ATLANTIC — The National Hurricane Center assigns numbered designations to tropical depressions and names to tropical storms during the Atlantic hurricane season. This season operates from June 1 through November 30.

A tropical cyclone is a rotating storm system with organized thunderstorms and a defined circulation that forms over warm tropical or subtropical waters. It begins as a tropical disturbance, characterized by an area of disorganized showers and thunderstorms in the tropics. A tropical disturbance may show some signs of circulation but does not have a well-defined center.

Progression leads to a tropical depression, which is a system with a closed circulation and maximum sustained winds of 38 mph or less. The National Hurricane Center numbers these depressions, but they are not given official names. Once sustained winds reach between 39 mph and 73 mph, the system becomes a tropical storm, and the National Hurricane Center assigns it a name from a predetermined list.

A hurricane indicates maximum sustained winds of at least 74 mph. These storms are categorized on the Saffir-Simpson Hurricane Wind Scale, from Category 1 to Category 5, based on their wind speed. Storms forming in the Atlantic and eastern Pacific are called hurricanes, while similar storms in the western Pacific are known as typhoons. Storms in the Indian Ocean and parts of the South Pacific are often referred to as cyclones.

Most tropical systems develop over waters that are at least 80 degrees Fahrenheit. Favorable atmospheric conditions for these systems include moist air and low wind shear.