Debbie formed on 18 December in the Arafura Sea, within 250 kilometres of the northern Australian coast. Debbie tracked southwest, intensifying to severe tropical cyclone strength early on 20 December. During the afternoon of 20 December, Debbie shifted to a more southerly track, began to weaken slightly and then crossed the Northern Territory coast in the evening between Goulburn Island and Maningrida. Debbie continued to move south over land, decaying into a rain depression on the morning of 21 December and continuing south-westwards over land for the next few days.
A tropical low formed within the monsoon trough on 16 December, as an MJO pulse propagated into the region. Under the influence of a low to mid-level easterly air-stream the low moved slowly west. A deep easterly surge, combined with decreasing upper-level shear, created favourable conditions for the low to slowly develop while continuing westward. On 18 December the low slowed and began moving to the southwest, as it came under the increasing influence of the monsoonal westerlies. Debbie reached cyclone intensity on 18 December and continued tracking to the southwest. Just prior to landfall, Debbie began to weaken as a result of restricted upper outflow. Debbie also came under the influence of some weak vertical wind shear, and sustained possible entrainment of dry air before landfall. During the evening of 20 December Debbie crossed the northern Australian coast and weakened to a rain depression early on 21 December.
As Debbie crossed a sparsely populated section of the coast, no significant structural damage occurred to townships. The communities of Warruwi (on Goulburn Island) and Maningrida suffered some minor structural damage such as lifted sheets of roofing iron. Warruwi sustained tree damage to power lines, with interruptions to both power and water supplies following Debbie 's landfall. The region exposed to Debbie 's core sustained severe vegetation damage, with 30-40 per cent of trees felled in the area. As the rain depression tracked southwest over the Northern Territory Top End and finally into the Kimberley region of Western Australia, heavy rainfall caused significant rises in river levels with localised flooding in many areas. Charles Point, near Darwin, received 197 mm on 22 December, while Tindal, near Katherine, received 284 mm on 23 December. Roads were cut at the Cullen and Waterhouse rivers due to flooding.
Track and intensity
All times in UTC - add 9.5 hours to convert to CST.