Tropical Cyclone Kelvin

Landfall | Summary
Posting Date: February 20, 2018, 4:30:00 PM

Tropical Cyclone Kelvin made landfall near Anna Plains Station, 250 kilometers (155 miles) south of Broome on the lightly populated Kimberley Coast of Western Australia, at about 7 a.m. on Sunday February 18, 2018, local time (23:00 UTC, February 17), with sustained winds of 148 km/h (92 mph). A red alert was issued across Western Australia as the storm impacted exposed coastal areas. As well as damaging winds, Kelvin delivered intense rainfall to the region, resulting in widespread flooding and road closures.

The intensity scale used by the Bureau of Meteorology in Australia (BoM) places tropical cyclones into five categories of increasing intensity. Tropical cyclones at Category 3 or above are considered severe tropical cyclones. At landfall BoM identified Tropical Cyclone Kelvin as a Category 2 storm. After landfall, however, Kelvin intensified and formed a distinct eye. This may prove to have been an example of the so-called “brown ocean effect,” where factors such as warm and wet soil combine with low surface friction to provide conditions conducive to cyclones intensifying over land. Such storms are known as landpfoons or agukabams in Australia. Kelvin has since weakened to below cyclone intensity.

Exposure at Risk

Australia’s cyclone season runs from mid-December to April, and peaks in February. Tropical cyclones tend to occur far more frequently near the northern half of the continent, and the lightly populated Kimberley and Pilbara coasts are impacted more than any other part of Australia. Because it experiences so many tropical cyclones, the area is well prepared to cope with them through stringent building codes and effective response plans. Australian building standards divide the country into four wind speed zones, of which region D—the most stringent—covers this small portion of the western coastline.

Residential buildings in Australia are mostly single-family homes, with primarily apartments and condominiums in larger cities. Most of Australia’s residential buildings are either wood frame or masonry, many with brick veneer. Most homes are low-rise, so wind damage tends to impact building envelopes (roofs and exterior walls).

The commercial and industrial building stock in Australia is predominantly concrete and steel. Large commercial buildings, especially mid-rise and high-rise structures, tend to be engineered and are therefore more resistant to wind damage than smaller buildings. Windows and cladding on engineered structures do risk impact damage from wind-borne debris, of course.

Agricultural buildings represent a wide variety of structures and tend to be similar in construction type to residential buildings. Most are low-rise, and masonry is commonly used although agricultural buildings are constructed with a wider range of materials than residential buildings. In many parts of Australia, agricultural buildings are generally not built to strict standards and are quite vulnerable to wind loads, particularly when light metal is used. Roofs are often made of wood or light metal and they tend to cover a large area and are therefore susceptible to large wind uplift forces.

With a combined population of about 25,000 Port Hedland and nearby South Hedland, some 220 miles west-southwest of Kelvin’s landfall, form the largest settlement in the region. In recent decades cattle and sheep farming have declined but offshore oil and gas resources have been developed. The area’s principal resource however, is iron ore, extracted from ranges inland by Australia’s largest mining companies, Rio Tinto, BHP, and Newcrest Mining. In terms of the tonnage of ore and other commodities it handles, Port Hedland is Australia’s busiest port.

Reported Impacts

Although wind damage to structures and trees has been reported, it is the intense rainfall that accompanied the storm that is responsible for its greatest impacts. Broome, for example, endured Tropical Cyclone Joyce in January and flooding soon after. Including totals from Kelvin it has received 1.5 meters of rainfall so far this year, more than ordinarily experienced in two years. Typical wind damage from a BoM Category 2 storm includes minor house damage; significant damage to signs, trees, and trailers; heavy damage to some crops; power failures; and the possibility of small craft breaking from moorings.

There are widespread road closures in the region because of flooding. A 660 km stretch of the Great Northern Highway—a key coastal artery—remains closed south and east of Broome, cutting off the town indefinitely. Lesser dirt and gravel roads are prone to being washed out, and many roads are still under repair following Tropical Cyclone Joyce. Stranded residents have been evacuated from the area, and supplies have been dropped by air to communities cut off by flooding.

Kelvin weakened below tropical cyclone intensity as it moved south across the region on Monday, but several flood warnings remain in effect for Western Australia, particularly for the Fortescue River, The Great Sandy Desert region, and the De Grey River. The system is predicted to have tracked to  the eastern Goldfields by Wednesday morning local time.

Landfall | Downloads
Posting Date: February 20, 2018, 4:30:00 PM

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