A storm system was dumping a great amount of rain over Rio de Janeiro when the sky over Saquarema, 80 km to the East, suddenly became filled with mammatus formations. It seemed to be reverberating with the impact of the approaching thunderstorm as it was possibly under the anvil of the same huge cumulonimbus system. Mammatus clouds, that resemble pouches, are formed by descending cold air and usually herald the approach of severe weather conditions. Fortunately, the core of the storm missed us as the wind carried it out to the sea.

Nikon CoolPix P900 camera at manual mode

PhotoScape to slightly enhance contrast and compensate for backlight.