A review of historical tropical cyclone intensity in Northwestern Australia and implications for climate change trend analysis

Estimated tropical cyclone intensities for northwestern Australia over the period 1968/69 to 2000/01 obtained from a recent offshore oil and gas industry review are compared with the Bureau of Meteorology official tropical cyclone best track archive, a modified best track archive and another international reference data-set. Potential influences on the accuracy of estimating tropical cyclone intensity over time due to increasing technology, methodology, knowledge and skill are discussed. Historical Bureau of Meteorology practices in regard to estimating tropical cyclone intensity are also outlined and a method is described to potentially rectify the official track data archive to overcome some procedural issues. The methodology of the objective industry review process is then described, together with its expected limitations, and comparisons between the various data-sets are presented. It is shown that a bias towards lower intensities likely exists in earlier (mainly pre-1980) tropical cyclone central pressure deficit estimates of the order of at least 20 per cent in 1970, reducing to around ten per cent by 1980 and to five per cent by 1985. Inferred temporal trends in the estimated intensity from the original data-sets are therefore significantly reduced in the objectively reviewed data-set. Implications for detecting potential climate-change trends are discussed and recommendations are made for a detailed review of the tropical cyclone data-set for the entire Australian region as well as a call for improvements in the analysis and direct sensing of tropical cyclone intensity.