A typhoon is a tropical cyclone that develops between 180° and 100°E in the Northern Hemisphere, specifically in the Northwestern Pacific Basin, accounting for almost one-third of the worlds annual tropical cyclones. Typhoons are the same weather phenomenon as hurricanes, and both are classified as tropical cyclones. The term "typhoon" is used to refer to a tropical cyclone that develops in the Northwest Pacific Ocean, usually East Asia, while the term "hurricane" is used in the North Atlantic, central North Pacific, and eastern North Pacific. Tropical cyclones are rotating, organized systems of clouds and thunderstorms that develop over warm tropical or subtropical waters and are characterized by low atmospheric pressure, high winds, and heavy rain. The main parts of a tropical cyclone are the rainbands, the eye, and the eyewall. Air spirals in toward the center in a counter-clockwise pattern in the northern hemisphere (clockwise in the southern hemisphere), and out the. Tropical cyclones officially become tropical storms when winds reach 39 miles per hour, and they become hurricanes or typhoons at 74 mph, at which point they are classified by levels and additional titles. Since 2009, the Hong Kong Observatory has divided typhoons into three different classifications: typhoon, severe typhoon, and super typhoon. A typhoon has wind speed of 64–79 knots (73–91 mph; 118–149 km/h), a severe typhoon has winds of at least 80 knots (92 mph; 150 km/h), and a super typhoon has winds of at least 100 knots (120 mph; 190 km/h) .