CAT-i Bulletin Catastrophe Information Report Date: December 28, 2018 Sydney Hailstorms, December 20, 2018 Hail Swath for the Sydney Hail Event. Source: Dr Joshua Soderholm, Monash University, using radar data from the Australian Bureau of Meteorology. Summary A severe convective storm affected large parts of New South Wales, including Sydney, the Central Coast, and Wollongong from 4:00 to 7:00 pm on December 20, 2018. The storm generated large hail, damaging winds, and flash flooding in many areas of the state. According to the Australian Bureau of Meteorology (BOM), there were ground reports of hail of 8 cm diameter in Berowra Heights in Sydney s north and similar size hail in Casula and Liverpool in the city s southwest. The Nattai National Park west of Picton also experienced large hail. Initial damage reports indicated that the suburbs of Berowra Heights, Hornsby, Liverpool, Gosford, and Lithgow were the most severely affected. Given that the event occurred during the Christmas holidays, many residents and businesses have not fully assessed the extent of damages; therefore, loss estimates are expected to increase in the next few weeks.
Meteorological Discussion The BOM issued severe storm warnings in the afternoon of Thursday, December 20 across large parts of the state of New South Wales, including Sydney, the Hunter Valley, Newcastle, Wollongong, and Dubbo. Multiple storm cells tracked across Sydney and the Central Coast from 4:00 to 7:00 pm local time. The initial storm cells moved in a westerly direction across Sydney s southwest suburbs around 4:30 to 5:00 pm (shown below left). The southern storm cell moved across Liverpool and Bankstown around 5:00 pm, and then moved across the Northern Beaches at about 5:30 pm. The northern cell tracked toward Hornsby and then northwest toward Berowra Heights and Cowan, where it appeared to intensify, with larger hail. This cell then continued to track toward Gosford in the Central Coast. Estimated Rain Rate at 4:30 pm (left) and 6:30 pm (right), based on Sydney (Terry Hills) Radar Loop. Source: BOM Another series of storm cells developed around 5:30 pm over the southwest of Sydney and the Central Coast. The first cells with hail developed over Lucas Heights, and then moved over Sydney airport at about 6:00 pm. In the north, a second storm cell intensified with hail and moved across Gosford around 6:00 pm. Subsequently, another cell developed over Sydney s southwest, passing over Liverpool and Homebush at about 6:30 pm (shown above right). The front page of this report shows an image of the preliminary Maximum Estimated Hail Size (MESH) mapping developed by Dr. Joshua Soderholm of Monash University using the radar data from the BOM. The hail size estimates are based on a hail algorithm applied to radar scans from the Wollongong radar, with a minimum hail size threshold of 2 cm. MESH is estimated based on radar reflectivity in the thunderstorm clouds, and may therefore vary in size and in space to the actual hail recorded on the ground. The map shows the largest estimated hail in the atmosphere occurred around Berowra in Sydney s north and Liverpool in Sydney s southwest.
In addition to hail, significant rainfall was recorded across the Sydney basin and Central Coast regions (shown below left). According to BOM, rainfall totals exceeded 25 mm in several areas of southern Sydney and the Central Coast. The rainfall produced flash flooding in several locations, including multiple points along the Great Western Highway, Macquarie Street in Windsor, and Warringah Road at the Roseville Bridge. There were also reports of damaging wind gusts of more than 140 km/hr at Narrabri and Wee Waa on the northwestern slopes, while Murrurundi and Scone reported wind gusts of 114 km/hr and 111 km/hr, respectively. The figure shown below right shows the wind gusts measured by Doppler Radar from Sydney (Terry Hills). Rainfall Estimates (left) and Doppler Wind Estimates (right). Source: BOM Following the Sydney event, several thunderstorms affected Brisbane and the Gold Coast on Friday, December 21 and Saturday, December 22.
Impacts The BOM has described the storm as the worst hailstorm in 20 years. The largest hail loss occurred on April 14, 1999, which affected large areas of Sydney s eastern suburbs with maximum hail sizes of 9.0 cm and a normalized loss of around AUD 5.6 billion (Table 1 below). Based on initial media reports, many homes and businesses have sustained damage to roofs, awnings, and solar panels. Additionally, overflowing gutters caused interior damage to some properties. For motor, initial damage reports indicate that many windshields were smashed, and cars have been impacted by flash flooding. Meanwhile the events of December 21 and 22 produced loss of power to around 45,000 homes and some hail damage to homes and cars. However, impacts appeared to be more limited than those from the Sydney event. The Insurance Council of Australia (ICA) has issued declared postcodes for claims collection. The declared list includes 541 postcodes covering large parts of New South Wales. According to the ICA, the NSW Office of Emergency Management (OEM) has established information points in Berowra Heights and Chipping North to assist with recovery. In terms of insured losses, the event remains in the early stages of development. The ICA reported that insurers received around 45,000 claims by 8:00 am on December 22, with an estimated loss of approximately AUD 210 million. About three-quarters of these claims are from motor. This loss estimate is expected to rise over the next few weeks, in part because many are traveling and businesses are closed for the holiday period. The table below provides a comparison of maximum reported hail sizes and loss estimates for historic hail events, based on the ICA disaster statistics. Comparison of reported hail sizes and insured losses for historic hail events Source: ICA. Hail Event Max Reported Hail Size (cm) Original Loss Normalized Loss ($) 4 ($) 4 April 14, 1999 Sydney 9.0 1.7 B 5.6 B March 18, 1990 Sydney 8.0 0.32 B 1.68 B December 9, 2007 Blacktown 8.5 0.42 B 0.59 B March 6-7, 2010 Melbourne 10.0 1.04 B 1.63 B March 21-22, 2010 Perth 6.0 1.05 B 1.34 B November 27, 2014 Brisbane 8.0 1.39 B 1.54 B December 20, 2018 8.0 Sources: Australian Bureau of Meteorology, Insurance Council of Australia, ABC News, SBS News, the Australian, Reinsurance News.
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