<P> Since they form from extratropical cyclones, which have colder temperatures aloft than normally found in the tropics, the sea surface temperatures required is around 23 degrees Celsius (73 ° F) for their formation, which is three degrees Celsius (5 ° F) lower than for tropical cyclones . This means that subtropical cyclones are more likely to form outside the traditional bounds of the hurricane season . Although subtropical storms rarely have hurricane - force winds, they may become tropical in nature as their cores warm . </P> <P> A tropical cyclone is a storm system characterized by a low - pressure center and numerous thunderstorms that produce strong winds and flooding rain . A tropical cyclone feeds on heat released when moist air rises, resulting in condensation of water vapour contained in the moist air . They are fueled by a different heat mechanism than other cyclonic windstorms such as nor'easters, European windstorms, and polar lows, leading to their classification as "warm core" storm systems . </P> <P> The term "tropical" refers to both the geographic origin of these systems, which form almost exclusively in tropical regions of the globe, and their dependence on Maritime Tropical air masses for their formation . The term "cyclone" refers to the storms' cyclonic nature, with counterclockwise rotation in the Northern Hemisphere and clockwise rotation in the Southern Hemisphere . Depending on their location and strength, tropical cyclones are referred to by other names, such as hurricane, typhoon, tropical storm, cyclonic storm, tropical depression, or simply as a cyclone . </P> <P> While tropical cyclones can produce extremely powerful winds and torrential rain, they are also able to produce high waves and a damaging storm surge . Their winds increase the wave size, and in so doing they draw more heat and moisture into their system, thereby increasing their strength . They develop over large bodies of warm water, and hence lose their strength if they move over land . This is the reason coastal regions can receive significant damage from a tropical cyclone, while inland regions are relatively safe from strong winds . Heavy rains, however, can produce significant flooding inland . Storm surges are rises in sea level caused by the reduced pressure of the core that in effect "sucks" the water upward and from winds that in effect "pile" the water up . Storm surges can produce extensive coastal flooding up to 40 kilometres (25 mi) from the coastline . Although their effects on human populations can be devastating, tropical cyclones can also relieve drought conditions . They also carry heat and energy away from the tropics and transport it toward temperate latitudes, which makes them an important part of the global atmospheric circulation mechanism . As a result, tropical cyclones help to maintain equilibrium in the Earth's troposphere . </P>

Cyclonic storms can form within or between air masses