Central dense overcast

Southern hemisphere tropical cyclone Winston with a large CDO surrounding its eye

It is a large region of thunderstorms surrounding the center of stronger tropical and subtropical cyclones which shows up brightly (with cold cloud tops) on satellite imagery.[1][2][3] The CDO forms due to the development of an eyewall within a tropical cyclone.[4] Its shape can be round, oval, angular, or irregular.[5] Its development can be preceded by a narrow, dense, C-shaped convective band. Early in its development, the CDO is often angular or oval in shape, which rounds out, increases in size, and appears more smooth as a tropical cyclone intensifies.[6] Rounder CDO shapes occur in environments with low levels of vertical wind shear.[2]

The strongest winds within tropical cyclones tend to be located under the deepest convection within the CDO, which is seen on satellite imagery as the coldest cloud tops.[7] The radius of maximum wind is usually collocated with the coldest cloud tops within the CDO,[7] which is also the area where a tropical cyclone's rainfall reaches its maximum intensity.[8] For mature tropical cyclones that are steady state, the CDO contains nearly no lightning activity, though lightning is more common within weaker tropical cyclones and for systems fluctuating in intensity.[9]

The eye is a region of mostly calm weather at the center of the CDO of strong tropical cyclones. The eye of a storm is a roughly circular area, typically 30–65 kilometres (19–40 mi) in diameter. It is surrounded by the eyewall, a ring of towering thunderstorms surrounding its center of circulation. The cyclone's lowest barometric pressure occurs in the eye, and can be as much as 15% lower than the atmospheric pressure outside the storm.[10] In weaker tropical cyclones, the eye is less well-defined or nonexistent, and can be covered by high cloudiness caused by cirrus cloud outflow from the surrounding central dense overcast.[10]

Common developmental patterns seen during tropical cyclone development, and their Dvorak-assigned intensities

Within the Dvorak satellite strength estimate for tropical cyclones, there are several visual patterns that a cyclone may take on which define the upper and lower bounds on its intensity. The central dense overcast (CDO) pattern is one of those patterns. The central dense overcast utilizes the size of the CDO. The CDO pattern intensities start at T2.5, equivalent to minimal tropical storm intensity, 40 mph (64 km/h). The shape of the central dense overcast is also considered. The farther the center is tucked into the CDO, the stronger it is deemed.[5] Banding features can be utilized to objectively determine the tropical cyclone's center, using a ten degree logarithmic spiral.[11] Using the 85–92 GHz channels of polar-orbiting microwave satellite imagery can definitively locate the center within the CDO.[12]

Tropical cyclones with maximum sustained winds between 65 mph (105 km/h) and 100 mph (160 km/h) can have their center of circulations obscured by cloudiness within visible and infrared satellite imagery, which makes diagnosis of their intensity a challenge.[13] Winds within tropical cyclones can also be estimated by tracking features within the CDO using rapid scan geostationary satellite imagery, whose pictures are taken minutes apart rather than every half-hour.[14]