Tropical cyclones usually exhibit an annular region of low vorticity, or moat, outside their inner eyewalls. In this region, convective clouds are usually suppressed. Although subsidence plays a significant role in this region, there are additional dynamics, which we explore, that play a role in this region.

Rotation-dominated regions of a TC can be distinguished from strain-dominated regions by comparing the relative magnitudes of the total rate of strain and relative vorticity. Within the radius of maximum tangential wind the flow is rotation dominated so that coherent structures such as mesovortices can survive for long periods. Outside the radius of maximum tangential wind the flow is often strain-dominated, resulting in filamented patches of anomalous vorticity. In the regions of strain-dominated flow we can define a filamentation time. In a tropical cyclone, an annular region can exist just outside the radius of maximum tangential wind and approximately 30 km wide, where the filamentation time is less than 30 min and often as small as 5 min. We define this region as the rapid filamentation zone. Since the time scale for deep moist convective overturning is approximately 30 min, deep convection can be significantly distorted and even suppressed in the rapid filamentation zone. A nondivergent model illustrates the effects of rapid filamentation zones in category 1 through 5 TCs and demonstrates the evolution of such zones during binary vortex interaction and during mesovrtex formation from a thin annular ring of enhanced vorticity.