The present work is concerned with the study of intensification of tropical disturbances with a view to improve prediction and early warning. The tropical disturbances are known to come in sizes (radii) ranging from 100–400 kms. Since the vortices of different sizes give rise to different initial convergence fields and since the subsequent development of the tropical depressions is very sensitive to the initial convergence fields, we argue that the size of the incipient vortex is likely to be an important factor in determining the subsequent development of a tropical disturbance.
We have examined the above hypothesis using an axisymmetric model of tropical cyclone. The incipient vortex is introduced by prescribing an initial temperature perturbation with wind in gradient balance. The results show a fairly sharp selection of scale at about 250 km radius. This implies that out of a number of initial disturbances of varying sizes and embedded in the same large scale environment, it is the vortex with about 250 km radius size that will develop to the most severe system. The sensitivity of this selective intensification at this incipient vortex radius to initial perturbation field and the mean thermodynamic state is investigated. Finally, the importance of such a selective scale of intensification for prediction, tracking and early warning of tropical cyclones is emphasized.