was driven over 100 m up the beach. Huge seas combined with a 4.3 m tide to alter the coastline for several kilometres and cover 14 km of the Denham road.
27-28 Feb. 1943130 est. A cyclone struck Carnarvon before dawn on the 28th destroying banana plantations and other properties. The Gascoyne River flooded Carnarvon causing more property damage on 2 March.
23 Mar. 1953120 est. Banana plantations were wrecked, windmills and telegraph lines blown down and houses and offices wrecked. Damage was estimated at 250,000 pounds.
26 Mar. 1960178 Hundreds of people were left homeless as structures were destroyed or unroofed. An estimated 500,000 pounds damage was caused, half of which was to the banana industry.
Ingrid 15-17 Feb. 1970132 Some houses were unroofed, five caravans were overturned, power lines brought down and citrus and banana crops were destroyed.
Beverley, 31 Mar. 1975111 At Quobba station, winds to 160 km/h caused $600,000 damage. Three prawn trawlers were washed ashore. Up to half the Carnarvon banana crop was ruined.
Hazel, 13 Mar 1979137 Hazel passed 80 km west of Carnarvon before making landfall at Shark Bay at about midnight. The Carnarvon Hotel was unroofed and damage to bananas was estimated at $2 million. A storm surge at Denham flooded buildings forcing people to evacuate.
Herbie, 21 May 1988121 Herbie rapidly accelerated to the southeast at speeds reaching 75 km/h before passing over Denham at 6:45 am. Structural damage extended to Carnarvon, while further north at Cape Cuvier, the Korean Star, a 30,000 tonne freighter was wrecked. A 2 m storm surge flooded the Denham foreshore.