In the tropics or subtropics, an organized, but non-frontal, system of convective clouds around a low-pressure centre, with closed isobars and circulation. These systems tend to occur where there is convergence, especially along the Intertropical Convergence Zone. The maximum sustained (1-minute mean) wind speeds are less than 18 m s−1 (approximately force 7 on the Beaufort scale). Although most do not develop further, some may intensify sufficiently to be called a tropical storm, and even subsequently evolve into a tropical cyclone.
Subjects: Meteorology and Climatology.