In the two days before it hit Florida, Hurricane Helene grew from a relatively weak tropical storm into a major Category 4 hurricane.
When a storm gets powerful very quickly like that, scientists call it rapid intensification. Such rapid intensification is relatively normal for major hurricanes that form in the Atlantic, according to federal hurricane data. For example, every Category 5 hurricane that hit the United States in the last century was a tropical storm three days earlier, according to Ken Graham, the director of the National Weather Service.