Tropical Cyclone Joan

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8 - 9 December 1975

Summary

TC Joan was one of the most severe tropical cyclones to affect a Northwest town. Although the eye crossed the coast some 50 km west of Port Hedland, the city was subjected to sustained winds exceeding 90 km/h for about 10 hours with winds in excess of 120 km/h for three hours. The maximum measured wind gust was 208 km/h. Severe property damage occurred at Port Hedland and other settlements close to the cyclone's path. Subsequent flooding damaged roads and sections of the iron ore railways, particularly that of Hamersley Iron Pty Ltd. Sheep losses were heavy but, remarkably, no loss of human life or serious injury was reported. The estimated damage to private property and public facilities is believed to have exceeded $25 million.

Track and Intensity

Joan developed over the Timor sea and was named on 1 December. The system passed close to the northern tip of WA before moving on a west-southwest track over open waters gradually intensifying. Late on the 6th, Joan took an abrupt southerly turn eventually crossing the coast just 50 km west of Port Hedland at about 6am on the 8th.

Although Port Hedland recorded mean winds in excess of 90 km/h for about 10 hours, radar imagery suggested that the most destructive winds were in the range of 25 to 40 km of the centre, implying that Port Hedland winds were somewhat less than the maximum generated by Joan. The maximum wind gust was estimated to be about 250 to 260 km/h. The radius of gales was about 170 km.

The lowest recorded pressure at Port Hedland was 966 hPa, but a barometer at Mundabullangana homestead, about 6 or 7 km from Joan's track recorded a minimum pressure of 935 hPa about 1.5 hours after the eye of the the cyclone had crossed the coast when it was approximately 20 km inland. The central pressure of the system at the point of landfall was estimated to be around 925 hPa and the lowest pressure offshore about 915 hPa.

Figure 1. Track of TC Joan (click to enlarge).

Impact

Eighty-five per cent of all houses were damaged to some degree. In ocean front areas all houses were damaged and some unroofed. Beach sand was piled up to a depth of up to two metres. Power and communications were unavailable for several days. Total cost of repairs to buildings in Port Hedland estimated at $20 million, with $2.25 million needed on the destroyed hospital and $1 million on the Civic Centre.

A storm surge of at least 2.6 metres was estimated, however this occurred on lowering tides and no coastal inundation occurred. A much higher storm surge would have occurred to the west of Port Hedland closer to the crossing point. Had the storm surge peak coincided with high tide then the resulting water level would have been several metres above the highest astronomical tide.

Heavy rainfall inland caused very signficant flooding. Marandoo, near Tom Price registered 591 mm while many other sites recorded rainfall over 400 mm. The heavy rain occurred along and just east of the cyclone track. Some of the two and three-day totals registered over the Hamersley Range represent in excess of a once in 100 year event. Many tributaries of the Fortescue River such as the Weelumurra and Weeli Wolli Creeks overflowed causing flooding and washaways on the Mt Newman and Hamersley Iron railway lines. Serious flooding occurred on the Yule River. Repair costs to flood damage on roads and bridges after the passage of Joan was put at $1.5 million.

Figure 2. Four day rainfall totals: 7-11 December 1975.

Damage Photos

Photo 1. High tension power poles near Port Hedland airport.

Photo reproduced courtesy of The West Australian.

Photo 2. Part of the damage to the Hospital.

Photo reproduced courtesy of The West Australian.

Cyclone Parameters at the time of maximum intensity

Date/time: midnight 8 December 1975

Latitude: 19.5 °S

Longitude: 118.0 °E

Lowest estimated pressure: 915 hPa

Maximum estimated wind gust : 260 km/h