Hurricane Isabel (2003) as seen from orbit during Expedition 7 of the International Space Station. The eye, eyewall, and surrounding rainbands, characteristics of tropical cyclones, are clearly visible in this view from space.
A tropical cyclone is a rapidly rotating storm system characterized by a low-pressure center, strong winds, and a spiral arrangement of thunderstorms that produce heavy rain. Depending on its location and strength, a tropical cyclone is referred to by names such as hurricane (/ˈhʌrɨkən/ or /ˈhʌrɨkeɪn/), typhoon /taɪˈfuːn/, tropical storm, cyclonic storm, tropical depression, and simply cyclone.
Tropical cyclones typically form over large bodies of relatively warm water. They derive their energy through the evaporation of water from the ocean surface, which ultimately recondenses into clouds and rain when moist air rises and cools to saturation. This energy source differs from that of mid-latitude cyclonic storms, such as nor'easters and European windstorms, which are fueled primarily by horizontal temperature contrasts. The strong rotating winds of a tropical cyclone are a result of the conservation of angular momentum imparted by the Earth's rotation as air flows inwards toward the axis of rotation. As a result, they rarely form within 5° of the equator. Tropical cyclones are typically between 100 and 2,000 km (62 and 1,243 mi) in diameter.
Hurricane Florence near peak intensity on September 11.
Tropical refers to the geographical origin of these systems, which form almost exclusively over tropical seas. Cyclone refers to their cyclonic nature, with wind blowing counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere. The opposite direction of circulation is due to the Coriolis effect.
In addition to strong winds and rain, tropical cyclones are capable of generating high waves, damaging storm surge, and tornadoes. They typically weaken rapidly over land where they are cut off from their primary energy source. For this reason, coastal regions are particularly vulnerable to damage from a tropical cyclone as compared to inland regions. Heavy rains, however, can cause significant flooding inland, and storm surges can produce extensive coastal flooding up to 40 kilometres (25 mi) from the coastline. Though their effects on human populations are often devastating, tropical cyclones can relieve drought conditions. They also carry heat energy away from the tropics and transport it toward temperate latitudes, which may play an important role in modulating regional and global climate.
Formation[]
A tropical cyclone forms in tropical water, usually in late summer and early fall/autumn. For a tropical cyclone to form, there has to be a warm body of water and light winds.
Stage 1: General rainfall[]
A tropical cyclone almost always starts as a thunderstorm cell
Natural activity of warm water includes evaporation and the formation of clouds. The clouds may result in precipitation and thunderstorms. Because the pressure in the tropical regions is already low, the system can develop more easily. The resulting rainfall warms the air at low altitude, causing it to rise, lowering pressure at low altitude and form a high pressure system at higher altitudes.
Stage 2: Tropical depression[]
The low surface pressure pulls the cluster of rainfall together and rotates it, while also drawing in warm, moist air which feeds the system. The upper-level high pressure pushes the clouds outward and rotates them. The system is now getting stronger as it pulls in more air. The system may develop an "eye"
Stage 3: Tropical storm[]
When winds exceed 38 mph (61 km/h), the system achieves tropical storm status. The system produces torrential rain that worsens closer to the eye and continues to draw in tropical air as surface winds, which continue to get stronger. The system is also named.
Stage 4: Hurricane, typhoon, or tropical cyclone[]
When winds exceed 74 mph (120 km/h), the system is officially a hurricane, typhoon, or tropical cyclone. The system continues to get stronger until it makes landfall or moves into cooler waters.
Dissipation[]
When a tropical cyclone makes landfall or moves into cooler waters, it will dissipate. The cyclone will weaken, the system will become a rain cloud, and the pressure will normalize. This happens because the tropical cyclone no longer has tropical water to feed on. The system simply reverses it's development.