The El Niño-Southern Oscillation (ENSO) significantly impacts global weather, with strong El Niño events often linked to prolonged dry conditions in Southeast Asia. While several high-impact El Niño events have coincided with prolonged dry conditions, leading to droughts, the underlying causal mechanisms remain complex and incompletely understood. In this study, we develop a minimal, data-driven model to quantify the conditions under which ENSO events amplify prolonged dry conditions risk in Southeast Asia. Unlike correlation-based approaches, our model identifies thresholds in sea surface temperatures and atmospheric water vapour content that increase the probability of prolonged dry conditions. Our results show that when ENSO-induced anomalies exceed specific temperature and atmospheric thresholds, prolonged dry conditions probability rises significantly, aligning with observed historical droughts. Additionally, the model reveals periods where this link weakens due to competing regional climate factors, suggesting that certain conditions mitigate the typical ENSO-prolonged dry conditions connection. These findings provide a more nuanced understanding of ENSO-driven prolonged dry conditions variability, offering a probabilistic predictive framework with potential applications in climate adaptation, agricultural planning, and regional resource management.