What's a stadium effect?
When the sat photo of the eye looks like you are peering down into a bowl-shaped stadium
Stadium Effect
The stadium effect is a rare phenomenon appearing in hurricanes in which the inward curvature of the cumulonimbi top forming the eyewall of the hurricane creates an open dome that resembles a football stadium. Its presence implies a mature and very intense hurricane/typhoon. The strongest typhoon/hurricane ever seen on record was Typhoon Tip (1979) with an estimated minimum sea level pressure of 870 mbar.
http://en.wikipedia.org/wiki/Stadium_effect
