Summary
Orson was one of the most severe of all documented cyclones in the Australian region and, at its most intense, the central pressure of 905 hPa was the lowest on record for an Australian cyclone.
A low originally formed off Darwin on 17 April and moved to the west southwest through the Timor Sea reaching cyclone intensity during 18 April. Orson rapidly developed on 19-20 April and reached category 5 intensity late on 20 April. The centre of the cyclone passed just west of the North Rankin A gas platform just after midnight WST 23 April, where a pressure of 905 hPa and 249 km/h wind gusts (reduced to 10 m) level were recorded prior to the destruction of the anemometers by the cyclone. Orson maintained intensity until landfall west of Dampier, although fortunately this was near the time of low-tide. Orson gradually weakened as it moved over inland WA.
In all, Orson is estimated to have caused approximately US$16 million (1989 dollars) worth of damage (uninsured losses would be higher). Orson caused damage to 70 per cent of homes in Pannawonica. The damage included the partial destruction of the Bureau of Meteorology Weather Watch radar at Dampier which was being used to track the cyclone.
Observations:
North Rankin platform: minimum pressure 905 hPa (data courtesy of Woodside)
Mardie 211 km/h wind gust. Dampier 183 km/h wind gust.
For more details see the TC Orson Report (pdf) or the BoM TC Orson publication produced in 1992 (pdf)
Track and intensity
All times in WST - subtract 8 hours to convert to UTC.
