The eyewall is the region of a tropical cyclone where the winds are the highest, the clouds reach furthest into the atmosphere and the precipitation is the heaviest. It is the area directly around the eye of the cyclone. The heaviest damage caused by tropical cyclones occurs where the eyewall crosses over land. The strongest tropical cyclones have the eyewall wrapped completely around the eye of the storm; storms where the eyewall does not completely wrap around the eye are not as strong or as well-formed.
In many major tropical cyclones, the storm will undergo an eyewall replacement cycle. In this process, the eyewall contracts to a smaller size, and outer rain bands form a new eyewall. This new eyewall weakens the original, and eventually replaces it completely. During the replacement cycle, the storm weakens, sometimes dramatically, but afterwards the storm will often be stronger than before. On rare occasion, additional concentric eyewalls will form.