[1] Within the Southern Hemisphere there are officially three areas where tropical cyclones develop on a regular basis: the South-West Indian Ocean between Africa and 90°E, the Australian region between 90°E and 160°E, and the South Pacific basin between 160°E and 120°W.
Within the basin, most tropical cyclones have their origins within the South Pacific convergence zone or within the Northern Australian monsoon trough, both of which form an extensive area of cloudiness and are dominant features of the season.
There is a history of tropical cyclones affecting northeastern Australia for over 5000 years; however, Clement Lindley Wragge was the first person to monitor and name them.
[2] In the early history of tropical cyclones in the Australian region, the only evidence of a storm was based on ship reports and observations from land.
In Western Australia in particular, the lack of population centers, shipping lanes, radars, and offshore stations meant that storms were tracked infrequently.
The region also covers waters off Indonesia that include the main islands of Java, Bali, Lombok, Sumbawa, Sumba, Flores and the western half of Timor.
[6] The sub-region covers waters off Western Australia north of Shark Bay, and extends westward to Christmas Island.