Isaac is the chief meteorologist at the US Weather Bureau in Galveston at the time of the storm. The protagonist of the book, Isaac's experiences are the ones predominantly used by Larson to tell the story of the 1900 Galveston hurricane.

Born in 1861 in Eastern Tennessee, Isaac grows up on a farm in rural Monroe County. From an early age, Isaac is fascinated by meteorological phenomena: “Lightning was barely understood, tornadoes not at all. To a boy in a land of ghosts and wild men, how could they not be alluring?" (29). Isaac goes on to attend Tennessee's Hiwassee College, where he proves himself to be a polymath across several fields in both the sciences and humanities: “'I was not adept enough at prevarication to make a successful lawyer. I then made up my mind that I would seek some field where I could tell big stories and tell the truth.' He chose the weather" (29). By the time he graduates, Isaac is "a lean young man of middle height with angular features, lively dark eyes, and an expression of sobriety that made you want to tell him some awful joke just to see if he could laugh" (33).