Multi‐Scale Interactions Associated With Two Offshore Rainfall Events Near the West Coast of Sumatra

Abstract This study investigates the offshore propagation of precipitation off the west coast of Sumatra on February 1 and 4, 2018, focusing on specific events to complement previous studies on seasonality. We use ERA5, MERRA–2, IMERG, Padang radar data, and cloud‐permitting scale simulations with WRF‐ARW V4.1.3 to understand the roles of the land breeze, gravity waves, and convective outflow in these two events. On February 1, convection organizes north of Padang and propagates approximately 100 km offshore. On February 4, a multicellular system organizes south of Padang and travels over 150 km offshore. Large‐scale environmental conditions reveal stronger westerly winds from the Indian Ocean on February 1 and strong northeasterly winds from the South China Sea on February 4. Both events occur in regions with high surface humidity and weak 900 mb winds along the coastline. WRF simulations show that on February 1, the sea breeze uniformly transitions to a land breeze, while on February 4, it forms chaotically. Convective outflow enhances offshore precipitation by interacting with the land breeze, creating additional convergence zones and intensifying convection. Gravity waves played a minor role, contributing to atmospheric instability. The results of this study conclude that offshore‐moving convection is primarily driven by the land breeze and convective outflow, with gravity waves playing a minor role. The land breeze initiates convection, while the convective outflow enhances and sustains offshore propagation by creating additional convergence zones and intensifying convection. Moisture advection precedes nocturnal propagation, increasing atmospheric instability and creating favorable conditions for nighttime offshore precipitation.