A lot of people get confused by various meteorological terms related to storms. The main thing to remember here is that the labels have to do with the relative strength, sustained winds, and organized formation of the weather disturbance.
A tropical depression happens when a low pressure area forms and comes with thunderstorms. The circular wind flow that these thunderstorms create must pack maximum sustained winds of no more than 38mph. If the sustained winds get to between 39 and 73 mph—and if it shows a more organized or closed center cyclonic distribution—it is elevated to a tropical storm.
Image source: nationalgeographic.com
The word “tropical” is added as these low pressure systems develop over the tropics. Tropical depressions and storms are generally called “cyclones” because they spin in a counter-clockwise manner. Before becoming a depression or a storm, these cyclones are simply called a tropical disturbance since they don’t have a closed center of circulation.
If a tropical storm reaches strengths of 74 mph winds or above, it would then be upgraded to a full-fledged hurricane or typhoon, depending on where exactly in the world the storm occurs.
Image source: thezebra.com
Jim Byrne is a weatherman currently serving as consulting meteorologist for the Weather Channel program “So You Think You’d Survive.” He was previously the chief meteorologist for KCOY CBS-12. For more insights on everything related to the weather, visit this blog.