An estuary is where salt water and fresh water meet. Estuaries are usually found at the edge of the coast, where the ocean water, or salty water, meets river, lake, any fresh water source, water.
A tributary is something completely different. It is a, usually smaller than the main river or lake, river/stream stemming off a bigger river or lake, or flowing into that river or lake.
Tornadoes form when warm, humid air collides with cold, dry air. The denser cold air is pushed over the warm air, usually producing thunderstorms. The warm air rises through the colder air, causing an updraft. The updraft will begin to rotate if winds vary sharply in speed or direction1
Great plains is the broad interior are of north america that used to be grasslands
Language seems the obvious answer
Answer; Hurricanes form when warm moist air over water begins to rise. The rising air is replaced by cooler air. This process continues to grow large clouds and thunderstorms. These thunderstorms continue to grow and begin to rotate thanks to earth's Coriolis Effect.