"Central Dense Overcast", or CDO is the cirrus cloud shield of the storm that results from the thunderstorms in the eyewall of a tropical cyclone and its rainbands. The CDO is typically uniform, showing the cold cloud tops of the cirrus with no eye apparent prior to the tropical cyclone reching hurricane strength (33 m/s, 64 kts, 74mph).Tropical cyclones that have nearly circular CDO's are indicative of favorable, low vertical shear environments. Once the storm reaches hurricane strength an eye can usually be seen in either the infrared or visible channels of the satellites.