In Twister, Helen Hunt plays a storm chaser named Jo Harding. The character’s first name is Jo, and she leads a team of researchers trying to deploy a device called Dorothy inside a tornado.
Jo is a meteorologist whose childhood trauma drives her fascination with tornadoes. As a young girl, she survived a tornado that killed her father. Years later, she works with her former husband, Bill Harding, to test Dorothy, a device designed to release sensors into a tornado and improve scientific understanding of these storms.
The names in the question can be confusing because Dorothy is the name of the research device, while Melissa is Bill’s fiancée and Bill is Jo’s former husband. Helen Hunt’s Jo is the film’s central storm-chasing figure, balancing scientific ambition with the personal danger of pursuing violent tornadoes. The 1996 film was directed by Jan de Bont and became a major disaster-film hit.