Development and Rapid Intensification of Tropical Cyclone OCKHI (2017) over the North Indian Ocean

Abstract

Tropical Cyclone OCKHI over the North Indian Ocean during 2017 underwent dramatic development and rapid intensification very close to the land - Sri Lanka, extreme South Indian coast and Lakshadweep area during its initial developmental stage and caused extensive damages over these areas. On examining the physical and structural mechanism involved in such development, it is observed that the initial development was associated with axi-symmetrisation of the vortex that could be associated with Vortex Rossby waves near the eyewall. Associated with the expulsion of high vorticity from the centre during asymmetry mixing, there was outward propagation of eddy angular momentum flux in the lower levels that strengthened a low level anticyclone to the northeast of the TC centre which in turn enhanced the cyclonic inflow near the TC centre. The rapid intensification phase was associated with vertical non-uniform heating with upper and lower tropospheric warming associated with latent heat release in convection. During the mature phase, the system sustained ‘very severe’ intensity even under increasing vertical shear and lower ocean heat flux under the influence of a break in the sub tropical ridge to the north of the system centre that enhanced the poleward outflow in the upper troposphere.