Yasi Cyclone

Landfall | Summary
Posting Date: February 2, 2011, 10:00:00 AM

The western eyewall of Severe Tropical Cyclone Yasi began crossing the stretch of coast between Innisfail and Cardwell at midnight Wednesday local time, bringing intense winds and battering waves. The storm made the expected southwestward turn in the hours prior to landfall, sparing Cairns, a city of over 150,000, from significant damage. The storm strengthened on Wednesday to Category 5 on the Australian cyclone scale, which translates to a strong Category 4 on the Saffir-Simpson scale. According to the 3:00 AM AEST advisory from the Australia Bureau of Meteorology (BOM), Yasi was located 140 km south-southwest of Cairns and 95 km southwest of Innisfail, moving west-southwest at 33 km/h. Maximum winds gusts at landfall were are 290 km/h, but have since decreased to 260 km/h. The central pressure of the storm has increased over the past 6 to 12 hours and is currently at 941 mb, indicating that the storm is weakening from its interaction with land. Yasi remains a large, asymmetric storm, with damaging winds extending outward 450 km on the east side and 250 km on the west. Yasi is expected to continue to weaken rapidly as it begins to interact with the coastal Great Dividing Range. Thus, extensive wind damage should be restricted to the coastal areas and windward facing regions of the mountains. Prior to Yasi’s arrival, tens of thousands of residents were evacuated from the path of the storm, nearly 11,000 of them to some 20 evacuation centers along the coast. More than 89,000 homes have already lost electricity, and the prime minster Anna Bligh warns that much of Queensland, even in areas not affected by the storm, could lose power as well, possibly for several days. There are reports of widespread and severe roof damage, breakage of windows, and downed trees and power lines. At the time of landfall, the BOM warned of extremely dangerous storm surge along the 600 km of coast between Cairns and Prosperine until at least the morning high tide. A surge height of 3.0 meters was recorded at Clump Point (near landfall) and as high as 2.5 meters in Townsville. Higher surges in other locations are likely, with the potential to penetrate significantly inland. Yasi’s relatively fast forward speed should limit heavy rainfall accumulation. NASA’s Tropical Rainfall Measuring Mission (TRMM) satellites show up to 250 mm of precipitation in the wake of the storm. Coastal stations have all received less than 125 mm, and some higher elevation locations have received near 250 mm. Because the cyclone is hitting 500-1000 km north of the region worst-hit by flooding last month, Yasi’s inland flooding effect is expected to be minimal. Residences constructed after 1975 were designed for wind speeds of 250 km/h in building codes, while homes built after 2002 had design speeds of 265 km/h. Based on experience from recent storms, building code enforcement has been found to be quite stringent, but there is no prior experience to indicate how buildings will respond to Yasi’s forecast wind speeds. Uplift forces are expected to damage or remove many roof structures, and some older homes are likely to experience significant structural damage, even collapse. Steel-reinforced commercial buildings and high rises are not expected to experience significant structural damage, but wind-blown debris can damage windows and cladding. While refineries and mines are not expected to be severely damaged, zinc and coal operations have been slowed or halted in advance of the storm’s arrival, and railway transport systems have been shut down. Extensive losses are expected to agriculture, as Yasi is expected to hit Australia’s main production region for sugarcane and banana crops. Global commodity prices are reflecting these disruptions. Infrastructure damage, including to roads and power and communication networks, is expected to be severe. The Bureau of Meteorology stated that the “impact is likely to be more life threatening than any experienced during recent generations.” Cyclone Larry, a much smaller storm and less intense, struck Queensland in 2006 with Category 4 wind speeds, damaging 10,000 homes and causing more than 1 billion AUD in economic losses. In 1974, Cyclone Tracy, an exceptionally compact storm with gusts of up to 240 km/h, devastated the city of Darwin on the coast of Australia’s Northern Territory, destroying 70% of the city’s buildings and causing an estimated 800 million AUD (1974 dollars) of damage. The last storm to make landfall in Australia at Category 5 was in 1918. The AIR tropical cyclone team is currently analyzing the event using the latest available meteorological information and the AIR Cyclone Model for Australia. ALERT subscribers will be notified when loss estimates and event sets become available.

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Posting Date: February 2, 2011, 10:00:00 AM