Want to know how a storm is put into it's category? Well here is what makes a storm a Tropical Depression, Tropical Storm, or the different categories of a Hurricane. It's called the Saffir-Simpson Hurricane Wind Scale.
Tropical Depression: A storm is a Tropical Depression when it has wind speeds of <38mph
Tropical Storm: A Tropical Depression can be upgraded into a Tropical Storm when the wind speeds are 39-73mph
Once the winds go past 73 you get a Hurricane.
Cat. 1: Wind speeds of 74-95mph
Cat. 2: Wind speeds of 96-110mph
Cat. 3: Wind speeds of 111-129mph
Cat. 4: Wind speeds of 130-156mph
Cat. 5: Wind speeds that are greater or equal to 157mph.
Then there is Post-Tropical Cyclone. That is when the Tropical Storm, Depression or Hurricane not longer the characteristics of the category it was last. It can continue to release heavy rainfall. There are two classes to a Post-Tropical Cyclone: Extratropical ( A storm of any category where the main energy source is a mixture of warm and cold air masses ) and remnant low ( A storm that no longer has a convective organization to it and it's wind speed is lower that 34 knots ( 38 mph ) .
Tropical Depression: A storm is a Tropical Depression when it has wind speeds of <38mph
Tropical Storm: A Tropical Depression can be upgraded into a Tropical Storm when the wind speeds are 39-73mph
Once the winds go past 73 you get a Hurricane.
Cat. 1: Wind speeds of 74-95mph
Cat. 2: Wind speeds of 96-110mph
Cat. 3: Wind speeds of 111-129mph
Cat. 4: Wind speeds of 130-156mph
Cat. 5: Wind speeds that are greater or equal to 157mph.
Then there is Post-Tropical Cyclone. That is when the Tropical Storm, Depression or Hurricane not longer the characteristics of the category it was last. It can continue to release heavy rainfall. There are two classes to a Post-Tropical Cyclone: Extratropical ( A storm of any category where the main energy source is a mixture of warm and cold air masses ) and remnant low ( A storm that no longer has a convective organization to it and it's wind speed is lower that 34 knots ( 38 mph ) .