eyewalls

An eyewall is a ring of intense convective activity that encircles the eye of a mature tropical cyclone, and in some larger extratropical cyclones it can also appear. It is the most powerful segment of the storm, where the strongest winds, the most intense rainfall, and the strongest storm surge are typically concentrated. The eyewall forms because of the radial outflow at the top of the storm and the convergence of moist air at lower levels; this convergence forces air upward, generating deep convection that organizes into a circular band.

The eyewall is usually located 30 to 70 kilometers from the storm center and has a diameter of about 30 to 70 kilometers. Wind speeds within the eyewall can reach or exceed 150 km/h (90 mph), surpassing those near the outer rainbands. The pressure gradient force is strongest where the pressure falls most steeply, which occurs in this region. Satellite and radar observations show that the eyewall often contains a series of tightly spaced rain bands that merge into a tight, elongated wall of cloud.

In many intense tropical cyclones, the eyewall undergoes a replacement cycle. An outer eyewall forms and gradually expands while the inner eyewall weakens, eventually causing the storm to temporarily weaken, only to later redevelop a stronger inner eyewall. This process can lead to fluctuations in maximum wind speed and central pressure, influencing forecasting of storm intensity.

Because the eyewall contains the most destructive forces of a cyclone, its dynamics are a major focus of hurricane research. Understanding eyewall formation, maintenance, and replacement is essential for improving intensity prediction and for assessing the risk posed to coastal communities.