Monthly rainfall data for the state of Victoria in south-eastern Australia were analyzed using principal component analysis and Varimax orthogonal rotation, with the intention of revealing typical patterns of rainfall variability. Two data sets were used: a spatially detailed set for 1970–1980, and a less spatially detailed set for 1905–1980. The first five rotated principal component patterns (RPCPs) produced from the two data sets showed the same structure. These five RPCPs each dominated rainfall over a particular sub-region of the study region, and the climatic regionalization that this suggested appeared to be one strongly determined by topography.
The anomalies of Australian region mean monthly mean sea-level (MSL) pressure associated with these five RPCPs of rainfall were determined using correlational techniques. Of the five main RPCPs of rainfall, the pattern based in the south-west of the state showed the strongest relationship with monthly pressure anomalies, and was associated with the occurrence of onshore westerly winds. The results for the rainfall pattern based in northern Victoria were perhaps the most interesting. Rainfall in this region was related to the occurrence of anomalous northerly winds through southeastern Australia, although through the cooler months of the year these winds accompanied a low pressure anomaly centred over central Australia, whereas in the warmer months they were associated with a high pressure anomaly centred to the south-east of the continent. This northern rainfall pattern also showed some month to month persistence, and a distinct correlation with the Southern Oscillation.