CAT sometimes occurs in areas where there is darkening in satellite pictures taken in the infra-red 'water vapour' channel. Here, strong downward movement of the air gives rise to warmer and drier air, resulting in darker shades on the satellite picture.
A suspected CAT event occurred near Macau on 17 October 1999, around noon Hong Kong time. Satellite pictures taken at around that time reveal the said darkening over the event area (yellow circle).
There are also other patterns on satellite pictures that are known to be associated with CAT.
Figure 1: 'Water vapour' pictures taken by
the Geostationary Meteorological Satellite
of Japan Meteorological Agency