<P> An extratropical cyclone is a synoptic scale low pressure weather system that has neither tropical nor polar characteristics, being connected with fronts and horizontal gradients in temperature and dew point otherwise known as "baroclinic zones". </P> <P> The descriptor "extratropical" refers to the fact that this type of cyclone generally occurs outside of the tropics, in the middle latitudes of the planet, where the Westerlies steer the system generally from west to east . These systems may also be described as "mid-latitude cyclones" due to their area of formation, or "post-tropical cyclones" where extratropical transition has occurred, and are often described as "depressions" or "lows" by weather forecasters and the general public . These are the everyday phenomena which along with anti-cyclones, drive the weather over much of the Earth . </P> <P> Although extratropical cyclones are almost always classified as baroclinic since they form along zones of temperature and dewpoint gradient, they can sometimes become barotropic late in their life cycle when the temperature distribution around the cyclone becomes fairly uniform along the radius from the center of low pressure . An extratropical cyclone can transform into a subtropical storm, and from there into a tropical cyclone, if it dwells over warm waters and develops central convection, which warms its core and causes temperature and dewpoint gradients near their centers to fade . </P> <P> When a tropical cyclone crosses the subtropical ridge axis, normally through a break in the high - pressure area caused by a system traversing the Westerlies, its general track around the high - pressure area is deflected significantly by winds moving towards the general low - pressure area to its north . When the cyclone track becomes strongly poleward with an easterly component, the cyclone has begun recurvature, entering the Westerlies . A typhoon moving through the Pacific Ocean towards Asia, for example, will recurve offshore of Japan to the north, and then to the northeast, if the typhoon encounters southwesterly winds (blowing northeastward) around a low - pressure system passing over China or Siberia . Many tropical cyclones are eventually forced toward the northeast by extratropical cyclones in this manner, which move from west to east to the north of the subtropical ridge . An example of a tropical cyclone in recurvature was Typhoon Ioke in 2006, which took a similar trajectory . </P>

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