Eyewall replacement cycle; in most hurricanes the eye simply collapses every 12-24 hours and another eye forms. The storm spreads out a bit, but weakens considerably while this happens. (One of our excellent hurricane experts can explain the technical details, that's just the simple explanation that I can remember.)
The reason you hear people on here worrying about "annular" hurricanes is that annular storms don't undergo eyewall replacements; they've reached a steady state where they can sustain themselves without the eye having to collapse and reform.
}:-)4
So what's a "stadium effect". I'm assuming its NOT in reference to the need to go to the Superdome!?
Basically what happens is that as a hurricane intensifies, the eye shrinks considerably in diameter (as the cyclonic voriticity increases) until the storm's center is wrapped very tightly about a very small radius of about 5-15 miles. As this occurs, rain bands outside of the eyewall can begin to strengthen. The strengthening of the rainbands immediately adjacent to the storm's core robs the inner eyewall of the fuel (moisture and energy) for the inner eyewall to exist, and so it dissipates.
Those outer rainbands subsequently become the main eyewall and it too, in turn, will shrink in diameter as the storm intensifies again. This eyewall regeneration cycle (EWRC) can occur several times in the life of a hurricane.