Infrared satellite photographs of the tropical oceanic regions within and around the GATE A/B array point to the existence of large, rapidly growing, cumulonimbus clouds. The region along 10°N experiences the greatest frequency of these storms. Also a pronounced diurnal variation is found in the times of initial development with maximum frequencies near midnight. In most cases, this anvil cloud grows to an areal extent ∼7000 km2 in about 4 h, then dissipates in another 3 h. The velocity divergence in the anvil is 1−3×10−4s−1 and the mass outflow is 100–200 kton s−1. These storms account for some of the difference in diurnal variation of high cloudiness that is observed between tropical oceanic and continental regions. A large number of rapidly growing cumulonimbus clouds was observed on 10 August 1974 in connection with a disturbance in the tropical easterlies that ultimately developed into Tropical Storm Alma.