Cyclone Althea

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Severe Tropical Cyclone Althea
Category 4 severe tropical cyclone (Aus scale)
Satellite image of a tropical cyclone near the northeastern coast of Australia. Curved rainbands are shown but no eye is visible.
Satellite image of Cyclone Althea on 23 December
Formed19 December 1971 (19 December 1971)
Dissipated29 December 1971 (29 December 1971)
Highest winds10-minute sustained: 165 km/h (105 mph)
Lowest pressure952 hPa (mbar); 28.11 inHg
Fatalities2 direct, 1 indirect
Damage$120 million (1971 AUD)
Areas affectedQueensland
Part of the 1971–72 Australian region cyclone season

Severe Tropical Cyclone Althea was a powerful

landfall was monitored closely by land-based radar that depicted an ongoing eyewall replacement cycle
. Althea produced copious rainfall over central and western Queensland as it turned toward the southeast, and on 26 December the cyclone emerged over open waters. After briefly re-intensifying, the system dissipated on 29 December.

While moving ashore, Althea generated wind gusts as high as 215 km/h (134 mph) that wrought significant destruction around Townsville and left nearby

AUD
).

Meteorological history

Map of eastern Australia and the western South Pacific Ocean with a color-coded track that shows the path of the cyclone
Map plotting the storm's track and intensity, according to the Saffir–Simpson scale
Map key
Saffir–Simpson scale
  Tropical depression (≤38 mph, ≤62 km/h)
  Tropical storm (39–73 mph, 63–118 km/h)
  Category 1 (74–95 mph, 119–153 km/h)
  Category 2 (96–110 mph, 154–177 km/h)
  Category 3 (111–129 mph, 178–208 km/h)
  Category 4 (130–156 mph, 209–251 km/h)
  Category 5 (≥157 mph, ≥252 km/h)
  Unknown
Storm type
triangle Extratropical cyclone, remnant low, tropical disturbance, or monsoon depression

Cyclone Althea originated in an expanding area of thunderstorm activity near the

UTC on 20 December, less than 300 km (200 mi) southwest of Honiara.[3] Just after 23:00 UTC on 21 December, imagery from the United States ESSA-8 satellite showed the first indications of an emerging eye feature. Althea tracked southwest toward the coast of Queensland around a subtropical ridge to the south, and steadily strengthened.[4] Near 18:00 UTC on 22 December, it reached its peak intensity with 10-minute maximum sustained winds of 130 km/h (80 mph); this made it a Category 3 severe tropical cyclone on the Australian scale.[3] The cyclone's central barometric pressure of 952 hPa (28.1 inHg) was estimated using the lowest recorded air pressure, 971.5 hPa (28.69 inHg) at Townsville Airport, a 32 km (20 mi) radius of maximum wind, and environmental air pressures.[4]

Image of a radar scan showing the cyclone's core. Concentric eyewalls are shown with a small ring at the center of a larger circular void
Radar image of Althea just before landfall, showing concentric eyewalls

Late on 22 December, the eye remained obscured to satellite imagery by a

high pressure area to the south, gale-force winds extended well to the south of the cyclone's centre. While the system was moving ashore, land-based radar imagery identified an ongoing eyewall replacement cycle, with two distinct, concentric eyewalls – rings of intense thunderstorms surrounding the centre. The strongest winds were found under the contracting outer ring, which shrank from 55 to 39 km (34 to 24 mi) between 21:00 and 23:00 UTC to become the dominant eyewall as the inner ring dissipated. Consequently, extreme winds initially extended relatively far from the centre.[4]

The storm quickly weakened as it continued southwest, passing just north of Charters Towers City, though it continued to produce heavy rainfall over interior Queensland.[1][5] Curving southeastward, Althea re-emerged over open waters between Maryborough and Double Island Point on 26 December and began to intensify once again.[2] At 00:00 UTC on 28 December, the cyclone reached a third peak with 10-minute winds of 110 km/h (70 mph), but as it turned more toward the south, increasingly cooler sea surface temperatures weakened the cyclone. On 29 December, Althea lost its tropical characteristics over the Tasman Sea.[1][3]

Preparations

In the hours leading up to landfall, the TCWC in Brisbane issued 17 cyclone warnings for coastal areas.[1] According to the BoM, residents received 20 hours of advance warning in which to complete preparations.[6] By late on 23 December, police and state emergency service workers were on alert for the approaching storm.[7] High public preparedness and a relatively low loss of life were attributed to BoM cyclone awareness initiatives in the wake of 1970's deadly Cyclone Ada.[1] However, storm victims still criticised the agency and local radio news stations for unclear, untimely, or conflicting broadcasts that caused widespread confusion.[6] Significant delays between the issuance of warnings from TCWC Brisbane and local broadcast in the Townsville area raised some question about the need for a warning centre closer to North Queensland.[6]

Impact

Total damage from Cyclone Althea amounted to just under A$120 million (1971),[8] and the normalised damage total for 2012, which accounts for growth and inflation, was estimated at $648 million.[9] Throughout the affected region, 257 people were treated for storm-related injuries, mostly inflicted by airborne debris;[10] three people were killed.[8] In Townsville, ten people were reported missing during the cyclone: nine on three boats that were unaccounted for, and one whose car was found in a swollen creek.[11] They were all found safe.[10]

Magnetic Island

An estimated 90% of the buildings on Magnetic Island were damaged to some degree by 215 km/h (134 mph) wind gusts,[2][4] and there was "not a tree left with leaves on it".[12] The island's main town of Picnic Bay was hit particularly hard.[13] About 100 people endured the cyclone in the dining room of a Picnic Bay hotel that ultimately sustained severe structural damage; 65 would remain sheltered there through Christmas Day.[12] Around 60% of houses in Nelly Bay and 40% in Arcadia were demolished.[13] In the village of Horseshoe Bay, one woman died in a building collapse, and reportedly only 8 out of 150 houses in the community survived the cyclone.[14] The island suffered a nearly total power outage, and after the water pipeline from the mainland was damaged, strict usage rations were put in place until repairs could be made.[11][15] About 30 people on Magnetic Island were treated for injuries sustained during the storm,[16] and damage reached $2 million.[12]

Coastal Queensland

Black and white photograph of storefronts with broken windows, some structural damage, and debris littering the sidewalk
Damage to a hotel in Townsville

At the time, Althea was one of the strongest tropical cyclones to strike the coast of Queensland; it still stands as the most intense ever in the Townsville area.

Townsville City Council reported that about 200 houses had been leveled – about 1 in every 100 – with 600 more rendered uninhabitable, and as many as 4,000 damaged.[19] Among the structures damaged or destroyed were 200 Queensland Housing Commission homes and roughly 500 of the 700 War Service Homes Commission dwellings in Townsville.[1][20] Overall, Althea wrought at least $6 million in damage to government-owned buildings.[20] The cyclone killed two people in Townsville: one man was crushed when his home collapsed, and another suffered a stress-related heart attack.[14]

Although the worst of the storm struck near low tide, the combination of a large

beach erosion from Townsville to Toolakea, while north of the storm's center, in the Greater Palm group of islands, substantial erosion resulted from southwesterly winds.[4] Beaches receded by as much as 15.8 m (52 ft) between Pallarenda and Rowes Bay, and by up to 12 m (39 ft) at Balgal Beach near the cyclone's landfall point.[17] Storm surge values tapered off sharply to the north of the storm centre, but remained high well to the south, with above-normal water levels extending as far south as Mackay.[21]

At

Pallarenda, the storm surge swept vehicles off roads and inundated homes;[1] around 40% of dwellings were rendered uninhabitable. Trees and power lines in the community were mangled, nearly every building was unroofed, and damage amounted to approximately $1 million.[12][22] In Saunders Beach, wind-blown sand debarked trees and buffeted paint from houses.[17] Althea generally dropped 145 to 200 mm (5.7 to 7.9 in) of rain in the Townsville area, much of it falling after the cyclone moved inland.[5] As so many roofs had been damaged, many home interiors were left exposed to the elements. As a result, the deluge caused significant water damage to interior walls, electrical wiring, and personal belongings. Storage facilities at RAAF Garbutt were seriously damaged by the combined wind and rain,[1] and four helicopters at the base were destroyed.[17] In the weeks following the cyclone's passage, further downpours plagued Townsville and triggered flooding when storm drains clogged with debris were unable to handle the runoff.[23] Severe flooding from Althea in the Burdekin River delta was exacerbated by rainfall from Cyclone Bronwyn in early January.[24]

Interior Queensland

Farther inland, up to 250 mm (9.8 in) of rain fell in 12 hours, the most substantial rainfall in 15 years. In some drought-stricken parts of the state, the rain proved beneficial to farmers,[11][16] but there was also widespread flash flooding over western and southern Queensland. Numerous communities were isolated by rising floodwaters, and hundreds of families were forced to evacuate their homes.[1][22] In some cases, residents had to be moved to higher ground by boat, along with any food and provisions they were able to salvage. The overflowing Warrego River washed out parts of the Mitchell and Warrego highways near Charleville,[25] and most of the major roads in western portions of the state were blocked by flooding.[26] Several hundred homes in South West Queensland were inundated. In addition to damaging highways, the cyclone disrupted rail and air transportation.[25] Railroads traveling out of Townsville were submerged under as much as 1.5 m (5 ft) of water, while several airfields were forced to close.[11][26] Later, as the storm approached open water once again, it dropped over 200 mm (7.9 in) of precipitation along the southern coast of Queensland.[5] As runoff from the heavy rains traveled downstream, southern areas continued to experience flooding into early January.[27] Two tornadoes embedded within the cyclone's outer bands touched down in Bowen, causing damage to buildings and vegetation.[2] Damaging thunderstorms in the suburbs of Sydney, on 25 December were broadly attributed to the weather pattern associated with Althea.[28]

Aftermath

Black and white photograph of a contorted single-story home; a crushed automobile is visible beneath the structure
A house in Townsville lifted off its foundation and dropped on a vehicle by the winds

A

Australian federal government reimbursed Queensland for an estimated $5.5–6 million spent by the state on recovery.[33]

About 600

retired from the Australian tropical cyclone naming list due to the cyclone's severe impact.[37]

Many of the damaged houses were of poor construction,[12] and in the wake of Althea, engineering studies of the destruction resulted in a new understanding of the structural design loads necessary to withstand severe winds.[38][39] In particular, inadequate roof cladding and fastening systems were among the primary points of failure.[40] Consequently, much stricter building codes were explored in Queensland and Australia as a whole.[41] Three years later, Cyclone Tracy's devastation in Darwin, Northern Territory, bolstered the trend of more rigorous construction specifications in the country.[38] Many of the buildings destroyed by Tracy were government housing units constructed according to new guidelines based on findings after Althea, showing the need for further study.[40] The severe cyclones prompted Queensland to develop its first statewide building regulations in 1975; the new Queensland Home Building Code was fully adopted in the mid-1980s.[40] Under the new regulations, roofs had to be more securely anchored than before using bolts and reinforced fastenings.[13][42] Having seen the dangers of deficient construction first-hand, Townsville was the first community to enact the enhanced building standards, and served as a testing ground for further revisions.[40][43] The Cyclone Testing Station, a wind damage research organisation housed within James Cook University's Townsville campus, was established in 1977 in response to cyclones Althea and Tracy.[44]

See also

References

  1. ^ a b c d e f g h i j k l m n o p Bureau of Meteorology (July 1972). "Report by Director of Meteorology on Cyclone Althea" (PDF). Australian Government Publishing Service. Archived (PDF) from the original on 20 March 2012. Retrieved 1 March 2017.
  2. ^ a b c d e f g h "Severe Tropical Cyclone Althea Summary". Bureau of Meteorology. Archived from the original on 31 March 2017. Retrieved 1 March 2017.
  3. ^ a b c d International Best Track Archive for Climate Stewardship. "1972 09P Althea (1971354S11159)". University of North Carolina, Asheville. Archived from the original on 9 March 2017. Retrieved 1 March 2017.
  4. ^ a b c d e f g h Callaghan, Jeff (22 September 2011). "Case Study: Tropical Cyclone Althea, 1971" (PDF). Green Cross International. Archived (PDF) from the original on 22 August 2016. Retrieved 4 March 2017.
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  6. ^ a b c Fielding, Trisha (19 December 2015). "The cyclone that tore up the city on December 24". Townsville Eye. p. 26 – via InfoTrac.
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  8. ^ a b Centre for Research on the Epidemiology of Disasters. "EM-DAT: The Emergency Events Database". Université catholique de Louvain.
  9. ^ "Cyclone Althea, Queensland 1971". Australian Disaster Resilience Knowledge Hub. Archived from the original on 14 April 2017. Retrieved 13 April 2017.
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  16. ^ a b c d "Long recovery road". The Canberra Times. 28 December 1971. p. 1. Archived from the original on 9 March 2017. Retrieved 6 March 2017 – via Trove.
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  29. ^ a b "Storms cause damage in two states and A.C.T." The Canberra Times. 27 December 1971. p. 1. Archived from the original on 12 March 2017. Retrieved 6 March 2017.
  30. ^ a b Hodgkinson, Jan (26 June 1973). "Army helps when disaster strikes". The Canberra Times. p. 13. Archived from the original on 12 March 2017. Retrieved 9 March 2017 – via Trove.
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  32. ^ a b c "Individual grants for cyclone repairs". The Canberra Times. 31 December 1971. p. 6. Archived from the original on 12 March 2017. Retrieved 6 March 2017.
  33. ^ "Disaster relief". The Canberra Times. 17 February 1972. p. 1. Archived from the original on 12 March 2017. Retrieved 6 March 2017 – via Trove.
  34. ^ "Cyclone relief committee to distribute funds". The Canberra Times. 29 December 1971. p. 3. Archived from the original on 12 March 2017. Retrieved 6 March 2017 – via Trove.
  35. ^ "Cyclone Althea". Monument Australia. Archived from the original on 12 March 2017. Retrieved 4 March 2017.
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  37. ^ RA V Tropical Cyclone Committee (12 December 2012). "List of Tropical Cyclone Names withdrawn from use due to a Cyclone's Negative Impact on one or more countries" (PDF). Tropical Cyclone Operational Plan for the South-East Indian Ocean and the Southern Pacific Ocean 2012 (Report). World Meteorological Organization. pp. 2B–1. Archived (PDF) from the original on 12 May 2013. Retrieved 6 March 2017.
  38. ^ a b Andersen, John (24 December 2011). "Cyclone Althea: December 24, 1971". Townsville Bulletin. p. 20 – via InfoTrac.
  39. ^ "Australian Achievements in the Mitigation of Wind Damage to Housing from Tropical Cyclones" Archived 12 March 2017 at the Wayback Machine. Walker, George R. 17 October 1991.
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  41. ^ Pearce, Tony (November 2008). "Assessing risk". The Australian Journal of Emergency Management. 24 (4). Archived from the original on 19 February 2017. Retrieved 5 March 2017.
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  43. ^ Leitch, C.; et al. (January 2011). "Performance of housing in Brisbane following storms on 16 November 2008". Australian Journal of Structural Engineering. 12 (1): 45–62.
  44. ^ "History of the Station". James Cook University. Archived from the original on 13 April 2017. Retrieved 12 April 2017.

External links

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