The
maximum sustained wind associated with a
tropical cyclone is a common indicator of the intensity of the storm. Within a mature tropical cyclone, it is found within the
eyewall at a distance defined as the
radius of maximum wind, or RMW. Unlike
gusts, the value of these
winds are determined via their sampling and averaging the sampled results over a period of time. Wind measuring has been standardized globally to reflect the winds at above the
Earth's surface, and the maximum sustained wind represents the highest average wind over either a one-minute (US) or ten-minute time span (see the definition, below), anywhere within the tropical cyclone. Surface winds are highly variable due to friction between the atmosphere and the Earth's surface, as well as near hills and mountains over land.