Conductive heat gains are converted to convective and radiative heat gains. As velocity increases, both convective and radiative heating increase. The total heat flux is composed of a conductive, convective and radiative part. As in summer, precipitation falls mainly during convective thunderstorms. Tropical cyclones form as a result of significant convective activity, and are warm core. There is less rainfall from summer convective showers and thunderstorms than in inland areas. During the remaining months there is a little precipitation due to Convective rains. The vacuum significantly reduces convective heat loss. Thus greenhouses work primarily by preventing convective cooling. A bow echo is associated with squall lines or lines of convective thunderstorms. Larger cumuliform types are a sign of greater atmospheric instability and convective activity. In this season, most rain falls during convective thunderstorms. These storms formed the second of three convective bands to generate tornadoes. The Nusselt number is the ratio of convective to conductive heat transfer across a boundary. Heat is carried away from the heatsink by convective or fan-forced airflow.