It may be thought that tropical cyclones only affect coastal areas of the state. While cyclones certainly weaken as they move inland, the stronger ones remain capable of causing damaging winds for some time before being downgraded below cyclone intensity. A cyclone at category five intensity near the coast capable of causing wind gusts to 300 km/h can still be rated at category three or higher producing wind gusts of over 170 km/h hundreds of kilometres inland. It is quite rare that an inland town experiences the maximum winds of a severe cyclone. The risk of damaging winds also decreases with distance from the coast. Pannawonica, for example, being just 75 kilometres from the coast is much more likely to experience damaging winds than Paraburdoo and Newman which are 300 and 350 kilometres inland respectively. Additionally cyclones weaken at a faster rate when moving over hills and mountains such as the Hamersley and Chichester Ranges compared to those moving over flatter terrain over the eastern Pilbara and Great Sandy Desert areas.
Typically the greatest impact of most cyclones inland is flooding from heavy rainfall. This can cause damage to buildings and fences near watercourses in addition to road and rail networks. The added cost of transport delays can cause significant economic costs particularly to the mining industry. Some of the more remote communities may be isolated for extended periods before water levels fall and roads and bridges repaired. While most towns and communities are located away from flood-susceptible areas, some such as Nullagine often experience flooding in the town.
The tracks of cyclones affecting inland Pilbara are similar to those affecting coastal communities of Port Hedland, Karratha/Dampier, and Onslow. These cyclones typically form over warm ocean waters to the north of the state and intensify before crossing the coast, by which stage they are moving in a general southerly track. The further south cyclones move the more likely they will take a southeasterly track across inland parts of the State.
Tropical cyclone Olivia is one example of a severe cyclone that crosses the Pilbara coast and, while weakening, can still cause damage to inland parts.
See the Interactive Tropical Cyclone Plotting web page to access tracks of historical tropical cyclones.
Heavy rainfall and associated flooding is the main impact for most cyclone events in the inland Pilbara. The highest rainfall is usually found along or just east of the track for most systems. The flood potential of a system is not directly related to cyclone intensity but is associated with its track, speed, areal extent and saturation of catchments from prior rainfall. Indeed rainfall totals in excess of 100 mm are common with tropical lows that move over land. In February 1997 a slow moving low moved over the west Kimberley, Pilbara and Gascoyne causing rainfall in excess of 400 mm in parts and one of the highest ever floods along the Ashburton River. Cyclone Joan in December 1975 caused over 400 mm of rain near its track, the highest fall being 591 mm at Marandoo.
Flooding is enhanced when multiple tropical lows occur within a few weeks of each other. During January and February 1961 rainfall totals exceeded 200 mm during two tropical cyclones. At Wittenoom it was described as the worst flood in memory as water levels rose to 23 m in sections of the Gorge. In both events Wittenoom was isolated. In 1980 cyclones Amy, Dean and Enid moved over the eastern Pilbara causing total rainfall to exceed 600 mm in some areas.
Some Notable Cyclones Impacting inland Pilbara towns
|Tropical Cyclone||Impact Description|
At Marble Bar several houses collapsed and five windmills were blown over. All houses in the town were damaged, the Post Office and its residence seriously.
At Nullagine buildings were extensively damaged especially the hotel. Many windmills destroyed and station property wrecked at Mount Edgar Station.
|28 Dec 1930||Considerable damage was done to the Marble Bar courthouse residences, Police Station and Post Office. Residents claim the blow was the worst ever experienced. At Nullagine the river rose higher than on any previous occasion and the Post Office was flooded. The surrounding country was inundated. Corruna Downs station sustained considerable damage and heavy floods.|
|1-2 Mar 1941||
At Marble Bar few buildings escaped damage and some lost their roofs. The Courthouse was partly unroofed, as were the Post Office, Police Station and Hospital.
Storm water damaged many building interiors. At the Comet Mine a number of buildings were flattened and sheeting was lost from others. A total of 305 of rain fell in the town and two cars were reportedly blown into the flooded creek that ran through town.. One man was injured by falling timber as he attempted to secure his roof.
The railway was severely damaged. At Warralong Station where the eye passed over at 11 pm all buildings and windmills were badly damaged and east - west fences destroyed.
|Jan/Feb. 1961||Two cyclones within a month combined to caused massive flooding in the vicinity of Wittenoom.|
|Shirley 2 Apr 1966,||Shirley passed crossed the coast at King Bay where a ship recorded winds to 204 km/h. Sherlock station recorded 404 mm and subsequent floodwaters damaged the Mount Goldsworthy and Hamersley iron-ore railways under construction, roads and other facilities along the Northwest coast.|
|Joan, 8 Dec. 1975||Apart from badly damaging Port Hedland Joan caused heavy rain over over 400 mm near its track. Marandoo recorded a total of 591 mm of rain. Stock losses were heavy with most stations between Wittenoom and the coast. thousands of kilometres of fencing were destroyed in the floods. The Circular Pool tourist attraction at Dales Gorge severely eroded, completely changing the nature of the area.|
|Amy, 10-11 Jan 1980||
Amy crossed the coast near Pardoo Station about 110 km east of Port Hedland at 10am on the 10th a central pressure of 915 hPa. Six hours later Amy passed very close to the mining town of Goldsworthy where a mean sea level pressure of 932 hPa was recorded and gusts were estimated at 200-240 km/h. Severe damage to company housing, buildings and mining equipment was the beginning of the end for Goldsworthy which has since been dismantled.
Total losses, including property damage and industrial disruption, were estimated at around $25 million. No lives were lost, nor injury sustained.
|Enid, 17 Feb. 1980||After crossing the coast near Wallal station Enid passed within 30 km of Shay Gap at 7 am causing severe damage to blocks of flats and houses which were unroofed.|
|Ilona, 18-19 Dec. 1988||Ilona crossed the coast early on the 18th and although weakening still caused damage to Pannawonica and Tom Price. The cyclone brought much needed rain to most of the Pilbara and produced record December rainfall totals in central parts of the state.|
|Orson, 22 April 1989||Orson crossed the coast near Cape Preston, 56 km west of Dampier having an estimated pressure of 920 hPa. Although weakening, Orson caused widespread structural damage at Pannawonica.|
|Bobby, 10 - 11 April 1995||Bobby crossed the coast just to the east of Onslow between midnight and 1 am on the 25th. Pastoral stations along the track between Onslow and Gascoyne Junction reported property damage. Very heavy rainfall accompanied Bobby. More than 400 mm of rain fell in the Onslow area during the period of the event. Very heavy rain associated with the cyclone caused serious flooding in the west Pilbara, Gascoyne, Goldfields and Eucla regions. Rainfall associated with this event followed heavy rains over a large part of inland WA earlier in the month.|
|Olivia, 10 - 11 April 1996||Olivia crossed the coast near Mardie causing wind gusts of 257 km/h before accelerating to the southeast. Pannawonica, which is situated 90 kilometres inland from Mardie and recorded gusts to 158 km/h, was extensively damaged. Even as Olivia passed Paraburdoo after midnight, it still produced gusts to 140 km/h.|
|Monty, 1 March 2004||Monty passed over Mardie station to the west of Dampier before passing near Pannawonica where some damage was sustained. Heavy rain flooded rivers. Two people were rescued from the roof of the Yarraloola homestead on the Robe River and the town of Pannawonica was cut-off. A large part of the bridge over the Maitland River on the Northwest coastal highway was washed away.|