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    If the six conditions, we’ve covered in previous chapter, are met, the tropical cyclone appears. Let's now learn what phases there are to grow from the tropical disturbance of the atmosphere to a huge tropical cyclone.

    It starts with a tropical disturbance

    At the beginning of every tropical cyclone, there is a tropical disturbance or a wave that can be caused for example by thunderstorm going from a land above an ocean. In this phase, previously mentioned six conditions play a big role to start the engine of development.

    What is a tropical depression

    In the next phase, the wind rises and starts to circle a centre of the disturbance due to the Coriolis force. Now it’s called tropical depression and it is a measurable and observable object in the atmosphere with clouds slightly rotating around causing low precipitation.

    Almost a Hurricane

    When the wind speed reaches 39 mph (63 km/h), it is called a tropical storm. Tropical storm looks like a little hurricane, but it has no eye in its centre. It is all covered in clouds spinning around an invisible centre.

    In this phase, the storm gets a name. It can stop growing here and the name will be already used for only tropical storm and not for a cyclone (like was a case with recent tropical storm Ivo that weakened to tropical depression). More on tropical storm naming in following chapters. Anyway, even tropical storms can make huge damage.

    When Tropical storm becomes a Hurricane

    Finally, tropical cyclone is a phase with wind speed above 74 mph (119 km/h). It has a fully developed eye in the centre and its structure is quite stable above an ocean.

    There are different names for tropical cyclones based on location, they are called hurricanes in the Atlantic Ocean and north-eastern Pacific Ocean, typhoons in the north-western Pacific Ocean and simply cyclones in South Pacific and Indian Ocean.

    Before we get to more details in the upcoming chapters, we’ll uncover the difference between tropical and extratropical cyclone in the next one. See you next chapter.

    Štěpán Šubík

    Prague based student of meteorology eager for science, who likes to learn, but also wants to live to the fullest every day. Follow me on Twitter.

    Next chapters:

    • What is the difference between tropical and extratropical cyclone
    • What’s the difference between hurricane, typhoon, cyclone

    Previous chapters:


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