We used observational data to construct the precursory relationship between sea level anomalies (SLA) in the southeastern tropical Indian Ocean (SETIO) in boreal fall and Niño 3.4 sea surface temperature anomalies index one year later. The application of the above relation to the prediction of the 2020/2021 La Niña was a great success. The dynamics behind are the Indo-Pacific “oceanic channel” connection via the Indian Ocean Kelvin wave propagation through the Indonesian seas, with the atmospheric bridge playing a secondary role. The high predictability of La Niña across the spring barrier if a positive IOD should occur in the previous year suggests that the negative SETIO SLA in fall is a much better and longer predictor for this type of La Niña prediction than the WWV. In comparison, positive SETIO SLA lead either El Niño or La Niña by one year, the development of which is found to be dependent on the status of the MC. The combined effects of the ITF and WBC on the development of ENSO across the “spring barrier” suggesting importance of the oceanic channel in ENSO dynamics and predictability.