<P> The formation of tropical cyclones is the topic of extensive ongoing research and is still not fully understood . While six factors appear to be generally necessary, tropical cyclones may occasionally form without meeting all of the following conditions . In most situations, water temperatures of at least 26.5 ° C (79.7 ° F) are needed down to a depth of at least 50 m (160 ft); waters of this temperature cause the overlying atmosphere to be unstable enough to sustain convection and thunderstorms . For tropical transitioning cyclones (i.e. Hurricane Ophelia (2017)) a water temperature of at least 22.5 ° C (72.5 ° F) has been suggested . </P> <P> Another factor is rapid cooling with height, which allows the release of the heat of condensation that powers a tropical cyclone . High humidity is needed, especially in the lower - to - mid troposphere; when there is a great deal of moisture in the atmosphere, conditions are more favorable for disturbances to develop . Low amounts of wind shear are needed, as high shear is disruptive to the storm's circulation . Tropical cyclones generally need to form more than 555 km (345 mi) or five degrees of latitude away from the equator, allowing the Coriolis effect to deflect winds blowing towards the low pressure center and creating a circulation . Lastly, a formative tropical cyclone needs a preexisting system of disturbed weather . Tropical cyclones will not form spontaneously . Low - latitude and low - level westerly wind bursts associated with the Madden - Julian oscillation can create favorable conditions for tropical cyclogenesis by initiating tropical disturbances . </P> <P> Most tropical cyclones form in a worldwide band of thunderstorm activity near the equator, referred to as the Intertropical Front (ITF), the Intertropical Convergence Zone (ITCZ), or the monsoon trough . Another important source of atmospheric instability is found in tropical waves, which contribute to the development of about 85% of intense tropical cyclones in the Atlantic Ocean and become most of the tropical cyclones in the Eastern Pacific . The majority forms between 10 and 30 degrees of latitude away of the equator, and 87% forms no farther away than 20 degrees north or south . Because the Coriolis effect initiates and maintains their rotation, tropical cyclones rarely form or move within 5 degrees of the equator, where the effect is weakest . However, it is still possible for tropical systems to form within this boundary as Tropical Storm Vamei and Cyclone Agni did in 2001 and 2004, respectively . </P> <P> The movement of a tropical cyclone (i.e. its "track") is typically approximated as the sum of two terms: "steering" by the background environmental wind and "beta drift". </P>

Where do the disturbances that cause tropical storms originate
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