September 2016 harbored record-breaking three tropical cyclones (TCs) affecting Taiwan within a month. Multiple modulating processes governing these three TC events and associated rainfall and intensification features are examined. September 2016 fell in a La Niña phase. For interannual variability, major warm sea surface temperature (SST) anomalies in September 2016 shifted eastward toward the tropical western North Pacific (WNP) compared to the Maritime Continent during other La Niña events. These SST anomalies induced strong convergence and convection anomalies facilitating TC formation. The TCs formed in the joint region between a northern anticyclonic anomaly over the northern WNP and a southern cyclonic anomaly extending from the tropical WNP toward Taiwan. They were steered by anomalous easterly/southeasterly flows northwestward toward an anomalous cyclonic center overlying Taiwan, leading to intensive TC activity affecting Taiwan. For intraseasonal variability, the three TCs of September 2016 were steered by anomalous easterly/southeasterly flows in the southern section of a 30–60-day anomalous anticyclone over the subtropical WNP northwestward toward a 30–60-day anomalous cyclone that lay over Taiwan. During these events, local rainfall in Taiwan was mainly affected by moisture convergence due to 3–10-day transient anomalies, rather than intraseasonal anomalies. For TC intensification processes, faster intensification was assisted by decreases in vertical wind shear and increases in upward motion, moisture convergence, upper-level divergence, and SST. Intensification processes were mainly affected by transient anomalies. Overall, interannual and intraseasonal anomalies modulated TC genesis and movement, while transient anomalies influenced local rainfall and intensification processes.