Eye and Center
A strong tropical cyclone will harbor an area of sinking air at the center of circulation. If this area is strong enough, it can develop into a large "eye". Weather in the eye is normally calm and free of clouds, although the sea may be extremely violent. The eye is normally circular in shape, and is typically 30–65 km (19–40 mi) in diameter, though eyes as small as 3 km (1.9 mi) and as large as 370 km (230 mi) have been observed. Intense, mature tropical cyclones can sometimes exhibit an outward curving of the eyewall's top, making it resemble an arena football stadium; this phenomenon is sometimes referred to as the stadium effect. It is usually warmest in the center.
There are other features that either surround the eye, or cover it. The central dense overcast is the concentrated area of strong thunderstorm activity near the center of a tropical cyclone; in weaker tropical cyclones, this feature may cover the center completely. The eyewall is a circle of strong thunderstorms that surrounds the eye; this is where the greatest wind speeds are found, clouds reach the highest, and precipitation is the heaviest. The heaviest wind damage occurs where a tropical cyclone's eyewall passes over land. Eyewall replacement cycles occur naturally in intense tropical cyclones. When cyclones reach peak intensity, they usually have an eyewall and radius of maximum winds that contract to a very small size, around 10 to 25 km (6.2 to 16 mi). Outer rainbands can organize into an outer ring of thunderstorms that slowly moves inward and robs the inner eyewall of its needed moisture and angular momentum. When the inner eyewall weakens, the tropical cyclone weakens, as its maximum sustained winds weaken and the central pressure rises). The outer eyewall replaces the inner one completely at the end of the cycle. The storm can retain much of its intensity during the cycle, and may even strengthen again afterwards as it builds a new outer ring for the next eyewall replacement.
Read more about this topic: Tropical Meteorology, Physical Structure
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