Cyclones come in four types: tropical disturbances, tropical depressions, tropical storms and hurricanes. Cyclones are classified according to their size and strength; wind speed is the primary differentiating factor. These storms form in the tropics, and they may arise in the Northern and Southern hemisphere alike.
Of the cyclone family, tropical disturbances are the smallest. They have winds under 30 miles per hour (MPH), and produce light rain. Tropical depressions have winds less than 39 MPH and more organized centers. Tropical storms sustain wind speeds between 39 and 74 MPH, while hurricanes are the largest of all cyclones, and they produce winds in excess of 74 MPH.