Characteristics of a southerly thunderstorm at DumDum (22.38°N, 88.28°) and nearby coastal areas

Abstract

On 29 April 1989, a widespread southerly thunderstorm occurred over DumDum along with some other nearby coastal areas. These developments neither occurred in any synoptically favourable areas nor around the position of dry line. The associated changes of pressure and temperature at the surface at the time of occurrence over DumDum were unusual. The low depth of convective instability and high value of vertical shear of horizontal wind speed around the lifting condensation level support the low depth of cumulonimbus cloud over DumDum whereas the moderate value of bulk Richardson number signified that it would have a supercell structure. The surface parameter S developed from surface pressure, temperature and dew point of 0830 IST data only is found suitable for giving an idea of their occurrence.