Severe Tropical Cyclone Thelma was a tropical cyclone that affected northern Australia from 6 December 1998 until 12 December 1998. Cyclone Thelma was one of the most intense tropical cyclones to be observed off the coast of Australia. Thelma formed in the Arafura Sea north of the Northern Territory while intensifying rapidly into a Category 5 cyclone, passing very near the Tiwi Islands and posing a severe threat to Darwin, but passed by at a distance of 200 km (120 mi). It then moved across the Timor Sea before hitting the north Kimberley coast. Thelma was the first known Category 5 cyclone to be observed in the Timor Sea, and was also the most intense cyclone to threaten Darwin since Cyclone Tracy on Christmas Eve in 1974. Ten months after the storm's passage, the skull of an 81-year-old