Tropical Cyclones Affecting Geraldton

Tracks | Flooding | Notable TCs | TC Herbie

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