The difference between tropical storm types and how they’re defined

With hurricane season approaching, KPRC 2 Hurricane Headquarters is here to help Houstonians power through the storms by providing our audience with everything they need to know, starting with terminology.

[RELATED: Tropical disturbance could get hurricane season off to an early start]

Unsure if it’s a storm or disturbance, or don’t understand the difference either way?

Here’s how it breaks down:

A tropical cyclone with sustained surface winds from 39 mph (63 km/hr) to 73 mph (118 km/hr) is categorized as a tropical storm.

In September 2019, Tropical Storm Imelda caused major flooding throughout Houston, pouring more than two feet of water over some areas.

Before being upgraded to a storm, Imelda was categorized as a tropical depression.

A tropical depression is a tier below at lower speeds. Its maximum sustained surface winds up to 38 mph (62 km/hr).

Finally, a tropical disturbance is defined as a discrete tropical weather system of apparently organized thunderstorms. These storms are generally 100 - 300 nautical miles in diameter and originate in tropic or subtropic areas.

In June 2001, Tropical Storm Allison started as a disturbance in the Gulf of Mexico before making landfall in Houston.

A tropical disturbance also is not associated with a front and maintains its identity for 24 hours or more.


More weather terms to know


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