Kelvin-Helmholtz billows in the eyewall of Hurricane Erin

A photograph of vertically aligned Kelvin-Helmholtz billows in the eastern eyewall of Hurricane Erin on 10 September 2001 is presented. The vertical shear instability in the horizontal winds necessary to produce the billows is confirmed with a high-altitude dropwindsonde observation. This shear instability is not known to be common in tropical cyclone eyewalls and is likely only in cases with a very large eyewall tilt. However, research and reconnaissance aircraft pilots need to be aware of: the possibility of their existence, along with other types of hazardous conditions, in such rare circumstances.