Hurricane Structure

Tropical cyclones typically have a well-defined “eye” at the center of circulation where no storms are occurring and wind speeds are relatively light. The eye of a tropical cyclone is typically 10-40 miles in diameter. Surrounding the eye is the strongest convection within a hurricane, known as the eyewall. Bands of strong storms and heavy rainshowers are usually observed spiraling outward from the center of circulation.

There’s typically rising motion within the rainbands and the eyewall, leading to the strong thunderstorms and heavy showers. However, within the eye is typically sinking air, which leads to the mostly clear or partly cloudy skies over the eye itself. Once the rising air within the eyewall and the rainbands reaches the top of the convection, it typically spreads out away from the eye toward the outer edges of the tropical cyclone. While surface winds within the tropical cyclone are spiraling counter-clockwise toward the center of low pressure, upper-level winds are spiraling outward clockwise away from the center of low pressure. This creates an upper-level anticyclone, which can often be observed within mature hurricanes.

Hurricane intensity can be measured either by the lowest surface pressure at the center of the storm or the strongest winds created by the storm. The lowest surface pressure is typically found at the center of the eye of a mature tropical cyclone. The strongest winds within the tropical cyclone are typically within the eyewall, just above the surface. The lowest recorded minimum pressure within a tropical cyclone within the Atlantic basin was 882 millibars within Hurricane Wilma in 2005. The strongest peak sustained wind speeds ever observed from a tropical cyclone in the Atlantic basin were from Hurricane Alan in 1980, which produced 190mph winds.