Summary
Tropical cyclone Bobby was a large, intense cyclone that moved along the entire length of the northwest Australian coast, then inland over western and southern parts of Western Australia. A tropical low first developed on 19 February in the monsoon trough north of the Northern Territory coast. Initial development was retarded by strong easterly shear as the low moved steadily west-southwestwards north of a mid-level ridge axis. The zonal ridge pattern was disturbed by the approach of a large-amplitude frontal system during 21 and 22 February, decreasing wind shear over the system. Rapid cyclogenesis followed as deep convective cloud wrapped around the surface centre late on 21 February and Bobby was named early on 22 February near 16.1°S 120.8°E, about 500 km north of Port Hedland.
The cyclone continued to intensify during the next two days in an environment of decreasing shear as it moved south-southwestwards, closer to the mid-level ridge axis. Bobby reached hurricane intensity early on 23 February and peaked with estimated mean winds of 55 m/s (estimated central pressure 925 hPa) at 0900 UTC on 24 February, as it approached the Western Australian coast near Mardie (100 km west southwest of Karratha). A contraction of the radius of hurricane-force winds from 80 km to less than 30 km during this period of intensification was detected by a network of offshore automatic weather stations. However, the radius of gales remained unchanged at about 150 km which coincided approximately with the radius of central dense overcast cloud.
Bobby moved erratically for about 24 hours, executing several loops as it travelled along the coast. The cyclone crossed the coast near near Onslow around 1800 UTC on 25 February (between midnight and 0100. WST, where a maximum gust of 51 m/s and minimum pressure of 952 hPa were recorded. A storm surge of 1.3 m was recorded at King Bay about 30 km west of Karratha. The weakening cyclone maintained a southward overland track for another 24 hours then turned southeastwards and finally weakened into a rain-bearing depression over southern parts of Western Australia early on 27 February.
Eight people died during Bobby , seven in two fishing trawlers which foundered offshore from Onslow and one motorist who was drowned while attempting to cross a flooded creek near Carnarvon. Very heavy rain associated with the cyclone caused serious flooding over widespread areas throughout western and southern
Track and intensity
All times in WST - subtract 8 hours to convert to UTC.
