This site contains information about one of the more difficult problems for operational tropical cyclone forecasters, which is the assessment of the cyclone's maximum sustained surface wind. When aircraft reconnaissance data are available, they are typically obtained from the 700 mb (10,000 ft) level and from these flight-level observations the forecaster is left to estimate the surface winds. In 1997, hurricane reconnaissance aircraft began to deploy global positioning system (GPS) -based dropwindsondes in the hurricane eyewall. These instruments provide, for the first time, detailed, accurate profiles of the inner core of a hurricane from flight level (typically 700 mb) down to the surface. This site explains how these profiles are interpreted and how the conclusion can be applied to high-rise buildings.