Understanding Recent and Near-term Future Changes in Australian Tropical Cyclones

The short historical record of tropical cyclones (TCs) combined with the rarity of occurrences in any given location makes it challenging to evaluate past changes in TC impacts, and to predict future changes. Analysis of Australian cyclones are limited by both the short observing record and the fact that a number of changes has occurred in observing practices. Despite the short record, significant changes have already been observed. The number of strong TCs has increased and the storm lifetime peak intensity has migrated southward. If this southward shift continues cities along Eastern and Western Australian coasts could experience tropical TCs more often than in the past, with extratropical transitioning storms also extending their impacts to higher latitudes. Statistical modeling gets around the rarity of occurrence, but these models are commonly based on past storm tracks, and therefore largely ignore recent and near-term future changes in storm tracks.

For this study, the NCAR CESM Decadal Prediction Large Ensemble Project (DPLE) dataset is used to explore how TC activity has changed in the recent climate, and how they are predicted to change in the next 5 to 10 years. The DPLE comprises 40-member ensembles initialized every year from 1954 to 2017. Each prediction extends out 10 years resulting in 25000 years of model data spanning past, current, and near future climates. TC-like vortices are tracked in the predictions using an automated tracking algorithm. Using these tracked TCs, we investigate how cyclones have changed along the Australian South East coast from Southeast Queensland to the northern parts of New South Wales in recent climate, and what the projected changes are for the next decade.