Severe Tropical Cyclone Yasi: One of the most powerful cyclones to affect Australia
The vulnerability of Queensland to storm surges
Queensland, Australia is vulnerable to storm surges due to the combination of: (1) the relatively high frequency of tropical cyclones; (2) wide continental shelf which can amplify surges; and (3) many low-lying cities and towns (Griffith University, n.d.). Most tropical cyclones impact the northern areas of Queensland, but they can affect southern areas as well. On average, there are 4.7 tropical cyclones per year in Queensland and they mostly occur during November and April (BoM, 2015a).
Development and progression of TC Yasi
Severe Tropical Cyclone (TC) Yasi is one of the largest measured cyclones to reach the Australian coast. It started as a tropical low northwest of Fiji on 29 January 2011, and started moving westward (BoM, 2015b). The low rapidly intensified and reached cyclone status north of Vanuatu. TC Yasi continued to track westward, then west-southwest towards Queensland, and rapidly increased in intensity to reach marginal Category 5 at 4 am on February 2 (BoM, 2015b). TC Yasi made landfall on Mission Beach, Queensland, around 12 am – 1 am on 3rd February, and travelled across northern Queensland before weakening to a tropical low near Mount Isa at 10 pm on 3 February (BoM, 2015b). TC Yasi was a large system, with an eye of more than 100 km wide, and a storm diameter of 600 to 800 km (Little et al., 2012). It was compared to being a similar size and power to Hurricane Katrina (e.g. BBC, 2011), and was large enough to swamp the UK.
Source: BBC (2011)
The storm surge
TC Yasi made landfall at South Mission Beach, as a marginal Category 5 system. Wind gusts reached up to 286 km/hr. If TC made landfall at high tide, the storm tide was forecast to reach 7 m (Little et al., 2012). However, the highest storm surge recorded was 5.33 m above the predicted tide at Cardwell. This was because fortunately, the landfall at TC occurred around low tide, so the maximum storm tide level was 4.5 m about mean sea level. Queensland has a network of 25 tide gauges (insert hyperlink: https://www.qld.gov.au/environment/coasts-waterways/beach/storm-explained/) that monitored sea levels during the passage of TC. One tide gauge (Lucinda) was destroyed during the cyclone (Queensland Government, 2012).
There was widespread evacuation throughout Queensland (Daily Telegraph, 2011) leading up to the landfall of TC Yasi, including of two hospitals located on the water front (Little et al., 2012). IN a review of the damage from TC Yasi, the Queensland Government (2012) summarized the occurrence of coastal flooding inundation during high tide, on the late morning on 3 February, between Cairns and Townsville. Damages were recorded to vegetation, roads, sea walls, buildings, and beach erosion. At Hull Heads, the storm surge reached up to 100 m inland from the foredune, and washed away homes. However, it is not known if this localized inundation was due to the storm surge, or due to higher estuarine water levels due to the rainfall associated with TC. Near Caldwell, the Port Hinchinbrook Marina and millions of dollars’ worth of yachts were destroyed and the Lucinda Bulk Sugar Terminal was destroyed by the storm surge and waves (Nilsen and Colleter, 2013).
Erosion and road damage at Caldwell. Image by Paul Crock / AFP
Port Hinchinbrook. Image from Brian Cassey, CairnsPost
Bureau of Meteorology (BoM), 2015. Severe Tropical Cyclone Yasi: 30 January – 3 February 2011. http://www.bom.gov.au/cyclone/history/yasi.shtml
Bureau of Meteorology (BoM), 2015. Tropical cyclones in Queensland. http://www.bom.gov.au/cyclone/about/eastern.shtml
Daily Telegraph, 2011. More evacuation centres open in Cairns as North prepares for Cylcone Yasi storm surge. 02/02/2011. http://www.dailytelegraph.com.au/full-house-at-cairns-evacuation-centres-as-townsville-prepares-for-cyclone-yasi-storm-surge/story-e6freuy9-1225998675929
Griffith University, n.d. Storm Surge: You’re your risk in Queensland. https://www.griffith.edu.au/__data/assets/pdf_file/0009/598248/CEMDSS-Storm-Surge-Community-Info-Sheet_Final.pdf
Little, M., Stone, T., Stone, R., Burns, J., Reeves, J., Cullen, P., Humble, I., Finn, E., Aitken, P., Elcock, M. and Gillard, N. (2012), The Evacuation of Cairns Hospitals Due to Severe Tropical Cyclone Yasi. Academic Emergency Medicine, 19: E1088–E1098. doi: 10.1111/j.1553-2712.2012.01439.x
Nilsen, N.O., Colleter, G., 2013. Recovery of the Lucinda bulk sugar terminal post tropical cyclone yasi In: Australasian Port and Harbour Conference (14th: 2013 : Sydney, N.S.W.). Barton, A.C.T.: Engineers Australia, 2013: 606-611.