The eye is a region of mostly calm weather at the center of a tropical cyclone. It is roughly circular, and is typically 30 to 65 kilometers (19 to 40 miles) in diameter. The eye is surrounded by the eyewall, a ring of towering thunderstorms where the most severe weather and highest winds of the storm occur. In strong tropical cyclones, the eye is characterized by light winds and clear skies, surrounded on all sides by a towering, symmetric eyewall, while in weaker storms, it is less well defined and may be covered by a central dense overcast. Weaker or disorganized storms may also feature an eyewall that does not completely encircle the eye or have an eye that features heavy rain. In all storms, however, the eye is the location of the storm's minimum barometric pressure; this can be as much as 15 percent lower than the pressure outside the storm. This photograph, taken by the German astronaut Alexander Gerst from the International Space Station in September 2018, shows the well-defined eye of Hurricane Florence in the Atlantic Ocean.Photograph credit: Alexander Gerst