Is rapid intensification internally or externally controlled?

In a previous study, the large-scale atmospheric and oceanic environment was examined for tropical cyclones (TCs) undergoing varying levels of intensity change, from weakening to rapidly intensifying. As expected, the environment was found to be significantly less favorable for weakening TCs than intensifying TCs. However, an interesting result from that study was that the composite environment of intensifying/neutral TCs and rapidly intensifying TCs was generally similar; however some variability was found between certain parameters and in different ocean basins.

Using the composite environmental fields from the previous study, an idealized modeling study is conducted using the full-physics tropical cyclone version of the Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS-TC) to test a hypothesis that rapid intensification is largely an internally controlled, and thus less predictable, process. A sequence of numerical simulations is performed in which a tropical storm-like vortex is initialized in different environments filling a designed parameter space with realistically varying levels of humidity, environmental shear, instability, sea surface temperature, and upper and low level divergence and vorticity. The subsequent intensification rate is examined, leading to better guidance on the relative importance of internal versus external control on the TC intensity change.