The formation of tropical cyclones within a few degrees latitude of the Equator is investigated using European Centre for Medium Range Weather Forecasts (ECMWF) analyses of some prominent cyclogenesis events there. The possibility of formation at the Equator is demonstrated also using idealized model simulations, starting from a prescribed, weak initial counterclockwise vortex in an otherwise quiescent, nonrotating environment. 

In the real events investigated, vortex formation occurred within a broad-scale counterclockwise flow that encompassed a region of predominantly positive absolute vertical vorticity. Patches of enhanced vertical vorticity form within this region as a result of vorticity stretching by deep convection. These vorticity patches are organized by the convection, the collective effects of which are to produce an overturning circulation that fluxes vorticity at low levels towards some centre within the convective region.