Tropical weather disturbances typically begin as areas of rough weather and thunderstorms in the tropics, geographically defi ned as the area 23.5°north and 23.5°south of the equator. Throughout the year, this area receives high quantities of solar insolation (exposure to sunlight). The heated tropical seas release moist warm air that produces bands of rain and low pressure areas around the equator. A convergence of moisture, heat, and wind systems in the tropics can lead to thunderstorms──weather disturbances that produce heavy rains and gusting winds.

A group of thunderstorms can organize as the winds increase around the moist, low pressure air. When the winds reach a constant between 20 and 34 knots, the disturbance is classifi ed as a tropical depression. Each year, hundreds of tropical depressions occur worldwide, and each one is numbered.

As a tropical system strengthens, its winds spiral inward, concentrating moisture near the center. When the winds swirl counter-clockwise in the northern hemisphere or clockwise in the southern hemisphere around a low pressure system, this is called cyclonic flow. As these winds move away from the equator, they can take advantage of curving winds deflected by the Earth?s rotation (a phenomenon called the Coriolis Effect). The tropical system gains intensity from the winds, and it can become a tropical storm, cyclone, typhoon, or hurricane. When a tropical storm organizes to the point where its sustained winds are more than 34 knots (39 miles per hour), it is designated, by international agreement, a tropical storm. Once the intensity of a tropical weather disturbance exceeds 63 knots, it becomes a tropical cyclone. These storms are characterized by a dark spot found in the middle of the storm the eye. Around the eye are intense winds and bands of rainfall that make up the eye wall. Extending hundreds of kilometers outward from the eye are spiral rain bands ── long, narrow bands of clouds, heavy rain, and high winds.

Tropical cyclone is a generic term; it is called a typhoon in the western north Pacific basin and Asia (Japan) and a hurricane in north and central America. These storms are categorized by maximum sustained wind speed. Three basic classifications exist for levels of typhoon intensity, separately developed and used by the World Meteorological Organization (WMO), the Japan Meteorological Agency (JMA), and the Joint Typhoon Warning Center (JTWC) in the United States.

熱帶天氣擾動特指熱帶地區的暴風雨和雷雨，地理位置介於南北緯23.5度之間的區域屬於熱帶地區，此區終年承受劇烈日照(陽光曝晒)。熱帶海洋受熱之後蒸發暖水氣，在赤道附近形成雨帶與低氣壓。熱帶地區的水氣、熱氣與風系輻合之後，就有機會生成雷雨──挾帶狂風暴雨的天氣擾動。

當潮濕的低氣壓周圍風力增強時，很容易生成連串雷雨。假如風力持續增強，最後維持在20到34節之間，這種擾動就被歸為熱帶低壓。每年有數百個熱帶低壓於世界各地生成，每一個都會加以編號。

一熱帶系統逐漸增強的同時，風會螺旋向內吹拂，將水氣往中心聚集。當這種風出現在低壓系統附近，在北半球呈逆時針旋轉，在南半球呈順時針旋轉，就稱為氣旋式氣流。這些風一邊往赤道外移動，一邊吸收地球自轉所造成的偏轉風(一種稱為科氏效應的現象)。待其吸收到足夠的風力，便可能形成熱帶風暴、氣旋、颱風或颶風。一個熱帶系統發展到持續風速超過34節(每小時39英里)的程度，以國際標準來看就構成了熱帶風暴，一旦超過63 節則演變為熱帶氣旋。它們共同的特徵在於中心有暗點：風暴眼。風暴眼周圍的狂風和雨帶形成眼牆。從風暴眼向外延伸數百公里的部分稱為螺旋雨帶，是充滿強風豪雨的狹長雲帶。

熱帶氣旋只是一個統稱。發生在西北太平洋海盆以及亞洲(日本)的熱帶氣旋稱為颱風，發生在中北美洲的熱帶氣旋稱為颶風。這些風暴以最大持續風速來分級。颱風強度有三種基本分級法，分別由世界氣象組織(WMO)、日本氣象廳(JMA)，以及位於美國的聯合颱風警報中心(JTWC)所規範使用。