Interdecadal variability in Queensland tropical cyclone occurrence

Interannual and interdecadal variations in Australian region tropical cyclone formation are analysed using a new tropical cyclone data set compiled for the state of Queensland. Recent interannual correlations (since 1967) between the Southern Oscillation Index (SOI) and tropical cyclone formation in the Queensland region are good. Correlations for earlier periods are not good, particularly in the 1920s and 1930s. Data for storms that strike the coast are examined, under the assumption that these data will be more complete in the pre-satellite era than those for storms that stay out to sea. An upward trend in landfalling cyclone numbers before 1967, despite a slight downward trend in the SOI, suggests some missing storms in the early part of the record. However, the 1920s and 1930s are well known as periods when established SOI/rainfall relationships broke down in this region. It is possible that this may also have an effect on relationships between the SOI and tropical cyclones. Relationships of cyclone occurrence with an index of Pacific decadal variability are examined. There are clear differences in the number of tropical cyclones forming in this region between positive and negative phases of this index.