Tropical cyclones are rapidly rotating storm systems characterized by thunderstorms and strong winds circulating around a low-pressure center, often referred to as the “eye.” These systems are also known by other names, including tropical depressions, tropical storms, and hurricanes, depending on their intensity.Â
- June 13, 2025
Hurricane Season Basics: Understanding Tropical Cyclones
What are Tropical Cyclones?
Tropical cyclones are rapidly rotating storm systems characterized by thunderstorms and strong winds circulating around a low-pressure center, often referred to as the “eye.” These systems are also known by other names, including tropical depressions, tropical storms, and hurricanes, depending on their intensity.Â
Conditions for Formation
For a tropical system to form and strengthen, several key atmospheric and oceanic conditions must align:
- Warm Ocean Waters: The water temperature needs to be at least 80°F.
- Unstable, Moist Atmosphere: A favorable environment requires an atmosphere that is both unstable and rich in moisture.
- Pre-existing Disturbance: There must be an initial disturbance or area of thunderstorm activity to act as a starting point.
- Low Vertical Wind Shear: This refers to minimal change in wind direction and speed at different elevations in the atmosphere. Low wind shear is crucial for the storm to organize and intensify.
Classifying Tropical Cyclones by Wind Speed
Once a tropical system develops, its classification is determined by its highest sustained wind speed, measured directly or estimated from satellite data.Â
- Tropical Depression: A tropical cyclone with maximum 1-minute sustained surface winds of 33 knots (38 mph) or less.
- Tropical Storm: A tropical cyclone with maximum 1-minute sustained surface winds ranging from 34 to 63 knots (39 to 73 mph).
- Hurricane: A tropical cyclone in the Atlantic, Caribbean Sea, Gulf of Mexico, or eastern Pacific with maximum 1-minute sustained surface wind of 64 knots (74 mph) or greater.
- Major Hurricane: A hurricane that reaches Category 3 or higher on the Saffir/Simpson Hurricane Scale, with sustained winds greater than 110 mph.
The Saffir-Simpson Hurricane Wind Scale (SSHWS)
The Saffir-Simpson Hurricane Wind Scale (SSHWS) is a tool that categorizes hurricanes based solely on their wind speed to determine their intensity. It’s an updated version of the original scale developed by Herb Saffir and Bob Simpson.Â
|
Category
|
Wind Speeds
|
Damage
|
|---|---|---|
|
1
|
74 - 95 mph
|
Very dangerous winds will produce some damage
|
|
2
|
96 - 110 mph
|
Extremely dangerous winds will cause extensive damage
|
|
3
|
111 - 130 mph
|
Devastating damage will occur
|
|
4
|
131 - 155 mph
|
Catastrophic damage will occur
|
|
5
|
For a more detailed table, you can visit the National Hurricane Center’s website.Â
When is Hurricane Season?
Hurricane season officially runs from June 1st through November 30th. However, it’s important to note that storm systems can occasionally organize outside of this period. For example, one of the earliest hurricanes on record formed in 1938, reaching hurricane status on January 3rd. Similarly, Hurricane Alice formed in December 1954 and maintained its intensity until January 6, 1955.Â