Characteristics of tropical cyclones in the Australian region

Characteristics of 500 tropical cyclones (TCs) in the Australian region and its three individual basins are examined based on 40 yr of satellite-supported observations. While tropical cyclones exhibit highly individual behaviors resulting in significant standard deviations, there are some systematic behaviors, which are documented. Most TCs in the Australian region originate from December to April. About 13 are observed each season, with half occurring in the western basin. Generally, the lifetime of a TC is about 71/2 days, during which time it covers over 2500 km at a mean speed of 15 km h(-1). Around half of the storms reach a maximum intensity corresponding to category 3 or higher (<970 hPa), as classified using a modified Saffir-Simpson scale. Tropical cyclones in the western and eastern basins have around 25% chance of making landfall, while those in the northern basin have an 80% chance. There appear to be preferred locations for TC genesis, close to the Australian coastline at around 120°, 135°, and 150°E. Genesis occurs near the mean position of the maximum low-level cyclonic vorticity and coincides with the monsoon trough from December to February, but occurs poleward of the trough in other months. The maximum intensity eventually achieved by TCs varies with genesis locations. For storms that reach category 3 or above, there are more corresponding origin points in the west than in both the gulf and the eastern basin. Recurvature generally follows attainment of maximum intensity, suggesting the importance of trough interactions on this behavior. The likelihood of extratropical transition of TCs, in the mean, increases to a peak in March, although there is variability across the three basins of the Australian region. Final dissipation has no preferred latitude, with many storms dissipating over the warm tropical oceans equatorward of 20°S.