154-417: Hurricane Sally was a destructive and slow-moving tropical cyclone that was the first hurricane to make landfall in the U.S. state of Alabama since Ivan in 2004 , coincidentally on the same date in the same place. The eighteenth named storm and seventh hurricane of the extremely active 2020 Atlantic hurricane season , Sally developed from an area of disturbed weather which was first monitored over
308-531: A Tropical Cyclone Warning Centre by the World Meteorological Organization 's (WMO) tropical cyclone programme. These warning centers issue advisories which provide basic information and cover a systems present, forecast position, movement and intensity, in their designated areas of responsibility. Meteorological services around the world are generally responsible for issuing warnings for their own country. There are exceptions, as
462-416: A 1.5 degree warming lead to "increased proportion of and peak wind speeds of intense tropical cyclones". We can say with medium confidence that regional impacts of further warming include more intense tropical cyclones and/or extratropical storms. Climate change can affect tropical cyclones in a variety of ways: an intensification of rainfall and wind speed, a decrease in overall frequency, an increase in
616-444: A 2019 review paper show a future increase of rainfall rates. Additional sea level rise will increase storm surge levels. It is plausible that extreme wind waves see an increase as a consequence of changes in tropical cyclones, further exacerbating storm surge dangers to coastal communities. The compounding effects from floods, storm surge, and terrestrial flooding (rivers) are projected to increase due to global warming . There
770-610: A 27-year-old boater went missing when he left his home in a 12-foot jon , in an attempt to find his mother's pontoon boat that became untethered in the strong currents and whipping winds brought on by the hurricane; one week after his disappearance, his body was found washed ashore near the Blue Angel Recreation Park. Another person in Pensacola also died after succumbing to carbon monoxide poisoning from indoor generator use. The body of another missing boater,
924-902: A 45-year-old female kayaker who had also gone missing at the height of the storm, was discovered, marking the third fatality of Pensacola and the state of Florida. The Shoal River in Okaloosa county saw its highest level in 20 years as a result of all the rain that fell from Sally. This resulted in parts of Crestview, Florida being evacuated and bridges on I-10 and SR 85 being closed to all traffic. Damage in Florida totaled to $ 180.113 million. Continuous onshore flow from Sally caused storm surge flooding to occur on Dauphin Island beginning early on September 14. Two unoccupied riverboat casinos in Bayou La Batre near Mobile broke loose due to
1078-502: A brief period of rapid intensification . Its winds increased to 85 mph (140 km/h) by 18:00 UTC at the end of this phase, constituting its initial peak intensity. Nearby land-based Doppler weather radar depicted a developing mid- to upper-level eye within the hurricane's core at this time. The northern outer bands of the hurricane began impacting the Florida Panhandle early on September 14, primarily along
1232-613: 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 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
1386-579: A decaying frontal boundary and led to the development of Tropical Storm Omar . This weak tropical cyclone later became embedded within a broad mid-level trough well to the north of Bermuda as it dissipated on September 5; an extension of this trough propagated southwest as Omar moved over the North Atlantic. Over the next five days, the system remained disorganized as it approached the Bahamas . The National Hurricane Center (NHC) first noted
1540-487: A few kilometers before dissipating. Some attain wind speeds in excess of 480 kilometres per hour (300 mph), may stretch more than a 1.6 kilometres (0.99 mi) across, and maintain contact with the ground for more than 100 kilometres (62 mi). Tornadoes, despite being one of the most destructive weather phenomena, are generally short-lived. A long-lived tornado generally lasts no more than an hour, but some have been known to last for 2 hours or longer (for example,
1694-405: A flow of warm, moist, rapidly rising air, which starts to rotate cyclonically as it interacts with the rotation of the earth. 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, atmospheric instability, high humidity in the lower to middle levels of
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#17327724188911848-495: A frontal boundary over Georgia six hours later, and a defined warm front became established to the east-northeast. The trailing surface circulation of Sally continued to weaken before dissipating over South Carolina on September 18. A new low-pressure area developed over eastern North Carolina later that day in association with the aforementioned front and Sally's remnants. A convergence zone developed across northern North Carolina into southeastern Virginia as warm, moist air from
2002-506: A higher intensity. Most tropical cyclones that experience rapid intensification are traversing regions of high ocean heat content rather than lower values. 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. 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
2156-464: A large number of forecasting centers, uses infrared geostationary satellite imagery and an algorithm based upon the Dvorak technique to assess the intensity of tropical cyclones. The ADT has a number of differences from the conventional Dvorak technique, including changes to intensity constraint rules and the usage of microwave imagery to base a system's intensity upon its internal structure, which prevents
2310-768: A large oak tree fell onto two homes and several cars in Atlanta . Two other fatalities occurred in metro Atlanta , one in Cobb County where a man died after a slick road caused a driver to lose control of his vehicle and hit the bus stop where the man was waiting at, and another in Gwinnett County where a 71-year-old woman was killed when a tree fell across the roadway, pinning her underneath it. In North Carolina and South Carolina , 16 more tornadoes were also confirmed from September 17–18. Two of them were rated EF1 and two others were rated EFU, while all
2464-464: A large role in both the classification of a tropical cyclone and the determination of its intensity. Used in warning centers, the method was developed by Vernon Dvorak in the 1970s, and uses both visible and infrared satellite imagery in the assessment of tropical cyclone intensity. The Dvorak technique uses a scale of "T-numbers", scaling in increments of 0.5 from T1.0 to T8.0. Each T-number has an intensity assigned to it, with larger T-numbers indicating
2618-507: A lifting force (heat). All thunderstorms , regardless of type, go through three stages: the developing stage , the mature stage , and the dissipation stage . The average thunderstorm has a 24 km (15 mi) diameter. Depending on the conditions present in the atmosphere, these three stages take an average of 30 minutes to go through. There are four main types of thunderstorms: single-cell, multicell, squall line (also called multicell line), and supercell. Which type forms depends on
2772-400: A liquid phase. Undergoing "wet growth", the outer layer is sticky , or more adhesive, so a single hailstone may grow by collision with other smaller hailstones, forming a larger entity with an irregular shape. The hailstone will keep rising in the thunderstorm until its mass can no longer be supported by the updraft. This may take at least 30 minutes based on the force of the updrafts in
2926-507: A minimum central pressure of 965 millibars (28.5 inHg). The storm rapidly weakened after landfall before transitioning into an extratropical low at 12:00 UTC the next day. Sally's remnants lasted for another day as they moved off the coast of the Southeastern United States before being absorbed into another extratropical storm on September 18. Numerous watches and warnings were issued in anticipation of
3080-573: A minimum pressure of 965 mbar (hPa; 28.49 inHg). This coincidentally occurred on the 16th anniversary of Hurricane Ivan 's landfall in the same location and just three hours later. Ingram Bayou saw the most intense winds, with sustained values reaching 113 mph (182 km/h) and a peak gust of 137 mph (220 km/h). These were observed atop an 59 ft (18 m) mast and were not representative of surface values. Hurricane Sally's structure rapidly degraded as it progressed farther inland throughout September 16. Briefly crossing
3234-426: 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. A tropical cyclone
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#17327724188913388-640: A news conference that 103,000 customers were still without power in Baldwin County, and another 60,000 in Mobile County. Five days after landfall, Baldwin EMC had restored power to close to 60,000 meters, representing 75% of their subscribers, but 18,197 meters remained without power. Total damages in Alabama reached $ 311.895 million (2020 USD ). The winds from the outer bands of Sally caused
3542-416: A number of other weather conditions. A few examples on the smaller scale would include: Convection mixing the planetary boundary layer (PBL) and allowing drier air aloft to the surface thereby decreasing dew points, creating cumulus-type clouds that can limit a small amount of sunshine, increasing surface winds, making outflow boundaries/and other smaller boundaries more diffuse, and the eastward propagation of
3696-493: A number of techniques considered to try to artificially modify tropical cyclones. 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 . These techniques, however, fail to appreciate the duration, intensity, power or size of tropical cyclones. A variety of methods or techniques, including surface, satellite, and aerial, are used to assess
3850-422: 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. 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
4004-429: 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. In addition, its interaction with
4158-473: A speed that is relatively low to what one finds in a thunderstorm updraft. Because of this, it is not the actual air being pushed to its LFC that "breaks through" the inhibition, but rather the forcing cools the inhibition adiabatically. This would counter, or "erode" the increase of temperature with height that is present during a capping inversion. Forcing mechanisms that can lead to the eroding of inhibition are ones that create some sort of evacuation of mass in
4312-569: A storm. 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. 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). The highest maximum sustained wind speed ever recorded
4466-581: A stronger system. Tropical cyclones are assessed by forecasters according to an array of patterns, including curved banding features , shear, central dense overcast, and eye, to determine the T-number and thus assess the intensity of the storm. The Cooperative Institute for Meteorological Satellite Studies works to develop and improve automated satellite methods, such as the Advanced Dvorak Technique (ADT) and SATCON. The ADT, used by
4620-405: A system has dissipated or lost its tropical characteristics, its remnants could regenerate a tropical cyclone if environmental conditions become favorable. 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
4774-529: 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, cyclones 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 . In contrast,
Hurricane Sally - Misplaced Pages Continue
4928-461: 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. Symmetric, strong outflow leads to a faster rate of intensification than observed in other systems by mitigating local wind shear. Weakening outflow is associated with the weakening of rainbands within a tropical cyclone. Tropical cyclones may still intensify, even rapidly, in
5082-401: A tropical cyclone's intensity or the direction it is traveling. Wind-pressure relationships (WPRs) are used as a way to determine the pressure of a storm based on its wind speed. Several different methods and equations have been proposed to calculate WPRs. Tropical cyclones agencies each use their own, fixed WPR, which can result in inaccuracies between agencies that are issuing estimates on
5236-578: A two-digit number and suffix letter by the warning centers that monitor them. Atmospheric convection Atmospheric convection is the result of a parcel -environment instability (temperature difference layer) in the atmosphere. Different lapse rates within dry and moist air masses lead to instability. Mixing of air during the day expands the height of the planetary boundary layer , leading to increased winds, cumulus cloud development, and decreased surface dew points . Convection involving moist air masses leads to thunderstorm development, which
5390-831: A typhoon. This happened in 2014 for Hurricane Genevieve , which became Typhoon Genevieve. Within the Southern Hemisphere, it is either called a hurricane, tropical cyclone or a severe tropical cyclone, depending on if it is located within the South Atlantic, South-West Indian Ocean, Australian region or the South Pacific Ocean. The descriptors for tropical cyclones with wind speeds below 65 kn (120 km/h; 75 mph) vary by tropical cyclone basin and may be further subdivided into categories such as "tropical storm", "cyclonic storm", "tropical depression", or "deep depression". The practice of using given names to identify tropical cyclones dates back to
5544-696: Is a strong tropical cyclone that occurs in the Atlantic Ocean or northeastern Pacific Ocean . A typhoon occurs in the northwestern Pacific Ocean. In the Indian Ocean and South Pacific, comparable storms are referred to as "tropical cyclones". 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. Tropical cyclones typically form over large bodies of relatively warm water. They derive their energy through
5698-419: Is another factor in the hailstone's growth. When the hailstone moves into an area with a high concentration of water droplets, it captures the latter and acquires a translucent layer. Should the hailstone move into an area where mostly water vapour is available, it acquires a layer of opaque white ice. Furthermore, the hailstone's speed depends on its position in the cloud's updraft and its mass. This determines
5852-519: Is applied to damage from microbursts. Downbursts are particularly strong downdrafts from thunderstorms. Downbursts in air that is precipitation free or contains virga are known as dry downbursts ; those accompanied with precipitation are known as wet downbursts . Most downbursts are less than 4 kilometres (2.5 mi) in extent: these are called microbursts . Downbursts larger than 4 kilometres (2.5 mi) in extent are sometimes called macrobursts . Downbursts can occur over large areas. In
6006-415: Is assumed at this stage that a tropical cyclone has become self-sustaining and can continue to intensify without any help from its environment. Depending on its location and strength, a tropical cyclone is referred to by different names , including hurricane , typhoon , tropical storm , cyclonic storm , tropical depression , or simply cyclone . A hurricane is a strong tropical cyclone that occurs in
6160-402: Is because the physical properties of a downburst are completely different from those of a tornado. Downburst damage will radiate from a central point as the descending column spreads out when impacting the surface, whereas tornado damage tends towards convergent damage consistent with rotating winds. To differentiate between tornado damage and damage from a downburst, the term straight-line winds
6314-406: Is calculated as: where p {\textstyle p} is the density of air, u {\textstyle u} is a sustained surface wind speed value, and d v {\textstyle d_{v}} is the volume element . Around the world, tropical cyclones are classified in different ways, based on the location ( tropical cyclone basins ), the structure of
Hurricane Sally - Misplaced Pages Continue
6468-444: Is caused by colder air being displaced at the top of the thermal. Another convection-driven weather effect is the sea breeze . Warm air has a lower density than cool air, so warm air rises within cooler air, similar to hot air balloons . Clouds form as relatively warmer air carrying moisture rises within cooler air. As the moist air rises, it cools causing some of the water vapor in the rising packet of air to condense . When
6622-554: Is currently no consensus on how climate change will affect the overall frequency of tropical cyclones. A majority of climate models show a decreased frequency in future projections. For instance, a 2020 paper comparing nine high-resolution climate models found robust decreases in frequency in the Southern Indian Ocean and the Southern Hemisphere more generally, while finding mixed signals for Northern Hemisphere tropical cyclones. Observations have shown little change in
6776-414: Is cut off from its supply of warm moist maritime air and starts to draw in dry continental air. This, combined with the increased friction over land areas, leads to the weakening and dissipation of the tropical cyclone. Over a mountainous terrain, a system can quickly weaken. Over flat areas, it may endure for two to three days before circulation breaks down and dissipates. Over the years, there have been
6930-520: Is in a multicellular thunderstorm where the hailstone may be ejected from the top of the "mother" cell and captured in the updraft of a more intense "daughter cell". This however is an exceptional case. A downburst is created by a column of sinking air that, after hitting ground level, spreads out in all directions and is capable of producing damaging straight-line winds of over 240 kilometres per hour (150 mph), often producing damage similar to, but distinguishable from, that caused by tornadoes . This
7084-457: Is largely absent in winter midlatitudes. Its counterpart in the ocean (deep convection downward in the water column) only occurs at a few locations. A thermal column (or thermal) is a vertical section of rising air in the lower altitudes of the Earth's atmosphere. Thermals are created by the uneven heating of the Earth's surface from solar radiation. The Sun warms the ground, which in turn warms
7238-417: Is made of thick and translucent layers, alternating with layers that are thin, white, and opaque. Former theory suggested that hailstones were subjected to multiple descents and ascents, falling into a zone of humidity and refreezing as they were uplifted. This up-and-down motion was thought to be responsible for the successive layers of the hailstone. New research (based on theory and field study) has shown this
7392-481: Is not necessarily true. The storm's updraft , with upwardly directed wind speeds as high as 180 kilometres per hour (110 mph), blow the forming hailstones up the cloud. As the hailstone ascends it passes into areas of the cloud where the concentration of humidity and supercooled water droplets varies. The hailstone's growth rate changes depending on the variation in humidity and supercooled water droplets that it encounters. The accretion rate of these water droplets
7546-409: Is often displayed on a Skew-T chart or other similar thermodynamic diagram. These can be plotted by a measured sounding analysis , which is the sending of a radiosonde attached to a balloon into the atmosphere to take the measurements with height. Forecast models can also create these diagrams, but are less accurate due to model uncertainties and biases, and have lower spatial resolution. Although,
7700-412: Is often responsible for severe weather throughout the world. Special threats from thunderstorms include hail , downbursts , and tornadoes . There are a few general archetypes of atmospheric instability that are used to explain convection (or lack thereof); a necessary but insufficient condition for convection is that the environmental lapse rate (the rate of decrease of temperature with height)
7854-424: Is one situation where forcing mechanisms provide support for very steep environmental lapse rates, which as mentioned before is an archetype for favored convection. The small amount of latent heat released from air rising and condensing moisture in a thundersnow also serves to increase this convective potential, although minimally. There are also three types of thunderstorms: orographic, air mass, and frontal. Despite
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#17327724188918008-428: Is steeper than the lapse rate experienced by a rising parcel of air. When this condition is met, upward-displaced air parcels can become buoyant and thus experience a further upward force. Buoyant convection begins at the level of free convection (LFC) , above which an air parcel may ascend through the free convective layer (FCL) with positive buoyancy. Its buoyancy turns negative at the equilibrium level (EL) , but
8162-445: Is the generic term for a warm-cored, non-frontal synoptic-scale low-pressure system over tropical or subtropical waters around the world. The systems generally have a well-defined center which is surrounded by deep atmospheric convection and a closed wind circulation at the surface. 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. It
8316-512: Is the greatest. However, each particular basin has its own seasonal patterns. On a worldwide scale, May is the least active month, while September is the most active month. November is the only month in which all the tropical cyclone basins are in season. In the Northern Atlantic Ocean , a distinct cyclone season occurs from June 1 to November 30, sharply peaking from late August through September. The statistical peak of
8470-405: Is the storm's wind speed and r {\textstyle r} is the radius of hurricane-force winds. The Hurricane Severity Index is a scale that can assign up to 50 points to a system; up to 25 points come from intensity, while the other 25 come from the size of the storm's wind field. The IKE model measures the destructive capability of a tropical cyclone via winds, waves, and surge. It
8624-486: Is the strongest of the thunderstorms, most commonly associated with large hail, high winds, and tornado formation. The latent heat release from condensation is the determinant between significant convection and almost no convection at all. The fact that air is generally cooler during winter months, and therefore cannot hold as much water vapor and associated latent heat, is why significant convection (thunderstorms) are infrequent in cooler areas during that period. Thundersnow
8778-620: The African easterly jet and areas of atmospheric instability give rise to cyclones in the Atlantic Ocean and Caribbean Sea . Heat energy from the ocean acts as the accelerator for tropical cyclones. This causes inland regions to suffer far less damage from cyclones than coastal regions, although the impacts of flooding are felt across the board. 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
8932-513: 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
9086-772: The Florida coast due to possible waterspouts. An EF0 tornado south of Marianna damaged a shed and uprooted several trees on September 16. Sally caused heavy rainfall and moderate flooding in South Florida and the Florida Keys , with nearly 8.5 inches (220 mm) falling over Marathon , over 10 inches (250 mm) in Key West and peaking at 12 inches (300 mm) in Lower Matecumbe Key . Tropical storm-force gusts were reported in portions of
9240-412: The Florida Keys and Florida Bay while producing heavy rainfall in the region. As Sally rounded the southern edge of the ridge and turned west-northwest, modest wind shear inhibited significant intensification over the next day. A prominent central dense overcast , displaced about 50–60 mi (85–95 km) from the circulation center, blossomed early on September 13. A convergence zone along
9394-688: The Gulf Breeze , causing the city to shut off water from the south side of Highway 98 inside city limits, where the majority of water main breaks occurred in order to isolate the leaks. Water main break also occurred in nearby Pensacola Beach , causing officials to advise residents to fill their bathtubs with water. The city of Panama City reported releases of raw sewage from several locations due to flooding from Hurricane Sally, prompting The Florida Department of Health to issue advises against swimming in Panama City until further notice. In Pensacola,
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#17327724188919548-647: The Hurricane Surge Index , the Hurricane Severity Index , the Power Dissipation Index (PDI), and integrated kinetic energy (IKE). ACE is a metric of the total energy a system has exerted over its lifespan. ACE is calculated by summing the squares of a cyclone's sustained wind speed, every six hours as long as the system is at or above tropical storm intensity and either tropical or subtropical. The calculation of
9702-559: The Madden–Julian oscillation . The IPCC Sixth Assessment Report summarize the latest scientific findings about the impact of climate change on tropical cyclones. According to the report, we have now better understanding about the impact of climate change on tropical storm than before. Major tropical storms likely became more frequent in the last 40 years. We can say with high confidence that climate change increase rainfall during tropical cyclones. We can say with high confidence that
9856-534: The Miami metropolitan area . The Panhandle area east of where Sally made landfall suffered the brunt of the storm in Florida. In Escambia County , which includes Pensacola , the sheriff kept police deputies out helping residents "as long as physically possible". In Santa Rosa County , the City of Gulf Breeze was impacted with widespread wind damage, storm surge flooding, and over 20 inches (510 mm) of rainfall in
10010-460: The Saffir–Simpson scale . Climate oscillations such as El Niño–Southern Oscillation (ENSO) and the Madden–Julian oscillation modulate the timing and frequency of tropical cyclone development. Rossby waves can aid in the formation of a new tropical cyclone by disseminating the energy of an existing, mature storm. Kelvin waves can contribute to tropical cyclone formation by regulating
10164-511: The Saffir–Simpson scale . The trend was most clear in the North Atlantic and in the Southern Indian Ocean. In the North Pacific, tropical cyclones have been moving poleward into colder waters and there was no increase in intensity over this period. With 2 °C (3.6 °F) warming, a greater percentage (+13%) of tropical cyclones are expected to reach Category 4 and 5 strength. A 2019 study indicates that climate change has been driving
10318-495: The Tri-state tornado ). Due to their relatively short duration, less information is known about the development and formation of tornadoes. Generally any cyclone based on its size and intensity has different instability dynamics. The most unstable azimuthal wavenumber is higher for bigger cyclones . The potential for convection in the atmosphere is often measured by an atmospheric temperature/dewpoint profile with height. This
10472-514: The troposphere , enough Coriolis force to develop a low-pressure center , and a pre-existing low-level focus or disturbance. There is a limit on tropical cyclone intensity which is strongly related to the water temperatures along its path. and upper-level divergence. 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, of at least Category 3 intensity on
10626-640: The Atlantic hurricane season is September 10. The Northeast Pacific Ocean has a broader period of activity, but in a similar time frame to the Atlantic. The Northwest Pacific sees tropical cyclones year-round, with a minimum in February and March and a peak in early September. In the North Indian basin, storms are most common from April to December, with peaks in May and November. In the Southern Hemisphere,
10780-431: The Bahamas on September 10. The system grew a broad area of low-pressure on September 11, and was designated as a tropical depression late that day. Early the next day, the depression made landfall at Key Biscayne and subsequently strengthened into Tropical Storm Sally that afternoon. Moderate northwesterly shear prevented significant intensification for the first two days, but convection continued to grow towards
10934-499: The Baptist Parish . Shelters were opened while public school and university classes were canceled throughout southeastern Louisiana for September 15. FEMA declared that they will be bringing additional resources to Louisiana for the storm's aftermath and not diverting resources away from Hurricane Laura 's relief efforts. Lakeshore Drive along Lake Pontchartrain was closed before the storm as well. A state of emergency
11088-471: The CAPE is sometimes called a thermodynamic speed limit for updrafts, based on the simple kinetic energy equation . However, such buoyant acceleration concepts give an oversimplified view of convection. Drag is an opposite force to counter buoyancy, so that parcel ascent occurs under a balance of forces, like the terminal velocity of a falling object. Buoyancy may be reduced by entrainment , which dilutes
11242-556: The Equator generally have their origins in the Intertropical Convergence Zone , where winds blow from either the northeast or southeast. 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. These showers dissipate quite quickly; however, they can group together into large clusters of thunderstorms. This creates
11396-783: The Gulf Shores with a few being destroyed. Meanwhile, in Downtown Mobile, a street light snapped, swinging wildly on its cable. A gas station was destroyed in Spanish Fort, Alabama . Several sewage overflows were reported across Mobile County following heavy rain from Hurricane Sally, causing contamination to Dog River and Rabbit Creek. One person was declared dead and one other missing in Orange Beach , an area most impacted by flooding. Another person died in Foley during
11550-632: The PDI is similar in nature to ACE, with the major difference being that wind speeds are cubed rather than squared. The Hurricane Surge Index is a metric of the potential damage a storm may inflict via storm surge. It is calculated by squaring the dividend of the storm's wind speed and a climatological value (33 m/s or 74 mph), and then multiplying that quantity by the dividend of the radius of hurricane-force winds and its climatological value (96.6 km or 60.0 mi). This can be represented in equation form as: where v {\textstyle v}
11704-463: The South Atlantic is not a major basin, and not an official basin according to the WMO. Each year on average, around 80 to 90 named tropical cyclones form around the world, of which over half develop hurricane-force winds of 65 kn (120 km/h; 75 mph) or more. Worldwide, tropical cyclone activity peaks in late summer, when the difference between temperatures aloft and sea surface temperatures
11858-610: The United States National Hurricane Center and Fiji Meteorological Service issue alerts, watches and warnings for various island nations in their areas of responsibility. The United States Joint Typhoon Warning Center and Fleet Weather Center also publicly issue warnings about tropical cyclones on behalf of the United States Government . The Brazilian Navy Hydrographic Center names South Atlantic tropical cyclones , however
12012-591: The Western Pacific. Tropical cyclones have to have a significant amount of gale-force winds occurring around the center before they are named within the Southern Hemisphere . The names of significant tropical cyclones in the North Atlantic Ocean, Pacific Ocean, and Australian region are retired from the naming lists and replaced with another name. Tropical cyclones that develop around the world are assigned an identification code consisting of
12166-433: The air directly above it. The warmer air expands, becoming less dense than the surrounding air mass, and creating a thermal low . The mass of lighter air rises, and as it does, it cools due to its expansion at lower high-altitude pressures. It stops rising when it has cooled to the same temperature as the surrounding air. Associated with a thermal is a downward flow surrounding the thermal column. The downward-moving exterior
12320-421: The asymmetrical structure of Sally, almost all of Florida saw continuous shower and thunderstorm activity starting on September 12. A low-topped supercell in the outer rainbands of Sally prompted a tornado warning east of Tampa near Sebring on September 12. The next day, another storm prompted two tornado warnings in southwestern Lee County . Several special marine warnings were also issued for
12474-468: The backside of the storm became established over the Florida Peninsula within an environment highly favoring extreme rainfall rates. A temporary reprieve in wind shear enabled Sally's core to become more vertically aligned and convective bursts occurred throughout the day into September 14. Following a burst of deep convection with tops colder than −112 °F (−80 °C), Sally underwent
12628-531: The border into the Florida Panhandle , the hurricane weakened to a tropical storm by 18:00 UTC as it moved back over southeastern Alabama. During this time, its forward motion steadily increased as it interacted with the mid-latitude westerlies . Convection surrounding the center eroded amid increasing wind shear and the influence of land-based friction. Excellent outflow aloft supported continued heavy rain across central Georgia in areas northeast of
12782-753: The center and Sally slowly intensified. On September 14, a center reformation into the center of the convection occurred, and data from a hurricane hunter reconnaissance aircraft showed that Sally had rapidly intensified into a strong Category 1 hurricane. However, an increase in wind shear and upwelling of colder waters halted the intensification and Sally weakened slightly on September 15 before turning slowly northeastward. Despite this increase in wind shear, it unexpectedly re-intensified, reaching Category 2 status early on September 16 before making landfall at peak intensity at 09:45 UTC on September 16, near Gulf Shores, Alabama , with maximum sustained winds of 110 mph (180 km/h) and
12936-422: The center. Moist southerly flow from Sally interacted with a developing frontal boundary over the state and expanded the breadth of heavy rain. Sally degraded to a tropical depression by 06:00 UTC on September 17 as its surface circulation decoupled from its mid- to upper-level circulation, with the latter accelerating ahead. The system transitioned into post-tropical cyclone soon after as it merged with
13090-485: The city and a power outage on the eastern side of the city. Some parts of South Mississippi also reported uprooted trees and downed signs. Overall damage in Mississippi was expected to be much greater, but was reduced because the storm shifted east. In Georgia , six tornadoes were confirmed, of which two were rated EF1 while the other four were rated EF0. One person was killed and two others were injured after
13244-406: The coast and called for evacuations of low-lying and flood prone areas. Additionally, Dauphin Island mayor Jeff Collier strongly encouraged all people to evacuate the west end after water started to encroach on the main roadway. A state of emergency was declared by governor Kay Ivey on September 14, 2020, as public schools and university classes were either canceled or moved online in anticipation of
13398-459: The coast of Apalachee Bay . Rainfall continued to spread west into Alabama and slightly inland and its persistence led to soil saturation of 85 percent well-before the storm's core arrived. Operationally, the NHC upgraded the storm to low-end Category 2 status at 21:00 UTC, but this was determined to be due to transient eyewall features and not a true estimate of the storm's intensity. By
13552-667: The constant wave action with one of them hitting a dock. Fort Morgan, Alabama reported a wind gust of 121 miles per hour (195 km/h) while Mobile reported a wind gust of 83 miles per hour (134 km/h). Major structural damage was recorded at the landfall point in Gulf Shores as well as Mobile. A pier in Gulf Shores that was destroyed in Hurricane Ivan in 2004 was partially destroyed again by storm surge from Sally just days after it had reopened following renovations. There were also several reports of damage to condos in
13706-640: The core and in rainbands east of the center became more intense during this period. "Significant and life threatening flash flooding" began late on September 15 as rainfall intensified to rates up 3 in (76 mm) per hour along the coast, primarily between Gulf Shores, Alabama , and Destin, Florida . The Weather Prediction Center soon described it as "catastrophic flash flooding" as accumulations exceeded 18 in (460 mm) within 24 hours with rainfall rates up to 4 in (100 mm) per hour still occurring. Additional rainbands developed farther east near Panama City and Apalachicola , expanding
13860-530: The day as it approached the northwest side of a weak ridge. Although wind shear did not abate, upper-level divergence increased significantly and enabled the hurricane to unexpectedly intensify as it approached the Alabama coastline. Its eye became increasingly well-defined and aircraft observations revealed a major increase in both flight-level and surface winds; elevated winds up to 131 mph (211 km/h) were detected by Doppler weather radar. Convection around
14014-435: The development of the westerlies . Cyclone formation is usually reduced 3 days prior to the wave's crest and increased during the 3 days after. The majority of tropical cyclones each year form in one of seven tropical cyclone basins, which are monitored by a variety of meteorological services and warning centers. Ten of these warning centers worldwide are designated as either a Regional Specialized Meteorological Centre or
14168-470: The earth and the base of a cumulonimbus cloud (thundercloud), or a cumulus cloud in rare cases. Tornadoes come in many sizes but typically form a visible condensation funnel whose narrowest end reaches the earth and is surrounded by a cloud of debris and dust . Tornadoes wind speeds generally average between 64 kilometres per hour (40 mph) and 180 kilometres per hour (110 mph). They are approximately 75 metres (246 ft) across and travel
14322-592: The entirety of Gulf Islands National Seashore on September 12. The mayor of New Orleans , LaToya Cantrell , issued an evacuation for areas outside the levee system of the city, due to expected storm surge. The governor of Louisiana declared a state of emergency for the entire state, which was still recovering from the devastating effects of Hurricane Laura just three weeks earlier. Several parishes and areas were put under mandatory evacuation orders including all of St. Charles Parish , and parts of Orleans Parish , Jefferson Parish , Plaquemines Parish , and St. John
14476-492: The equator, then move poleward past the ridge axis before recurving into the main belt of the Westerlies . When the subtropical ridge position shifts due to El Niño, so will the preferred tropical cyclone tracks. Areas west of Japan and Korea tend to experience much fewer September–November tropical cyclone impacts during El Niño and neutral years. During La Niña years, the formation of tropical cyclones, along with
14630-469: 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. The strong rotating winds of
14784-409: The extreme case, a derecho can cover a huge area more than 320 kilometres (200 mi) wide and over 1,600 kilometres (990 mi) long, lasting up to 12 hours or more, and is associated with some of the most intense straight-line winds, but the generative process is somewhat different from that of most downbursts. A tornado is a dangerous rotating column of air in contact with both the surface of
14938-481: The eyewall of the storm, and an upper-level anticyclone helps channel this air away from the cyclone efficiently. However, some cyclones such as Hurricane Epsilon have rapidly intensified despite relatively unfavorable conditions. 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
15092-554: The fact that there might be a layer in the atmosphere that has positive values of CAPE, if the parcel does not reach or begin rising to that level, the most significant convection that occurs in the FCL will not be realized. This can occur for numerous reasons. Primarily, it is the result of a cap, or convective inhibition (CIN/CINH) . Processes that can erode this inhibition are heating of the Earth's surface and forcing. Such forcing mechanisms encourage upward vertical velocity, characterized by
15246-486: The final one became lodged underneath the Pensacola Bay Bridge , located between cities of Pensacola and the Gulf Breeze causing the bridge to be temporarily closed. The next morning, a crane fell onto the same bridge, destroying a portion of the roadway. The Florida Department of Transportation was unable to assess any possible damage to the bridge due to ongoing high Water main breaks occurred inside
15400-435: The first 24 hours and over 30 inches in 48 hours. Numerous tornadoes also occurred as well. Damage is estimated at $ 7.3 billion (2020 USD). Sally was the costliest of several destructive 2020 hurricanes whose names were not retired by the World Meteorological Organization following the season, along with Hanna , Isaias , Delta , and Zeta . Toward the end of August 2020, a shortwave trough interacted with
15554-399: The first 24 hours and over 30 inches in 48 hours. Several area tornadoes also occurred. Damage totals are estimated to be $ 7 million to Gulf Breeze public facilities. The unincorporated Tiger Point saw 36 inches (91 cm) of rain, while Bellview saw 30 inches (76 cm). In Pensacola itself, over 24 inches (61 cm) of rain fell and storm surge flooding reached 5.6 feet (1.7 m),
15708-410: 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. Conversely, the mixing of
15862-453: The frequency of very intense storms and a poleward extension of where the cyclones reach maximum intensity are among the possible consequences of human-induced climate change. Tropical cyclones use warm, moist air as their fuel. As climate change is warming ocean temperatures , there is potentially more of this fuel available. Between 1979 and 2017, there was a global increase in the proportion of tropical cyclones of Category 3 and higher on
16016-532: The general public regarding forecasts, watches, and warnings. Since the systems can last a week or longer, and more than one can be occurring in the same basin at the same time, the names are thought to reduce the confusion about what storm is being described. Names are assigned in order from predetermined lists with one, three, or ten-minute sustained wind speeds of more than 65 km/h (40 mph) depending on which basin it originates. Standards vary from basin to basin. Some tropical depressions are named in
16170-472: The hail-producing thunderstorm, whose top is usually greater than 10 kilometres (6.2 mi) high. It then falls toward the ground while continuing to grow, based on the same processes, until it leaves the cloud. It will later begin to melt as it passes into the air above freezing temperature Thus, a unique trajectory in the thunderstorm is sufficient to explain the layer-like structure of the hailstone. The only case in which we can discuss multiple trajectories
16324-597: The hours that followed. Several tornado , flash flood , and flood watches were issued. States of emergency were declared in the states of Louisiana , Mississippi , and Alabama in preparation for Sally's arrival. Emergencies were also declared in the East Baton Rouge and St. Bernard parishes in Louisiana and Escambia , Santa Rosa and Okaloosa counties in Florida as well as New Orleans and Pensacola, Florida . The National Park Service shut down
16478-542: The imbalance of Coriolis and pressure gradient forces, causing subgeostrophic and supergeostrophic flows , can also create upward vertical velocities. There are numerous other atmospheric setups in which upward vertical velocities can be created. Buoyancy is a key to thunderstorm growth and is necessary for any of the severe threats within a thunderstorm. There are other processes, not necessarily thermodynamic, that can increase updraft strength. These include updraft rotation , low-level convergence, and evacuation of mass out of
16632-555: The imminent approach of Sally, and several coastline counties and parishes on the Gulf Coast were evacuated. In South Florida , heavy rain led to localized flash flooding while the rest of peninsula saw continuous shower and thunderstorm activity due to the asymmetric structure of Sally. The area between Mobile, Alabama , and Pensacola - Gulf Breeze, Florida took the brunt of the storm with widespread wind damage, storm surge flooding, and over 20 inches (510 mm) of rainfall in
16786-458: The instability and relative wind conditions at different layers of the atmosphere (" wind shear "). Single-cell thunderstorms form in environments of low vertical wind shear and last only 20–30 minutes. Organized thunderstorms and thunderstorm clusters/lines can have longer life cycles as they form in environments of significant vertical wind shear, which aids the development of stronger updrafts as well as various forms of severe weather. The supercell
16940-451: The intensity from leveling off before an eye emerges in infrared imagery. The SATCON weights estimates from various satellite-based systems and microwave sounders , accounting for the strengths and flaws in each individual estimate, to produce a consensus estimate of a tropical cyclone's intensity which can be more reliable than the Dvorak technique at times. Multiple intensity metrics are used, including accumulated cyclone energy (ACE),
17094-522: The intensity of a tropical cyclone. Reconnaissance aircraft fly around and through tropical cyclones, outfitted with specialized instruments, to collect information that can be used to ascertain the winds and pressure of a system. Tropical cyclones possess winds of different speeds at different heights. Winds recorded at flight level can be converted to find the wind speeds at the surface. Surface observations, such as ship reports, land stations, mesonets , coastal stations, and buoys, can provide information on
17248-643: The large amount of damage in the city, a curfew was imposed in Mobile, Alabama , starting on September 16. Immediately after the storm, the Cajun Navy , a nonprofit rescue organization, began surveying damage in Alabama. The agricultural industry of Alabama , which was already under stress due to COVID -related impacts, suffered another devastating blow with many farmers' fields completely flooded, crops torn apart, and structures destroyed. Strong winds and heavy rainfall devastated crops, leaving many farmers across
17402-693: The late 1800s and early 1900s and gradually superseded the existing system—simply naming cyclones based on what they hit. The system currently used provides positive identification of severe weather systems in a brief form, that is readily understood and recognized by the public. The credit for the first usage of personal names for weather systems is generally given to the Queensland Government Meteorologist Clement Wragge who named systems between 1887 and 1907. This system of naming weather systems fell into disuse for several years after Wragge retired, until it
17556-404: 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. Should a tropical cyclone make landfall or pass over an island, its circulation could start to break down, especially if it encounters mountainous terrain. When a system makes landfall on a large landmass, it
17710-455: The moisture condenses, it releases energy known as latent heat of vaporization which allows the rising packet of air to cool less than its surrounding air, continuing the cloud's ascension. If enough instability is present in the atmosphere, this process will continue long enough for cumulonimbus clouds to form, which supports lightning and thunder. Generally, thunderstorms require three conditions to form: moisture, an unstable airmass, and
17864-662: The nineteenth of the season, by 18:00 UTC that day while situated between Andros Island and Bimini in the Bahamas, or about 115 mi (185 km/h) east-southeast of Miami , Florida. A subtropical ridge over the Southeastern United States steered the system generally west-northwest toward the Florida Peninsula . Around 06:00 UTC on September 12, the depression made landfall near Cutler Bay , Florida, with maximum sustained winds of 35 mph (55 km/h). Within hours, multiple weather stations began recording sustained tropical storm-force winds and
18018-763: The northern eyewall for hours. Over 500,000 customers in Louisiana , Alabama , Florida , and Georgia lost power and parts of I-10 , including the Escambia Bay Bridge , were shut down. Widespread tornado , special marine , severe thunderstorm , and flash flood warnings were issued, including several flash flood emergencies . Sally was the most destructive storm to strike the Alabama–Florida border region in nearly 20 years, which included Baldwin County in Alabama and Escambia County in Florida. Due to
18172-522: The observed trend of rapid intensification of tropical cyclones in the Atlantic basin. Rapidly intensifying cyclones are hard to forecast and therefore pose additional risk to coastal communities. Warmer air can hold more water vapor: the theoretical maximum water vapor content is given by the Clausius–Clapeyron relation , which yields ≈7% increase in water vapor in the atmosphere per 1 °C (1.8 °F) warming. All models that were assessed in
18326-455: The others were rated EF0. One person was injured indirectly as he was cleaning up debris from his mobile home following an EF0 tornado in Sardis, South Carolina . The storm caused widespread power outages across Baldwin County . Restoration of power took several days to bring back to 100%. The cities of Gulf Shores and Foley suffered the most extensive damage in Baldwin County. Due
18480-466: The overall frequency of tropical cyclones worldwide, with increased frequency in the North Atlantic and central Pacific, and significant decreases in the southern Indian Ocean and western North Pacific. There has been a poleward expansion of the latitude at which the maximum intensity of tropical cyclones occurs, which may be associated with climate change. In the North Pacific, there may also have been an eastward expansion. Between 1949 and 2016, there
18634-452: The parcel with environmental air. Atmospheric convection is called "deep" when it extends from near the surface to above the 500 hPa level, generally stopping at the tropopause at around 200 hPa . Most atmospheric deep convection occurs in the tropics as the rising branch of the Hadley circulation and represents a strong local coupling between the surface and the upper troposphere which
18788-422: The parcel's vertical momentum may carry it to the maximum parcel level (MPL) where the negative buoyancy decelerates the parcel to a stop. Integrating the buoyancy force over the parcel's vertical displacement yields convective available potential energy (CAPE) , the joules of energy available per kilogram of potentially buoyant air. CAPE is an upper limit for an ideal undiluted parcel, and the square root of twice
18942-440: The potential of spawning tornadoes . Climate change affects tropical cyclones in several ways. Scientists found that climate change can exacerbate the impact of tropical cyclones by increasing their duration, occurrence, and intensity due to the warming of ocean waters and intensification of the water cycle . Tropical cyclones draw in air from a large area and concentrate the water content of that air into precipitation over
19096-465: The potential for tropical cyclogenesis on September 9, anticipating the system to not become a tropical cyclone until reaching the Gulf of Mexico several days later. A broad surface slow steadily coalesced with accompanying convection becoming more organized as the system approached the archipelago on September 11. Contrary to the NHC's forecasts, the system developed into a tropical depression,
19250-413: The presence of moderate or strong wind shear depending on the evolution and structure of the storm's convection. 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. The Fujiwhara effect , which involves interaction between two tropical cyclones, can weaken and ultimately result in the dissipation of
19404-444: The release of latent heat from the saturated soil. Orographic lift can cause a 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. Jet streams can both enhance and inhibit tropical cyclone intensity by influencing the storm's outflow as well as vertical wind shear. On occasion, tropical cyclones may undergo
19558-588: The remnant system interacted with an unseasonably strong cold front, creating an axis of heavy rain across the region. The rain event associated with Sally finally ceased late on September 18 as the new system moved farther offshore. Due to the possibility of the storm making landfall as a tropical storm, a tropical storm watch was issued for the coast of Southeastern Florida from south of Jupiter Inlet to north of Ocean Reef when advisories were first issued at 21:00 UTC on September 11. At 03:00 UTC on September 12, another tropical storm watch
19712-492: The same intensity. The passage of a tropical cyclone over the ocean causes the upper layers of the ocean to cool substantially, a process known as upwelling , 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
19866-492: The same system. The ASCAT is a scatterometer used by the MetOp satellites to map the wind field vectors of tropical cyclones. The SMAP uses an L-band radiometer channel to determine the wind speeds of tropical cyclones at the ocean surface, and has been shown to be reliable at higher intensities and under heavy rainfall conditions, unlike scatterometer-based and other radiometer-based instruments. The Dvorak technique plays
20020-633: The scope of the flood event. Sally's northern eyewall began moving onshore in Baldwin County, Alabama , between Mobile Bay and Pensacola Bay around 05:00 UTC. Mesovortices within the eyewall battered the coastline with violent wind gusts during this time. The storm reached Category 2 intensity by 06:00 UTC as it approached Mobile Bay and continued to intensify until its center reached land. The hurricane ultimately made landfall at peak strength in Gulf Shores at 09:45 UTC with maximum sustained winds of 110 mph (175 km/h) and
20174-513: The sea can result in heat being inserted in deeper waters, with potential effects on global climate . Vertical wind shear decreases tropical cyclone predicability, with storms exhibiting wide range of responses in the presence of shear. Wind shear often negatively affects tropical cyclone intensification by displacing moisture and heat from a system's center. Low levels of vertical wind shear are most optimal for strengthening, while stronger wind shear induces weakening. Dry air entraining into
20328-505: The south side of Lake Pontchartrain in Louisiana to overflow its banks, flooding Lakeshore Drive. However, no serious damage was reported as the storm veered farther east than originally forecast. Sally brought flooding to Mississippi, with the worst in Jackson County . At the peak of the storm, more than 10,000 people were without power along the Gulf Coast. Pascagoula police reported downed power lines and traffic lights in
20482-436: The start of September 15, steering currents collapsed and Sally largely stalled south of the Florida Panhandle and Mobile Bay with a slight drift west. A sudden increase in wind shear caused the hurricane's structure to degrade, with its core becoming asymmetric. An intrusion of dry air caused the eye to open up to the south. The hurricane's forward motion gradually shifted to the north and later north-northeast throughout
20636-573: The state without hopes for a successful harvest. Tropical cyclone A tropical cyclone is a rapidly rotating storm system with 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 called a hurricane ( / ˈ h ʌr ɪ k ən , - k eɪ n / ), typhoon ( / t aɪ ˈ f uː n / ), tropical storm , cyclonic storm , tropical depression , or simply cyclone . A hurricane
20790-419: The storm cleanup process. Over 2,000 broken poles and 4,300 trees on power lines left over 71,000 households and businesses in southern and central Baldwin County without power, representing 95% of the service area of a local electrical cooperative , Baldwin EMC. Only 5 of 22 substations remained in service the day after the storm. Two days after landfall, on September 18, Alabama governor Kay Ivey said in
20944-579: The storm. On September 14 at 6:00pm, the Pensacola International Airport closed. Warm and humid southerly flow associated with the circulation of Sally brought scattered showers and thunderstorms to western and central areas of Cuba on September 12–13. The re-intensification and sudden track to the east by Sally prior to landfall caught many by surprise. Additionally, the storm's slow movement caused coastal areas between Mobile, Alabama , and Pensacola, Florida , to be in
21098-617: The subtropical ridge position, shifts westward across the western Pacific Ocean, which increases the landfall threat to China and much greater intensity in the Philippines . The Atlantic Ocean experiences depressed activity due to increased vertical wind shear across the region during El Niño years. Tropical cyclones are further influenced by the Atlantic Meridional Mode , the Quasi-biennial oscillation and
21252-419: 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. 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
21406-483: 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
21560-648: The system and its intensity. For example, within the Northern Atlantic and Eastern Pacific basins, a tropical cyclone with wind speeds of over 65 kn (120 km/h; 75 mph) is called a hurricane , while it is called a typhoon or a severe cyclonic storm within the Western Pacific or North Indian oceans. When a hurricane passes west across the International Dateline in the Northern Hemisphere, it becomes known as
21714-538: The system became Tropical Storm Sally by 12:00 UTC while situated over the Everglades . This marked the earliest formation of a season's 18th named storm, surpassing the previous record of October 2 set in 2005 with Hurricane Stan . As Sally emerged over the eastern Gulf of Mexico later on September 12, banding features became increasingly defined over the southern portion of its circulation. One of these bands became somewhat stationary, pivoting over
21868-415: The temporal resolution of forecast model soundings is greater than the direct measurements, where the former can have plots for intervals of up to every 3 hours, and the latter as having only 2 per day (although when a convective event is expected a special sounding might be taken outside of the normal schedule of 00Z and then 12Z.). Atmospheric convection can also be responsible for and have implications on
22022-542: The third highest surge ever recorded in the city. Many streets were flooded and several parked cars were totaled when water got into their engines. Late on September 15, twenty-two barges in the Pensacola Bay broke loose due to heavy surf. Five of the barges washed up near downtown while the sixth was involved in another collision. The seventh lodged itself underneath the Garcon Point Bridge while
22176-403: The top of the updraft via strong upper-level winds and the jet stream . Like other precipitation in cumulonimbus clouds hail begins as water droplets. As the droplets rise and the temperature goes below freezing, they become supercooled water and will freeze on contact with condensation nuclei . A cross-section through a large hailstone shows an onion-like structure. This means the hailstone
22330-423: The tropical cyclone year begins on July 1 and runs all year-round encompassing the tropical cyclone seasons, which run from November 1 until the end of April, with peaks in mid-February to early March. Of various modes of variability in the climate system, El Niño–Southern Oscillation has the largest effect on tropical cyclone activity. Most tropical cyclones form on the side of the subtropical ridge closer to
22484-478: The upper parts of the atmosphere, or a surplus of mass in the low levels of the atmosphere, which would lead to upper-level divergence or lower-level convergence, respectively. An Upward vertical motion will often follow. Specifically, a cold front , sea/lake breeze , outflow boundary , or forcing through vorticity dynamics ( differential positive vorticity advection ) of the atmosphere such as with troughs, both shortwave and longwave . Jet streak dynamics through
22638-430: The varying thicknesses of the layers of the hailstone. The accretion rate of supercooled water droplets onto the hailstone depends on the relative velocities between these water droplets and the hailstone itself. This means that generally, the larger hailstones will form some distance from the stronger updraft where they can pass more time growing As the hailstone grows it releases latent heat , which keeps its exterior in
22792-451: The weaker of two tropical cyclones by reducing the organization of the system's convection and imparting horizontal wind shear. Tropical cyclones typically weaken while situated over a landmass because conditions are often unfavorable as a result of the lack of oceanic forcing. 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
22946-402: The wind speed of Hurricane Helene by 11%, it increased the destruction from it by more than twice. According to World Weather Attribution the influence of climate change on the rainfall of some latest hurricanes can be described as follows: Tropical cyclone intensity is based on wind speeds and pressure. Relationships between winds and pressure are often used in determining the intensity of
23100-795: 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 . Warm sea surface temperatures are required 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). Higher sea surface temperatures result in faster intensification rates and sometimes even rapid intensification . High ocean heat content , also known as Tropical Cyclone Heat Potential , allows storms to achieve
23254-475: Was a slowdown in tropical cyclone translation speeds. It is unclear still to what extent this can be attributed to climate change: climate models do not all show this feature. A 2021 study review article concluded that the geographic range of tropical cyclones will probably expand poleward in response to climate warming of the Hadley circulation . When hurricane winds speed rise by 5%, its destructive power rise by about 50%. Therfore, as climate change increased
23408-568: Was declared on the night of Sunday, September 13, 2020. Mississippi governor Tate Reeves urged residents to prepare for Sally, which he said could produce up to 20 inches (510 mm) of rain in the southern part of the state. Some shelters were opened, although officials urged people who were evacuating to stay with friends, relatives, or in hotels, if possible, because of the threat of coronavirus superspreading. Mandatory evacuations were ordered for parts of Harrison County and Hancock County . Alabama governor Kay Ivey closed all beaches on
23562-580: Was issued for the Florida panhandle from the Ochlockonee River to the Okaloosa / Walton County line. That same day, numerous storm surge, tropical storm, and hurricane watches were then issued for a large portion of the US Gulf Coast east of New Orleans at 21:00 UTC, three hours after Sally was named. Many of these watches were then upgraded to warnings at 09:00 UTC on September 13 with more watches and warnings issued in
23716-585: Was revived in the latter part of World War II for the Western Pacific. Formal naming schemes have subsequently been introduced for the North and South Atlantic, Eastern, Central, Western and Southern Pacific basins as well as the Australian region and Indian Ocean. At present, tropical cyclones are officially named by one of twelve meteorological services and retain their names throughout their lifetimes to provide ease of communication between forecasters and
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