Severe Tropical Cyclone Vance16 March 1999 - 23 March 1999 |
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Severe Tropical Cyclone Vance 16 March 1999 - 23 March 1999 © Commonwealth of Australia, March 2000. This work is copyright. Apart from any use as permitted under the Copyright Act 1968, no part may be reproduced by any process without prior written permission from the Bureau of Meteorology.
Department of the Environment and Heritage |
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Overview of Severe Tropical Cyclone Vance16 March 1999 - 23 March 1999 On the 22 March 1999 one of the strongest cyclones ever to affect mainland Australia crossed the Pilbara coast of Western Australia near the town of Exmouth. By the time Tropical Cyclone (TC) Vance had weakened to below cyclone strength on the 23 March it had wreaked a trail of destruction stretching from Exmouth in the Pilbara to Kalgoorlie in the Goldfields. Its effects were also felt in the Great Australian Bight and parts of South Australia and Victoria. About 10% of the buildings in Exmouth suffered severe structural damage, though many more experienced less obvious damage due to intrusion of rainwater. Water and power supplies throughout the Gascoyne and Goldfields were disrupted and many homesteads sustained wind or flooding damage. The main rail and road links to the eastern states were cut. The 1998/ 1999 tropical season was an extremely active one. Vance was just one of six cyclones to develop in the waters off the northwest coast of Western Australia. The Bureau of Meteorology's tropical cyclone warning service performed well under this intense pressure, particularly during TC Vance. |
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TC Vance's lifespanVance began its life as a low in the Timor Sea. It was named by the Darwin Tropical Cyclone Warning Centre during the afternoon of 18 March. Vance started moving quite steadily westsouthwest at first, slowly intensifying to Category 3 strength late on 19 March. It headed southwest during 20 and 21 March, and was upgraded to Category 5 during the night. At this highest category it was capable of producing very destructive wind gusts of more than 280 km/ h. The central pressure of Vance was estimated to be near 910 hectoPascals.Late on 21 March Vance changed track to a due southerly course, heading directly towards the Exmouth/ Onslow area. The Perth Tropical Cyclone Warning Centre issued its first warnings of the possibility of a cyclone impact in the Exmouth/ Onslow area during the morning of Saturday 19 March, more than 36 hours before the onset of gale force winds. Consequently the community was well prepared. During Monday morning (22 March) the eye of Vance passed down Exmouth Gulf, about 25 kilometres to the east of Exmouth and 80 kilometres to the west of Onslow. A record wind gust speed for the Australian mainland of 267 km/ h was recorded at the Learmonth Meteorological Office, 35 kilometres south of Exmouth shortly before midday. At Onslow the maximum gust recorded was 182 km/ h. 
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The storm surge associated
with Vance caused severe
erosion of the beachfront
and marina at Exmouth and
stranded three large barges
on the edge of Beadon Creek
at Onslow. The cyclone crossed the southern part of Exmouth Gulf around 1pm on 22 March, then continued further inland and slowly weakened. The remnants of Vance moved into the Bight east of Esperance and produced gale force winds over parts of South Australia and Victoria late on 24 March. Severe house damage in Exmouth. The effects of a category 5 cyclone on the Exmouth Caravan Park. The residents of Exmouth begin the long clean up ...a recordwind gust forthe Australianmainland of267 km/h... |
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Monitoring the progress of TC VanceMore than half of Western Australia's coastline, together with a large proportion of our industry, is vulnerable to the threat of tropical cyclones. The Bureau's three Tropical Cyclone Warning Centres (TCWC)Ñ located in Perth, Darwin and BrisbaneÑ maintain a close watch for the formation of cyclones. The Perth Tropical Cyclone Warning Centre's area of responsibility stretches north to Indonesia and west to the central Indian Ocean. The two main detection systems used by meteorologists to track tropical cyclones are satellites and radars.Satellite images High resolution satellite images are received every hour from the Japanese Geostationary Meteorological Satellite. These images are artificially enhanced with various colours corresponding to temperature ranges and vertical heights in the atmosphere. The different colour patterns on an enhanced satellite image are used by a meteorologist to help determine the intensity of the cyclone. If the cyclone is located well out to sea, with no ship or aircraft nearby to provide observations, this technique may be the only one available to determine its intensity. With the aid of satellites, location errors in positioning cyclones have been reduced to about 60 kilometres or even less with a well-defined eye. Satellite image at 10: 30am 22 March 1999 showing the eye of cyclone Vance in Exmouth Gulf.  |
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Weather watch radarWhen a cyclone comes within about 250 kilometres of the Western Australian coastline its track can be monitored by one of the Bureau's weather watch radars at Broome, Port Hedland, Karratha, Learmonth or Carnarvon. These radars detect the intensity of rain from the strength of the echoes. The radar images are updated every 10 minutes and give a picture of the rainfall rates associated with the approaching cyclone. With a good eye visible on radar it is possible to locate the cyclone centre to within 20 kilometres.The weather radar at Learmonth provided the Perth TCWC with invaluable information on the position of TC Vance as it approached the coast. Learmonth radar image at 10: 10am 22 March 1999 showing the eye of Vance entering Exmouth Gulf.  |
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Pressure and wind at landfallThe eye of TC Vance passed across Exmouth Gulf on Monday morning 22 March. At the Learmonth Meterological Office, about 35 kilometres south of Exmouth, the winds increased in speed during the early hours of 22 March and blew greater than gale force (63 km/ h) for a period of about 12 hours starting around 5 am. At the height of the storm the average wind speed was close to 180 km/ h. A record wind gust speed for the Australian mainland of 267 km/ h was recorded at the Learmonth Meteorological Office shortly before midday.Graph showing the wind speed (top) and direction (bottom), at Learmonth from 2: 25am to 9: 40pm on 22 March 1999.  |
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The lowest barometric pressure recorded at
Learmonth was 937.8 hPa at around
11. 30am. At Onslow the maximum gust
recorded was 182 km/ h and the lowest
pressure was 978.2 hPa.
By the morning of the 23rd Vance had been
downgraded to a category 2 cyclone and was
moving through the GascoyneÐ Murchison
districts towards the southeast at 50 km/ h.
Meekatharra registered mean wind speeds of
78 km/ h with gusts to 96 km/ h. Buildings,
windmills, animal feed, roads and other rural
infrastructure were damaged by the wind
and rain.
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Tropical cyclone storm surgePotentially the most destructive phenomenon associated with cyclones that make landfall is the storm surgeÑ a raised mound of seawater typically some 50 kilometres across and up to several metres higher than the normal tide. The storm tide is the combined height of the astronomical (or normal) tide and the storm surge. The worst possible scenario arises when a severe cyclone crosses a coastline with a gently sloping seabed at or close to high tide. Wave action on top of the storm tide can raise the water level even further producing a battering effect on vulnerable structures.At Exmouth, during Vance, the storm surge was measured to be 3.6 metres and caused severe erosion of the marina and inundation of the beachfront. At Onslow, where the storm surge was estimated to be 4 metres, three large barges were stranded on the edge of Beadon Creek. The lower parts of the town were inundated by seawater. Graph showing the height of the storm surge at Exmouth.  |
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The maximum storm surge, estimated to be more than 5 metres occurred on the coast west of Onslow. Aerial photographs of this region show that severe scouring of coastal dunes occurred. At Tubridgi Point (on the northeast tip of Exmouth Gulf) the very destructive signs of the storm surge were vividly apparent. The severe coastal erosion and widespread denudation of vegetation had completely transformed the landscape.
The eerie landscape at Tubridgi
Point following a massive storm surge.
Aerial photo looking west from
Onslow showing the severe erosion and
scouring of dunes by the storm surge.
A storm surge estimated at more than
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Rainfall and flooding summaryThe map below shows rainfall figures of 100 - 150 mm with some areas receiving 200 - 300 mm near the location where the cyclone made landfall. Rainfall totals in the area southeast of Exmouth may be underestimated. Rainfall figures of 50 - 100 mm were recorded along the path of the cyclone through the Gascoyne and down to the east of Esperance.Flooding caused many problems to power supplies and communication links through the Gascoyne and many homesteads were either flooded or cut off. In the Goldfields the main highway and the rail link to the eastern states were cut by floodwaters.  |
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The Western Australian Tropical Cyclone Warning SystemDuring a cyclone event the following services are provided by the Perth Tropical Cyclone Warning Centre:
Cyclone Severity CategoryAn estimate of cyclone intensity is included in all Tropical Cyclone Advices. Categories of cyclone severity range from "1" for a relatively weak cyclone to "5" for the most severe. Category 3, 4 and 5 are classified as "severe" with hurricane force winds. |
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Standard Emergency Warning SignalThe Standard Emergency Warning Signal (SEWS) is sounded by radio stations prior to reading out the tropical cyclone warning for a category 2 or higher cyclone.How to access TropicalCyclone information Other than radio and television the Bureau of Meteorology forecasts can be accessed by telephone on 1300 659 210 at the cost of a local call, on Weather-by-Fax or through the internet at http://www.bom.gov.au.The Western AustralianColour Alert System Community alerts are issued by the State Emergency Service (SES) during the tropical cyclone warning period and advise the public of the appropriate actions to be taken as a cyclone approaches. Alerts are issued through radio and television and are displayed in communities using coloured lights or flags. The alert stages are divided into Blue, Yellow and Red.  |
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Tropical Cyclone Tracking MapTracking maps are available to the public and can be used to plot the positions of the cyclone given in the Advices issued by the Bureau of Meteorology. The cyclone tracking maps can be obtained from the State Emergency Service or the Bureau of Meteorology.Tropical Cyclone Threat MapThe Tropical Cyclone Threat Map shows the past track of the cyclone at 12 hour intervals. It also shows the area of gale force winds (gusts > 100 km/ h), destructive winds (gusts > 125 km/ h) and very destructive winds (gusts >170 km/ h) with coloured circles centred on the cyclone. It is available through the internet or Weather-by-Fax.Right: An example of a Tropical Cyclone Track and Threat Map, available from the Bureau of Meteorology. |
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For further information on tropical cyclones in Western Australia, contact the: Bureau of Meteorology PO Box 1370 West Perth 6872 Tel: (08) 9263 2222 or the local Meteorological Offices at Broome, Port Hedland, Learmonth and Carnarvon. http://www.bom.gov.au |
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