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Hurricanes

The loss of much of the British fleet in a hurricane during the Crimean War led to the first international weather-forecasting conference, organized by the American Maury*

An Atlantic hurricane is a type of tropical cyclone that forms in the Atlantic Ocean primarily between June and November. The terms "hurricane", "typhoon", and "cyclone" can be used interchangeably to describe this weather phenomenon. These storms are rotating, organized systems of clouds and thunderstorms that originate over tropical or subtropical waters and have closed low-level circulation. In the North Atlantic, central North Pacific, and eastern North Pacific, the term "hurricane" is mainly used, whereas "typhoon" is more commonly used for storms originating in the Pacific Northwest. The term "cyclone" is used in the South Pacific and Indian Ocean.[1]

Tropical cyclones can be categorized by intensity. Tropical storms have one-minute maximum sustained winds of at least 39 mph (34 knots, 17 m/s, 63 km/h), while hurricanes have one-minute maximum sustained winds exceeding 74 mph (64 knots, 33 m/s, 119 km/h).[2] Most North Atlantic tropical cyclones form between June 1 and November 30.[3] The United States National Hurricane Center monitors tropical weather systems for the North Atlantic Basin and issues reports, watches, and warnings. It is considered to be one of the Regional Specialized Meteorological Centers for tropical cyclones, as defined by the World Meteorological Organization.[4]

Until the mid 1900s, storms were named arbitrarily. From that period on, they were typically given feminine names. The practice of naming storms from a predetermined list began in 1953.[5] Since storm names may be used repeatedly, hurricanes that result in significant damage or casualties may have their names retired from the list at the request of the affected nations to prevent confusion.[6][5] On average, 14 named storms occur each season in the North Atlantic basin, with 7 becoming hurricanes and 3 becoming major hurricanes (Category 3 or greater).[7] The climatological peak of activity is typically around mid-September.[7]

In March 2004, Catarina became the first storm of hurricane strength to be recorded in the South Atlantic Ocean. Since 2011, the Brazilian Navy Hydrographic Center has started to use the same scale as the North Atlantic Ocean for tropical cyclones in the South Atlantic Ocean and assign names to those that reach 35 kn (65 km/h; 40 mph).[8]

Steering factors

The subtropical ridge (in the Pacific) shows up as a large area of black (dryness) on this water vapor satellite image from September 2000

Tropical cyclones are steered by flows surrounding them throughout the depth of the troposphere (the atmospheric layer ranging from the ground to about eight miles (13 km) high). Neil Frank, former director of the United States National Hurricane Center, used analogies such as "a leaf carried along in a stream" or a "brick moving through a river of air" to describe the way atmospheric flow affects the path of a hurricane across the ocean. Specifically, air flow around high pressure systems and toward low-pressure areas influences hurricane tracks.

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Extremes

Costliest Atlantic hurricanes

Hurricane Katrina was the costliest and one of the five deadliest hurricanes in the history of the United States.

Hurricane Harvey was also the costliest hurricane in the history of the United States, causing historic and catastrophic flooding in Texas.

See also: List of Atlantic hurricane records

Atlantic hurricane - Wikipedia

Extra Connections:

Bogart and Bacall starred in the classic, Key Largo. Directed by John Huston, the firm is highlighted Edward G. Robinson as gangster "Johnny Rocco," a seething older synthesis of many of his vicious early bad guy roles. The characters are trapped during a spectacular hurricane in a hotel.

The Great Hurricane of 1780[2][1][3] was the deadliest Atlantic hurricane on record, as well as the deadliest tropical cyclone in the Western Hemisphere. An estimated 22,000 people died throughout the Lesser Antilles when the storm passed through the islands from October 10 to October 16.[4] Specifics on the hurricane's track and strength are unknown, as the official Atlantic hurricane database only goes back to 1851.[5]

The hurricane struck Barbados likely as a Category 5 hurricane, with at least one estimate of wind speeds as high as 200 mph (320 km/h)[6] (greater than any in recorded Atlantic basin history) before moving past Martinique, Saint Lucia, and Sint Eustatius, and causing thousands of deaths on those islands.

Coming in the midst of the American Revolution, the storm caused heavy losses to the British fleet contesting for control of the area, largely weakening British control over the Atlantic.

The hurricane later passed near Puerto Rico and over the eastern portion of Hispaniola, causing heavy damage near the coastlines. It ultimately turned to the northeast and was last observed on October 20 southeast of Atlantic Canada....

The hurricane stripped the bark off trees and left none standing on Barbados.[3] Cuban meteorologist José Carlos Millás has estimated that this damage could be caused only by winds exceeding 200 miles per hour (320 km/h).[9] Every house and fort on Barbados was destroyed. According to British Admiral George Brydges Rodney, the winds carried their heavy cannons aloft 100 feet (30 m).[3]

Great Hurricane of 1780 - Wikipedia

A tropical cyclone is a rapidly rotating storm system characterized by a low-pressure center, a closed low-level atmospheric circulation, strong winds, and a spiral arrangement of thunderstorms that produce heavy rain and squalls. Depending on its location and strength, a tropical cyclone is referred to by different names, including hurricane (/ˈhʌrɪkən, -keɪn/), typhoon (/taɪˈfuːn/), tropical storm, cyclonic storm, tropical depression, or simply cyclone. A hurricane is a strong tropical cyclone that occurs in the Atlantic Ocean or northeastern Pacific Ocean, and a typhoon occurs in the northwestern Pacific Ocean. In the Indian Ocean and South Pacific, comparable storms are referred to as "tropical cyclones", and such storms in the Indian Ocean can also be called "severe cyclonic storms".

"Tropical" refers to the geographical origin of these systems, which form almost exclusively over tropical seas. "Cyclone" refers to their winds moving in a circle, whirling round their central clear eye, with their surface winds blowing counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere.

The opposite direction of circulation is due to the Coriolis effect. 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 condenses 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 powered primarily by horizontal temperature contrasts. Tropical cyclones are typically between 100 and 2,000 km (62 and 1,243 mi) in diameter. Every year tropical cyclones affect various regions of the globe including the Gulf Coast of North America, Australia, India, and Bangladesh.

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 very rare in the South Atlantic (although occasional examples do occur) due to consistently strong wind shear and a weak Intertropical Convergence Zone. Conversely, the African easterly jet and areas of atmospheric instability give rise to cyclones in the Atlantic Ocean and Caribbean Sea, while cyclones near Australia owe their genesis to the Asian monsoon and Western Pacific Warm Pool.

The primary energy source for these storms is warm ocean waters. These storms are therefore typically strongest when over or near water, and they weaken quite rapidly over land. This causes coastal regions to be particularly vulnerable to tropical cyclones, compared to inland regions. Coastal damage may be caused by strong winds and rain, high waves (due to winds), storm surges (due to wind and severe pressure changes), and the potential of spawning tornadoes.

Tropical cyclones draw in air from a large area and concentrate the water content of that air (from atmospheric moisture and moisture evaporated from water) into precipitation over a much smaller area. This replenishing of moisture-bearing air after rain may cause multi-hour or multi-day extremely heavy rain up to 40 km (25 mi) from the coastline, far beyond the amount of water that the local atmosphere holds at any one time. This in turn can lead to river flooding, overland flooding, and a general overwhelming of local water control structures across a large area. Although their effects on human populations can be devastating, tropical cyclones may play a role in relieving drought conditions, though this claim is disputed. They also carry heat and energy away from the tropics and transport it towards temperate latitudes, which plays an important role in regulating global climate.

Background

A tropical cyclone is the generic term for a warm-cored, non-frontal synoptic-scale low-pressure system over tropical or subtropical waters around the world.[1][2] The systems generally have a well-defined center which is surrounded by deep atmospheric convection and a closed wind circulation at the surface.[1]

Historically, tropical cyclones have occurred around the world for thousands of years, with one of the earliest tropical cyclones on record estimated to have occurred in Western Australia in around 4000 BC.[3] However, before satellite imagery became available during the 20th century, there was no way to detect a tropical cyclone unless it impacted land or a ship encountered it by chance.[4]

In modern times, on average around 80 to 90 named tropical cyclones form each year around the world, over half of which develop hurricane-force winds of 65 kn (120 km/h; 75 mph) or more.[4] Around the world, a tropical cyclone is generally deemed to have formed once mean surface winds in excess of 35 kn (65 km/h; 40 mph) are observed.[4] It is assumed at this stage that a tropical cyclone has become self-sustaining and can continue to intensify without any help from its environment.[4]

A study review article published in 2021 in Nature Geoscience concluded that the geographic range of tropical cyclones will probably expand poleward in response to climate warming of the Hadley circulation.[5]

Intensity

Tropical cyclone intensity is based on wind speeds and pressure; relationships between winds and pressure are often used in determining the intensity of a storm.[6] Tropical cyclone scales such as the Saffir-Simpson Hurricane Wind Scale and Australia's scale (Bureau of Meteorology) only use wind speed for determining the category of a storm.[7][8] The most intense storm on record is Typhoon Tip in the northwestern Pacific Ocean in 1979, which reached a minimum pressure of 870 hPa (26 inHg) and maximum sustained wind speeds of 165 kn (85 m/s; 305 km/h; 190 mph).[9] The highest maximum sustained wind speed ever recorded was 185 kn (95 m/s; 345 km/h; 215 mph) in Hurricane Patricia in 2015—the most intense cyclone ever recorded in the Western Hemisphere.[10]

Factors that influence intensity

Warm sea surface temperatures are required in order for tropical cyclones to form and strengthen. The commonly-accepted minimum temperature range for this to occur is 26–27 °C (79–81 °F), however, multiple studies have proposed a lower minimum of 25.5 °C (77.9 °F).[11][12] Higher sea surface temperatures result in faster intensification rates and sometimes even rapid intensification.[13] High ocean heat content, also known as Tropical Cyclone Heat Potential, allows storms to achieve a higher intensity.[14] Most tropical cyclones that experience rapid intensification are traversing regions of high ocean heat content rather than lower values.[15] High ocean heat content values can help to offset the oceanic cooling caused by the passage of a tropical cyclone, limiting the effect this cooling has on the storm.[16] Faster-moving systems are able to intensify to higher intensities with lower ocean heat content values. Slower-moving systems require higher values of ocean heat content to achieve the same intensity.[15]

The passage of a tropical cyclone over the ocean causes the upper layers of the ocean to cool substantially, a process known as upwelling,[17] which can negatively influence subsequent cyclone development. This cooling is primarily caused by wind-driven mixing of cold water from deeper in the ocean with the warm surface waters. This effect results in a negative feedback process that can inhibit further development or lead to weakening. Additional cooling may come in the form of cold water from falling raindrops (this is because the atmosphere is cooler at higher altitudes). Cloud cover may also play a role in cooling the ocean, by shielding the ocean surface from direct sunlight before and slightly after the storm passage. All these effects can combine to produce a dramatic drop in sea surface temperature over a large area in just a few days.[18] Conversely, the mixing of the sea can result in heat being inserted in deeper waters, with potential effects on global climate.[19]

Vertical wind shear negatively affects tropical cyclone intensification by displacing moisture and heat from a system's center.[20] Low levels of vertical wind shear are most optimal for strengthening, while stronger wind shear induces weakening.[21][22] Dry air entraining into a tropical cyclone's core has a negative effect on its development and intensity by diminishing atmospheric convection and introducing asymmetries in the storm's structure.[23][24][25] Symmetric, strong outflow leads to a faster rate of intensification than observed in other systems by mitigating local wind shear.[26][27][28] Weakening outflow is associated with the weakening of rainbands within a tropical cyclone.[29]

The size of tropical cyclones plays a role in how quickly they intensify. Smaller tropical cyclones are more prone to rapid intensification than larger ones.[30] The Fujiwhara effect, which involves interaction between two tropical cyclones, can weaken and ultimately result in the dissipation of the weaker of two tropical cyclones by reducing the organization of the system's convection and imparting horizontal wind shear.[31] Tropical cyclones typically weaken while situated over a landmass because conditions are often unfavorable as a result of the lack of oceanic forcing.[32]

The Brown ocean effect can allow a tropical cyclone to maintain or increase its intensity following landfall, in cases where there has been copious rainfall, through the release of latent heat from the saturated soil.[33] Orographic lift can cause an significant increase in the intensity of the convection of a tropical cyclone when its eye moves over a mountain, breaking the capped boundary layer that had been restraining it.[34] Jet streams can both enhance and inhibit tropical cyclone intensity by influencing the storm's outflow as well as vertical wind shear.[35][36]

Formation

Main article: Tropical cyclogenesis

Diagram of a tropical cyclone in the Northern Hemisphere

Tropical cyclones tend to develop during the summer, but have been noted in nearly every month in most tropical cyclone basins. Tropical cyclones on either side of the Equator generally have their origins in the Intertropical Convergence Zone, where winds blow from either the northeast or southeast.[37] Within this broad area of low-pressure, air is heated over the warm tropical ocean and rises in discrete parcels, which causes thundery showers to form.[37] These showers dissipate quite quickly; however, they can group together into large clusters of thunderstorms.[37] This creates a flow of warm, moist, rapidly rising air, which starts to rotate cyclonically as it interacts with the rotation of the earth.[37]

Several factors are required for these thunderstorms to develop further, including sea surface temperatures of around 27 °C (81 °F) and low vertical wind shear surrounding the system,[37][38] atmospheric instability, high humidity in the lower to middle levels of the troposphere, enough Coriolis force to develop a low-pressure center, and a pre-existing low-level focus or disturbance.[38] There is a limit on tropical cyclone intensity which is strongly related to the water temperatures along its path.[39] and upper-level divergence.[40] An average of 86 tropical cyclones of tropical storm intensity form annually worldwide. Of those, 47 reach strength higher than 119 km/h (74 mph), and 20 become intense tropical cyclones (at least Category 3 intensity on the Saffir–Simpson scale).[41]

Climate cycles such as ENSO and the Madden–Julian oscillation modulate the timing and frequency of tropical cyclone development.[42][43][44][45] Rossby waves can aid in the formation of a new tropical cyclone by disseminating the energy of an existing, mature storm.[46][47] Kelvin waves can contribute to tropical cyclone formation by regulating the development of the westerlies.[48] Cyclone formation is usually reduced 3 days prior to the wave's crest and increased during the 3 days after.[49]

Rapid intensification

Main article: Rapid intensification

On occasion, tropical cyclones may undergo a process known as rapid intensification, a period in which the maximum sustained winds of a tropical cyclone increase by 30 kn (56 km/h; 35 mph) or more within 24 hours.[50] Similarly, rapid deepening in tropical cyclones 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.[51]

For rapid intensification to occur, several conditions must be in place. Water temperatures must be extremely high (near or above 30 °C (86 °F)), and water of this temperature must be sufficiently deep such that waves do not upwell cooler waters to the surface. On the other hand, Tropical Cyclone Heat Potential is one of such non-conventional subsurface oceanographic parameters influencing the cyclone intensity. Wind shear must be low; when wind shear is high, the convection and circulation in the cyclone will be disrupted. Usually, an anticyclone in the upper layers of the troposphere above the storm must be present as well—for extremely low surface pressures to develop, air must be rising very rapidly in the eyewall of the storm, and an upper-level anticyclone helps channel this air away from the cyclone efficiently.[52] However, some cyclones such as Hurricane Epsilon have rapidly intensified despite relatively unfavorable conditions.[53][54]

Dissipation

Hurricane Paulette, in 2020, is an example of a sheared tropical cyclone, with deep convection slightly removed from the center of the system.

There are a number of ways a tropical cyclone can weaken, dissipate, or lose its tropical characteristics. These include making landfall, moving over cooler water, encountering dry air, or interacting with other weather systems; however, once a system has dissipated or lost its tropical characteristics, its remnants could regenerate a tropical cyclone if environmental conditions become favorable.[55][56]

A tropical cyclone can dissipate when it moves over waters significantly cooler than 26.5 °C (79.7 °F). This will deprive the storm of such tropical characteristics as a warm core with thunderstorms near the center, so that it becomes a remnant low-pressure area. Remnant systems may persist for several days before losing their identity. This dissipation mechanism is most common in the eastern North Pacific. Weakening or dissipation can also occur if a storm experiences vertical wind shear which causes the convection and heat engine to move away from the center; this normally ceases the development of a tropical cyclone.[57] In addition, its interaction with the main belt of the Westerlies, by means of merging with a nearby frontal zone, can cause tropical cyclones to evolve into extratropical cyclones. This transition can take 1–3 days.[58]

Should a tropical cyclone make landfall or pass over an island, its circulation could start to break down, especially if it encounters mountainous terrain.[59] When a system makes landfall on a large landmass, it is cut off from its supply of warm moist maritime air and starts to draw in dry continental air.[59] This, combined with the increased friction over land areas, leads to the weakening and dissipation of the tropical cyclone.[59] Over a mountainous terrain, a system can quickly weaken; however, over flat areas, it may endure for two to three days before circulation breaks down and dissipates.[59]

Over the years, there have been a number of techniques considered to try to artificially modify tropical cyclones.[60] These techniques have included using nuclear weapons, cooling the ocean with icebergs, blowing the storm away from land with giant fans, and seeding selected storms with dry ice or silver iodide.[60] These techniques, however, fail to appreciate the duration, intensity, power or size of tropical cyclones.[60]...

Tropical cyclone - Wikipedia