Although rainfall accounts for 25% of tropical cyclone-related fatalities in the United States, the threat of rainfall is somewhat underestimated in comparison to other hazards. Furthermore, rainfall is an interdisciplinary hazard, from the remaining unknowns in the underlying physics, to the effect on downstream hazards, and the difficulties associated with decision making. In terms of physical processes, rainfall is a complex mixture of drop creation, growth, and seeding by frozen hydrometeors, where the kinematic and thermodynamic environment determine the relative contributions of warm rain and ice phase microphysical processes and the ultimate particle trajectories. In addition, external influences such as vertical wind shear and topography can modify the azimuthal distribution of rainfall intensity and microphysical processes. After the rain reaches the ground, flooding, landslides, and river runoff are dangerous hazards that cause both fatalities and economic losses. Other indirect consequences of heavy rainfall, such as disruption of local transit networks, can negatively affect response and recovery efforts. Finally, forecast uncertainty due to model error, insufficient model resolution, and microphysical deficiencies make the communication of the rainfall threat challenging.

The proposed session would solicit abstracts on the aforementioned topics, with a specific interest in recent tropical cyclones (e.g., Hurricanes Harvey 2017, Florence 2018, Maria 2017, Lane 2018, Typhoon Mangkhut 2018, Tropical Cyclone Idai 2019). Ideally, the session would solicit abstracts on a variety of topics, including but not limited to: observational and modeling research, emergency management and decision-making studies, and forecasting successes and failures. We hope to take advantage of the diverse attendees to have a conversation about the complicated and interdisciplinary nature of tropical cyclone rainfall understanding, prediction, and mitigation.