Cold SST anomalies develop over the southwestern Pacific and the southeastern Indian Ocean, crammed with the warm SST anomaly to the South of Australia, during positive SST-W4 events. In response, anomalous winds diverge from the colder region to the warmer oceanic region. This situation favors anomalous easterlies (westerlies) on the eastern (western) side of the continent. Along with the wind, moistures are transported to the Australian landmass. Moreover, the increase in specific humidity over the same region supports the enhanced rainfall over southeast Australia. Conversely, during negative SST-W4 years, the presence of warm SST anomalies over the western and eastern sides of Australia, packed with cold SST anomalies in the region to the south of Australia, reverses the atmospheric circulation. Consequently, the wind and moisture diverge, reducing the tropospheric specific humidity that leads to decreased rainfall over southeast Australia. 

During the positive phase, the oceanic region to the east (west) of South America experiences warmer (colder) SST accompanied by colder (warmer) SST in the southeastern subtropical Atlantic Ocean. As a result, wind advances from a colder to a warmer region and converges along with the moisture over South America. Hence, it enhances the specific humidity and favors above-average rainfall over the region. A similar (opposite) mechanism is observed in other regions that affect the decadal rainfall over Australia (South Africa). During the positive phase of the W4 pattern, the positive SST anomaly south of Australia, crammed with cold SST to the northeast of Australia, initiates a southerly wind to converge moisture over the land. As a result, the specific humidity increases and enhances the rainfall over the region. It can be noted that the divergent winds are southerly on a decadal scale instead of westerly/easterly on the inter-annual scale discussed earlier for the Australian rainfall. The SST gradient between nearby W4 SST anomaly patterns gives rise to easterly winds and converges the moisture toward the center of the subtropical Pacific Ocean. On the other hand, the western Indian Ocean has above-normal SST, forcing the wind offshore and diverging the moisture away from the land. Consequently, specific humidity decreases and results in below-normal rainfall over South Africa. This scenario is just the opposite during the negative phase. During the negative phase, the polarity of the SST W4 centers and related local atmospheric circulation anomalies reverse, causing a suppression (enhancement) in rainfall over South America and Australia (South Africa).