The Okubo–Weiss–Zeta (OWZ) tropical cyclone (TC) detection scheme, which has been used to detect TCs in climate, seasonal prediction, and weather forecast models, is assessed on its ability to produce a realistic TC track climatology in the ERA-Interim product over the 25-yr period 1989 to 2013. The analysis focuses on TCs that achieve gale-force (17 m s−1) sustained winds. Objective criteria were established to define TC tracks once they reach gale force for both observed and detected TCs. A lack of consistency between storm tracks preceding this level of intensity led these track segments to be removed from the analysis. A subtropical jet (STJ) diagnostic is used to terminate transitioning TCs and is found to be preferable to a fixed latitude cutoff point. TC tracks were analyzed across seven TC basins, using a probabilistic clustering technique that is based on regression mixture models. The technique grouped TC tracks together based on their geographical location and shape of trajectory in five separate “cluster regions” around the globe. A mean trajectory was then regressed for each cluster that showed good agreement between the detected and observed tracks. Other track measures such as interannual TC days and translational speeds were also replicated to a satisfactory level, with TC days showing limited sensitivity to different latitude cutoff points. Successful validation in reanalysis data allows this model- and grid-resolution-independent TC tracking scheme to be applied to climate models with confidence in its ability to identify TC tracks in coarse-resolution climate models.

Tropical cyclones (TCs) can have severe impacts on Australia. These include extreme rainfall and winds, and coastal hazards such as destructive waves, storm surges, estuarine flooding, and coastal erosion. Various aspects of TCs in the Australian region have been documented over the past several decades. In recent years, increasing emphasis has been placed on human‐induced climate change effects on TCs in the Australian region and elsewhere around the globe. However, large natural variability and the lack of consistent long‐term TC observations have often complicated the detection and attribution of TC trends. Efforts have been made to improve TC records for Australia over the past decades, but it is still unclear whether such records are sufficient to provide better understanding of the impacts of natural climate variability and climate change. It is important to note that the damage costs associated with tropical cyclones in Australia have increased in recent decades and will continue to increase due to growing coastal settlement and infrastructure development. Therefore, it is critical that any coastal infrastructure planning and engineering decisions, as well as disaster management decisions, strongly consider future risks from tropical cyclones. A better understanding of tropical cyclones in a changing climate will provide key insights that can help mitigate impacts of tropical cyclones on vulnerable communities. An objective assessment of the Australian TCs at regional scale and its link with climate variability and change using improved and up‐to‐date data records is more imperative now than before. This article is categorized under: Paleoclimates and Current Trends > Modern Climate Change

A recently validated technique for detecting and tracking tropical cyclones (TCs) in coarse resolution climate models was applied to a selected group of 12 models from the Coupled Model Intercomparison Project (CMIP5) to assess potential changes in TC track characteristics in the Southern Hemisphere (SH) due to greenhouse warming. Current-climate simulations over the period 1970-2000 were first evaluated against observations using measures of TC genesis location and frequency, as well as track trajectory and lifetime, in seven objectively defined genesis regions. The 12-model (12-M) ensemble showed substantial skill in reproducing realistic TC climatology over the evaluation period. To address potential biases associated with model interdependency the analysis was repeated with an ensemble of five independent models (5-M). Results from both the 12-M and 5-M models were very similar, instilling confidence in the models for climate projections. Projected changes in TC track density between the current-and future-climate (2070-2100) simulations under the Representatives Concentration 8.5 Pathways (RCP8.5) were also assessed. Overall, projection results showed a substantial decrease (~1-3 per decade) in track density over most parts of the SH by the end of the twenty-first-century. This decrease was attributed to a significant reduction in TC numbers (~15-42%) consistent with changes in large-scale environmental parameters such as relative vorticity, environmental vertical wind shear and relative humidity. This study has important implications for regional-scale climate change and adaptation pathways for the vulnerable regions in the SH, particularly the small island countries in the Pacific.

The sensitivity of tropical cyclone (TC) projection results to different models and the detection and tracking scheme used is well established. In this study, future climate projections of TC activity in the North Indian Ocean (NIO) are assessed with a model-and basin-independent detection and tracking scheme. The scheme is applied to selected models from the coupled model intercomparison project phase 5 (CMIP5) experiments forced under the historical and representative concentration pathway 8.5 (RCP8.5) conditions. Most models underestimated the frequency of early season (April-June) TCs and contained genesis biases equatorward of~7.5 N in comparison to the historical records. TC tracks detected in reanalysis and model data were input to a clustering algorithm simultaneously, with two clusters in the Arabian Sea and two in the Bay of Bengal (k = 4). Projection results indicated a slight decrease of

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