When does a tropical depression become a hurricane?

6 Storm Team Weather School

KNOXVILLE, Tenn. (WATE) — Tropical storm systems are best known as hurricanes, but that’s not the only form the storms can take. The storms begin as a tropical depression, then can strengthen into a tropical storm, then a hurricane, and possibly a major hurricane.

Tropical depression

When that circulation gets strong enough and the winds start picking and you have a center of circulation, it is called a tropical depression. Typically there are minimal impacts as the winds are generally less than 39 mph.

Tropical storm

Once wind speeds rise to about 40 mph, the tropical depression will become a tropical storm. Storms can be seen building across the center and overall it’s getting stronger. The winds range between 39 to 73 mph. These storms can cause some damage.


As the winds become stronger, a hurricane forms. The air near the center of the storm will be seen rising and an eye will potentially develop. Once an eye develops the storm is going to get much stronger. Hurricanes bring dangerous winds and extensive damage. Wind scales range from 1 to 5.

  • Category 1: Winds 74-95 mph
  • Category 2: Winds 96-110 mph
  • Category 3: Winds 111-129 mph (major)
  • Category 4: Winds 130-156 mph (major)
  • Category 5: Winds >156 mph (major)

Major hurricane

Hurricanes that reach Categories 3 to 5 are called major hurricanes. These are extremely powerful winds with sustained wind speeds of at least 115 mph. The damage from these storms can be catastrophic. In fact, Hurricane Katrina was a Category 5 and Hurricane Ida was a Category 4. Major hurricanes also have the ability to affect surrounding weather patterns.

Copyright 2021 Nexstar Media Inc. All rights reserved. This material may not be published, broadcast, rewritten, or redistributed.

Trending Stories

Latest News Videos

Fleet Services keeping Knoxville Fire Department engines running

Academy Sports donates $10,000 to Knoxville nonprofit

Green Magnet Academy receives donation for outdoor learning space

HonorAir flight delayed again

CNS employees suing for overtime pay

Teen pleads guilty in Tessa Majors murder