Extreme El Niño events development depends not only on equatorial Pacific heat recharge but also on the efficiency with which recharge anomalies are converted into coupled ocean–atmosphere growth. Using ocean reanalysis data, we investigate how the Indo-Pacific pressure-head state—a physically based proxy for the Indonesian Throughflow (ITF) and associated interbasin ocean-memory background—modulates ENSO recharge efficiency. Historical analyses show that similar recharge magnitudes can produce markedly different ENSO outcomes depending on the evolution of the Indo-Pacific pressure-head state and the associated recharge efficiency. Negative pressure-head states, associated with a weakened ITF, favor more efficient conversion of recharge anomalies into sea-surface temperature growth and equatorial zonal-wind feedbacks, whereas positive pressure-head states, associated with a strengthened ITF, suppress the development of coupled feedbacks. The potential 2026/27 El Niño exhibits strong equatorial recharge, comparable to that preceding previous super El Niño events, but is accompanied by a distinct evolution of the Indo-Pacific pressure-head state. Atmospheric coupling during early 2026 remained weaker than during the rapid growth phases of the 1997/98 and 2015/16 events, whereas the subsequent transition toward negative pressure-head conditions coincided with accelerated SST growth. These results suggest that the Indo-Pacific background state primarily modulates the timing and efficiency of coupled ENSO growth rather than acting as a deterministic controller of the final event amplitude.
 

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