On double monsoon onset and its predictive signature

Abstract

The Indian monsoon is a complex phenomenon that greatly impacts agriculture and the economy of the region. Understanding the dynamics of the monsoon onset and its accurate predictions with a longer lead time is essential for effective planning and management decisions. Double monsoon onset is characterized by an early monsoon-like condition leading to a “bogus” (or false) onset followed by a delayed real onset. The present study provides an in-depth analysis of the 2023 monsoon onset, which was delayed 7 days than the normal monsoon onset, with a particular focus on understanding the predictive signature of such double monsoon onset. The study focuses on the total precipitable water vapour (TPW) to discern the monsoon onset over Kerala (MOK). Further investigation into the nature of the 2023 monsoon onset reveals the formation of Madden–Julian Oscillations (MJO) and twin perturbations, influencing convective activity and sea surface temperatures (SSTs). Notably, a distinct bi-peak evolution of surface winds is observed during the 2023 monsoon onset, suggesting a double monsoon onset pattern. Detailed analysis of 54 years of historical data spanning from 1950 to 2003 also suggests significant changes in wind speed over the Western Arabian Sea (WAS) for the cases of double monsoon onset. Accordingly, an index, namely the Double Monsoon Identification Index (DMII), is proposed to identify the potential cases of double monsoon onset. The DMII successfully predicted historical double monsoon onset cases (between 1950–2003) with an accuracy (ACC) of 0.96, a probability of detection (POD) of 0.9, and a false alarm rate (FAR) of 0.1 and identified two new cases between 2004–2023. The study highlights the predictive potential of surface winds in anticipating the double monsoon onset with considerable lead time from the climatological onset date, aiding proactive measures and planning in response to monsoon variability. © The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature 2025.