Early this July Tropical Storm Chantal began churning through the Caribbean; it gained power and then weakened until it ultimately dissipated on July 10. While it was still a threat as a storm, it wasn’t yet a hurricane. So what’s the difference between a storm and a hurricane? And what’s a tropical depression? As with many natural systems, hurricanes evolve through a life cycle of developmental stages from birth to death, a process that can take several weeks. An oceanic tropical disturbance over time can progress from a tropical depression (first stage) to a tropical storm (second stage) to its most intense stage as a hurricane (third stage) by attaining a specified sustained wind speed.
Hurricanes can often live and cause damage for a long period of time—as much as two to three weeks. In their very earliest stages they may begin as a group of thunderstorms over the tropical ocean waters; these storms can then coalesce into a single, larger tropical disturbance—a depression. After a disturbance has evolved into a tropical depression and begins gaining more power and wind speed, the amount of time it takes to achieve the next stage, a tropical storm, can take from half a day to several days. A tropical depression typically has wind speeds of approximately 38 miles per hour. But depressions can weaken and never become a storm. The same time frame may occur for a tropical storm to intensify into a hurricane—and the storm can weaken and it may never achieve hurricane force winds and official hurricane status.
As the depression’s wind speed increases and reaches 39-73 miles per hour it becomes a tropical storm, and with further wind speed gains it can become a Category 1 hurricane with winds of 74-95 miles per hour. A Category 5 hurricane can have sustained winds greater than 150 miles per hour.
Atmospheric and oceanic conditions play major roles in determining these events, with water and air temperatures being key factors affecting whether a storm progresses to a hurricane. So the simplest answer to what is the difference between a depression and a hurricane is wind speed; the difference between 38 miles and 74 miles per hour.
Crawford helps manage the effects of hurricanes—such as Superstorm Sandy in 2012— through its Catastrophe Services (CAT), the insurance industry’s leading independent adjusting resource for claims management in response to natural and man-made disasters, and also through its Global Technical Services business (GTS®), which focuses on large, complex losses. Learn more here.