Hurricane – A Tropical Cyclone

A tropical cyclone is a fast-rotating storm system with a low-pressure core, a closed low-level atmospheric circulation, high winds, and a spiral arrangement of thunderstorms causing heavy rain and squalls.

A tropical cyclone is known by several names depending on its location and severity, such as a hurricane, typhoon, tropical storm, cyclonic storm, tropical depression, or simply cyclone.

What is a Hurricane? 

A hurricane is a powerful tropical storm that forms in the Atlantic Ocean or the northeastern Pacific Ocean, whereas a typhoon form in the northwestern Pacific Ocean. In the Indian Ocean, South Pacific, or (rarely) South Atlantic, such storms are referred to simply as "tropical cyclones", while such storms in the Indian Ocean can also be dubbed "strong cyclonic storms".

The term "tropical" alludes to the location of these systems, which originate virtually entirely over tropical oceans. The term "cyclone" alludes to the movement of their winds in a circle, whirling around their central clear eye, with surface winds blowing anticlockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere.

The Coriolis effect causes circulation to flow in the opposite direction. Tropical cyclones often originate over rather warm areas of water. They get their energy from evaporating water from the ocean's surface, which eventually condenses as clouds and rain when wet air rises and cools to saturation.

This energy source is distinct from that of mid-latitude cyclonic storms such as nor'easters and European windstorms, which are predominantly fuelled by horizontal temperature disparities. Tropical cyclones generally have diameters ranging from 100 to 2,000 km (62 to 1,243 mi). Tropical cyclones strike numerous parts of the world every year, including the Gulf Coast of North America, Australia, India, and Bangladesh.

A tropical cyclone's high rotating winds are caused by the conservation of angular momentum given by the Earth's rotation as air rushes inwards toward the axis of rotation. As a result, they almost never occur within 5 degrees of the equator. Tropical cyclones are extremely rare in the South Atlantic (though they do develop on occasion) due to constantly high wind shear and a weak Intertropical Convergence Zone.

The Intensity of Tropical Cyclones

The strength of a tropical cyclone is determined by wind speeds and pressure; connections between wind and pressure are frequently employed in evaluating storm intensity. Tropical cyclone measures, such as the Saffir-Simpson Hurricane Wind Scale and Australia's scale (Bureau of Meteorology), exclusively use wind speed when establishing a storm's category.

Typhoon Tip, which hit the northern Pacific Ocean in 1979, had a minimum pressure of 870 hPa (26 inHg) and maximum sustained wind speeds of 165 km (85 m/s; 306 km/h; 190 mph). Hurricane Patricia in 2015 had the highest maximum sustained wind speed ever recorded at 185 km (95 m/s; 343 km/h; 213 mph)—the most powerful storm ever recorded in the Western Hemisphere.

Factors Influencing Intensity 

Dissipation

A tropical cyclone can weaken, disintegrate, or lose its tropical features in a variety of ways. Making landfall, travelling over cooler water, encountering dry air, or interacting with other weather systems are all examples of these; yet, once a system has dissipated or lost its tropical features, its leftovers may regenerate a tropical cyclone if environmental circumstances improve.

When a tropical cyclone crosses over water that is much colder than 26.5 °C (79.7 °F), it might dissipate. As a result, the storm will lose tropical features such as a warm core with thunderstorms in the centre, and it will become a residual low-pressure region. Remnant systems can exist for several days before being destroyed. This method of dissipation is most frequent in the eastern North Pacific. Weakening or dissipation can also occur when a storm is subjected to vertical wind shear, which causes the convection and heat engine to shift out from the center; this generally stops the development of a tropical cyclone.

Rapid Intensification

On rare occasions, tropical cyclones will experience fast intensification, which is defined as a period in which the maximum sustained winds of a tropical cyclone rise by 30 km (56 km/h; 35 mph) or more within 24 hours. [50] In tropical cyclones, rapid deepening is defined as a minimum sea surface pressure decrease of 1.75 hPa (0.052 inHg) per hour or 42 hPa (1.2 inHg) within a 24-hour period; explosive deepening occurs when the surface pressure decreases by 2.5 hPa (0.074 inHg) per hour for at least 12 hours or 5 hPa (0.15 inHg) per hour for at least 6 hours.  Several criteria must be met for fast intensification to occur.

Water temperatures must be extremely high (around or over 30 °C (86 °F), and the water must be deep enough so that waves do not bring cooler water to the top. Tropical Cyclone Heat Potential, on the other hand, is one of several non-traditional subsurface oceanographic characteristics determining cyclone intensity. Wind shear must be minimal; if the wind shear is severe, the cyclone's convection and circulation will be interrupted.

Formation

Tropical cyclones often form in the summer, although have been observed in virtually every month in the majority of tropical cyclone basins. Tropical cyclones that form on either side of the Equator often form in the Intertropical Convergence Zone, when winds blow from the northeast or southeast.  Air is heated over the warm tropical water and rises in discrete parcels inside this vast area of low pressure, causing thunderous rains to occur.

Several variables, including sea surface temperatures of about 27 °C (81 °F) and minimal vertical wind shear surrounding the system, are necessary for these thunderstorms to develop further.  atmospheric instability, high humidity in the lower to middle troposphere, sufficient Coriolis force to form a low-pressure center, a pre-existing low-level focus or disturbance The severity of a tropical storm is closely connected to the ocean temperatures along its path as well as upper-level divergence.

The time and frequency of tropical storm generation are influenced by climate cycles such as ENSO and the Madden-Julian oscillation. Rossby waves can help a new tropical cyclone emerge by dissipating the energy of an existing, mature storm. Kelvin waves can help tropical cyclones form by influencing the development of westerlies.

Structure 

At the center of a mature tropical cyclone, air sinks rather than rises. For a sufficiently strong storm, air may sink over a layer deep enough to suppress cloud formation, thereby creating a clear "eye". Weather in the eye is normally calm and free of convective clouds, although the sea may be extremely violent. The eye is normally circular and is typically 30–65 km (19–40 mi) in diameter, though eyes as small as 3 km (1.9 mi) and as large as 370 km (230 mi) have been observed.

The "eyewall" refers to the hazy outer margin of the eye. The eyewall often grows outward with height, like an arena football stadium; this phenomenon is referred to as the "stadium effect" at times. The eyewall has the strongest wind speeds, the fastest rising air, the highest cloud altitude, and the heaviest precipitation. Wind damage is most severe when a tropical cyclone's eyewall passes over land.

Movement

The movement of a tropical cyclone (i.e. its "track") is often estimated as the sum of two terms: "steering" by the background ambient wind and "beta drift". Some tropical cyclones may travel enormous distances, such as Hurricane John, the longest-lasting tropical storm on record, which traveled 13,280 km (8,250 mi) throughout its 31-day existence in 1994, the longest track of any Northern Hemisphere tropical cyclone.

Impacts of Tropical Cyclone  

Out at sea, tropical cyclones generate enormous waves, heavy rain, flooding, and high winds, affecting international trade and, in some cases, causing shipwrecks. Tropical cyclones stir up water and leave a chilly wake behind them, making the environment less conducive for future tropical storms. Strong winds on land may damage or destroy automobiles, buildings, bridges, and other external structures, transforming loose material into lethal flying missiles. Storm surge, or the rise in sea level caused by the cyclone, is often the most severe impact of landfalling tropical cyclones, accounting for 90% of tropical cyclone deaths in the past. In March 1899, Cyclone Mahina generated the largest storm surge on record, 13 m (43 ft), near Bathurst Bay, Queensland, Australia.

Rip currents and undertow are two further ocean-based risks caused by tropical cyclones. Even if other meteorological conditions are good, these risks can occur hundreds of kilometers (hundreds of miles) distant from the core of a cyclone. Tornadoes are produced by the extensive rotation of a landfalling tropical storm and the vertical wind shear near its perimeter. Tornadoes can also form as a result of eyewall mesovortices that last till landing. Hurricane Ivan produced the most tornadoes of any tropical storm, with Within tropical cyclones, lightning activity occurs; this activity is more intense within stronger storms and closer to and within the storm's eyewall. Tropical cyclones can enhance the amount of snowfall in a location by bringing in more moisture.

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