Hurricanes begin when the weather conditions are just right for a cluster of thunderstorms to form over a tropical ocean. If such a cluster remains long enough, it organizes into a tropical depression, with winds of up to 42 miles per hour. If a tropical depression increases to winds of 43 to 74 miles per hour, it is a tropical storm. A tropical storm is given a name and watched closely, by satellite, to see if it gets worse and begins to have the telltale circular shape of a hurricane. If the air pressure continues to drop, the wind rises to above 75 miles per hour, and a true hurricane is born.
Which of the following causes weather forecasters to say a storm has become a hurricane?
A cluster of thunderstorms form over a tropical ocean.
A cluster begins to organize into a tropical depression.
Winds increase to over 75 miles per hour.
Winds increase to 23 to 42 miles an hour.