an organized region of showers and thunderstorms in the tropics - generally 200 to 600 kilometres in diameter - that maintains its identity for at least 24 hours but does not have a closed wind circulation
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Valdkond ICAO lisade põhjal loodud klassifikaatori järgi: Lennumeteoroloogia
Troopilise tsükloni arengut jälgitakse neljas etapis. Kuna ekvaatori lähedal on tuul tavaolukorras väga nõrk, siis 10 m/s puhuva tuule korral nimetatakse tekkinud õhulainet troopiliseks häirituseks. Kui isobaarid (õhurõhu samajooned) on juba sulgunud ning tuul ulatub kuni 17 m/s, siis nimetatakse pöörist troopiliseks depressiooniks. 17-33 m/s tuule kiiruse korral kutsutakse pöörist troopiliseks tormiks ja talle antakse nimi (tuule kiirus kuni 33 m/s).
A circulation system goes through a sequence of stages as it intensifies into a mature tropical cyclone. The storm begins as a tropical disturbance, which typically occurs when loosely organized cumulonimbus clouds in an easterly wave begin to show signs of a weak circulation. Once the wind speed increases to 36 km (23 miles) per hour, the storm is classified as a tropical depression. If the circulation continues to intensify and the wind speeds exceed 63 km (39 miles) per hour, then the system is called a tropical storm. Once the maximum wind speed exceeds 119 km (74 miles) per hour, the storm is classified as a tropical cyclone.
