In December 2023, the coastal town of Kayalpattinam in Tamil Nadu recorded an extraordinary rainfall exceeding 950 mm on December 17 and 18, resulting in severe flash floods and devastation to livelihoods in the community. This study critically examines the physical mechanisms driving this event across scales. Employing regional reanalysis datasets, we elucidate the localized characteristics responsible for extreme precipitation and systematically address the associated uncertainties. The investigation revealed that the spatiotemporal dynamics of moisture transport played a vital role in the increased moisture influx over the region. In particular, the local convection combined with heightened atmospheric instability and intensified advection in the surrounding areas played a pivotal role in the formation of significant mid-tropospheric cyclones. These developed atmospheric phenomena are rarely observed in this region, which typically experiences tropical cyclones and depressions more frequently. This emphasizes the necessity of conducting meticulous investigations to improve risk assessments and preparedness for future climatological phenomena of similar magnitude.