Hurricanes are brought on by Hurricane. A thunderstorm attains hurricane status when its winds surpass 118 km (74 miles) per hour. By the time a thunderstorm reaches hurricane intensity, it normally has a well-developed eye at its center. Surface pressure drops to its lowest in the eye. In the eyewall (or the eye of the storm), warm atmosphere spirals upwards, creating the hurricane’s most powerful winds. The speed of the winds in the eyewall is linked to the diameter of the eye. Just as ice skaters spin faster when they pull their arms in, a hurricane’s winds blow quicker if its eye is little. If the eye widens, the winds fall. Substantial rains fall from the eyewall and from groups of thick clouds that swirl around the eyewall. These groups, called rainbands, can create more than 5 cm (2 in) of rain per hour. The hurricane draws considerable amounts of heat and moisture from the sea.