Storm Surge is an abnormal rise of water generated solely by a storm, over and above the predicted astronomical tide. Storm surge occurs where winds are blowing onshore, especially during a tropical storm or hurricane event, and water can no longer go down so it goes up and inland.
The distance to the closest body of water subject to storm surge is asked because these areas will likely see the most severe damages during a coastal flooding event.
The most common water source for storm surges are the Atlantic Ocean, the Pacific Ocean, Gulf of Mexico, bays and inlets connected to these bodies of water, and large lakes and rivers that are susceptible to tidal movement.
Source: NOAA. National Ocean Service website, https://oceanservice.noaa.gov/facts/stormsurge-stormtide.html