Tropical Cyclones Affecting Geraldton

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Tropical Cyclones Affecting Geraldton

It is estimated that a cyclone impact causing wind gusts in excess of 90 km/h in the vicinity of Geraldton occurs about once every six to eight years on average. This is considerably less than that for communities along the Pilbara coast reflecting the decreased risk southwards along the west coast. However, the frequency is not evenly distributed. Apart from the indirect impact of Herbie in 1988 the last cyclone to cause gales at Geraldton was Hazel in 1979. However, Hazel was preceded by Alby (1978), Wally (1976) and Beverley (1975) in the previous four years.

In general, cyclones weaken as the move southwards over cooler water and to latitudes where the atmospheric winds are unfavourable for cyclones. Indeed, winds speeds over 170 km/h have never been recorded south of Carnarvon. Although losing their tropical cyclone characteristics these systems may move at speeds in excess of 60 km/h. As they accelerate the structure of the storms changes so that the regions of heavy rains and strong winds are displaced on different sides. The co-location of warm squally winds without rain on the left side (when looking along the direction of the track) causes conditions highly favourable to severe duststorms and the spread of fires. The dust storms and fires associated with the 1937 cyclone and again with Alby typify this dangerous weather scenario. Heavy rainfall is more likely on the southern side of the cyclone. As a result the type of impact is highly dependent on the track of the cyclone (see schematic of a cyclone undergoing extra-tropical transition).

Although the inadequacy of early wind records makes it difficult to compare events, the most significant impacts to the Geraldton district have been in 1872, 1915, 1937 and 1956.

Cyclones have occurred near Geraldton from January to April although they are most frequent in March as shown in figure 2. Cyclone Herbie occurred in May but only the indirect impact of flooding affected the area.

Tracks

Cyclones that impact Geraldton typically form over warm ocean waters to the north of the state. The typical steering of these systems is to the southwest and then to the south and southsoutheast as they move further south as shown in figure 1. The notable exceptions are Alby (1978) and Herbie (1988) that moved in from the Indian Ocean. While Herbie's main impact was at Shark Bay, it also caused considerable flooding in the Geraldton district. Alby's path was well away from Geraldton however it was responsible for causing gales across southwestern parts of the state.

See also the Interactive Tropical Cyclone Plotting web page to access tracks of historical tropical cyclones.

Figure 1. Tracks of notable cyclones affecting Geraldton. Click on image to enlarge.

Figure 2. Monthly occurrence of cyclones affecting Geraldton. Click on image to enlarge.

Flooding

Although located on the Chapman River, Geraldton is not prone to major flooding. Localised flash-flooding is certainly possible near the river and in other susceptible low-lying areas. However, the Irwin and Greenough Rivers have larger catchment areas and pose a greater threat to Dongara and to built up areas near the Greenough River. Cyclone Herbie in 1988 caused rapid rises in these rivers inundating low-lying areas.

Some Notable Cyclones Impacting Geraldton

Tropical Cyclone Wind Gust (km/h) Impact Description
20 Feb. 1872- A cyclone, described as being of unprecedented severity caused considerable damage in Geraldton and also at Dongara where the Church was the only building unscathed. Marine Terrace was entirely submerged. The Geraldton jetty was very badly damaged.
25 Feb 1915- Winds caused extensive minor roofing damage in Geraldton, felled hundreds of trees in Greenough and brought down windmills throughout the district. Heavy rains flooded Geraldton's main street, washed away the Geraldton - Northampton railway line in a number of places and flooded Northampton carrying away the parapets of the stone bridge.
18-20 Feb. 1921- Four fishing boats wrecked at Geraldton while many others were damaged at Dongara and on Abrolhos Islands where one man drowned. The old Gwalia Church collapsed at Northampton.
9 Feb 1937130 est. Damage was widespread in the district. About 13 km of telephone line was blown down between Geraldton and Greenough. The breakwater was damaged and the railway approaches to the wharf were undetermined by the sea. Two men were struck by flying corrugated iron. Signs, fences and verandahs were blown down and small boats damaged. Significant damage was also reported from Mullewa and Yuna.
3-4 Mar. 1956140

Shipping was battered in Geraldton Harbour overnight. The grain freighter Cape St. David was smashed against her berth and her hull badly damaged and some boats were left high and dry 80 m from the water line. Damage along the water front was estimated at 200,000 pounds. In the town, trees were uprooted and buildings damaged by the wind and rain. A man was injured by a sheet of corrugated iron.

At Abrolhos Island, three cray boats sank and three jetties were swept away, along with huts and stores.

Wally, 27 Feb. 1975108 Wind speed exceeded gale force at Geraldton, Northampton, Kalbarri and Dongara where the eye passed over at 7:30 am, but damage was of a minor nature.
Alby, 3-4 April. 1978109 Widespread dust storms caused soil erosion and some minor damage was reported, but the impact was not as great as in Perth and the southwest.
Hazel, 14 Mar. 1979117 Hazel travelled down the west coast passing over Kalbarri and Geraldton where the pressure fell to 977 hPa. Considerable damage occurred to buildings, trees, pasture and stock feed in the northern agricultural area especially around Geraldton.
Herbie, 21 May 1988- Although passing near Shark Bay, Herbie caused heavy rain to the south that flooded the Irwin and Greenough Rivers, inundating Dongara.