The average conditions of the Indonesian Throughflow (ITF) are well-represented by the top figure.
The transport varies significantly throughout the year. One main driver of the change in transport magnitude is the Monsoon. During the Indo-Australian Monsoon (November-February), westerly winds partly counteract the ITF transport, especially in the upper part of the water column. During the Southwest Monsoon (June-August), southeasterly winds over Indonesia drive additional flow through the ITF. In the transition months, downwelling favorable winds in the eastern Indian Ocean increase sea level in the southwest part of the ITF region, reducing the pressure gradient from the Pacific into the Indian Ocean and causing a minimum ITF transport. The sporadic eastward current in the Indian Ocean is referred to as the Wyrtki jet.
During times of reduced ITF transport, reversals of the ITF can occurred, especially in some of the smaller branches like the flow through Lombok Strait. The caused of these reversals is usually associated with specific weather systems. For example, Shinoda et al. (2012) showed an episode of flow reversal during May 2004. The development of a northward current anomaly can be seen in the sea surface height and current anomaly map.
Sea Surface Height (shading; m) and upper-ocean (average over 50–250-m depths) velocity (vectors) anomalies during 9–30 May 2004 relative to the mean of April–June 2004. Source Shinoda et al. (2012).