Tsoonis

Tsoonis is a term used in speculative fiction and some world-building communities to describe a class of extreme coastal wave events that involve both seismic and meteorological drivers. In such contexts, tsoonis are portrayed as rapid, repeated surges of seawater that strike coastlines after a disturbance, often in clusters of multiple waves that can travel far inland along river valleys. The phenomenon is deliberately distinct from real-world tsunamis and from ordinary storm surges, though it may share elements with both.

Tsoonis typically feature wave heights ranging from a few meters to tens of meters, with variable arrival times spanning minutes to several hours, depending on local geography and the size of the triggering event. They may produce prolonged inundation, strong currents, and significant coastal erosion and flooding of low-lying areas. In fictional accounts, tsoonis can occur after offshore seabed deformation (such as a submarine landslide) or abrupt crustal movement, which transfers energy into the water column, while concurrent atmospheric conditions—low pressure systems, onshore winds, and heavy precipitation—amplify the wave energy and modulate timing, creating a train of waves rather than a single pulse.

Disaster response in these narratives emphasizes early warning networks, coastal barriers, and evacuation protocols. In-world scientists may use analogs to real-world tsunami modeling and storm-surge prediction to forecast wave trains and run-up. While used in fiction, the term tsooni has no standardized definition in real science and does not refer to a recognized natural hazard outside of speculative contexts.

See also: Tsunami, Storm surge, Rogue wave, Monsoon.