TC Billy began as a tropical low to the north of Port Hedland. It reached cyclone intensity on 2 December 1999 and moved on a southwest track towards the west Pilbara coastline. Its structure improved significantly on 3 December, with morning visible satellite images on 4 December showing an eye pattern for a few hours. As the cyclone moved further to the southwest very rapid shearing occurred overnight on 4 December. It weakened to below cyclone strength near Barrow Island and eventually crossed the coast near Onslow as a tropical low.
For more details see the TC Billy Report (pdf)
Track and intensity
All times in WST - subtract 8 hours to convert to UTC.