ELI5: When does a tropical storm become a hurricane?

A tropical storm becomes a hurricane when its strongest steady winds reach 74 miles per hour or more.

• Think of it like a storm level-up: a tropical storm is a stronger, named storm, and when it gets even stronger, it becomes a hurricane.
• Before that, if the winds are below 39 mph, it is a tropical depression.
• From 39 to 73 mph, it is a tropical storm.
• At 74 mph or higher, it is called a hurricane.

• A tropical depression is like a kid learning to ride a bike.
• A tropical storm is like riding faster and wobbler, with a name on it.
• A hurricane is like the bike going very fast and becoming much more powerful.

So, the short answer is: when the wind speed passes 74 mph, a tropical storm becomes a hurricane.