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SummaryThe mean monthly and annual rainfall series for 30x30 blocks in the eastern Transvaal-Swaziland region ara analyzed. These series show temporal and spatial characteristics in the regional precipitation regime. Significance is attributed to oscillatory forcings with quasi-periodicities of about 16-20 years and 13-14 months that operate throughout the area. Oscillations near the quasi-biennial cycle are also observed but with less significance. Principal component analysis provides a number of eigenvectors which are identified with changes in the seasonal characteristics of the regional rainfall. The annual cycle clearly dominates over the entire region with January (mid-summer) being the wettest month. The second eigenvector has pronounced loadings in the spring/early summer (November) period and clear spatial responses that are attributed to topographically induced differences in the deep convective processes of the area. Higher principal components are not as clearly defined in their temporal structure. The third eigenvector, however, is attributed partially to synoptic scale forcings which produce different rainfall characteristics over the coastal plains relative to the high inland plateau.

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