Observations made in and around tropical cumuli in the vicinity of Puerto Rico have been used to determine the presence of precipitation and to obtain estimates of cloud buoyancy. It is shown that the development of precipitation was related to the buoyancy characteristics of the cloud prior to the formation of rain and to the environmental conditions of humidity and vertical wind shear. In addition, the effects of treating clouds with a water spray have been evaluated through the use of the buoyancy-precipitation relationships observed in untreated clouds.