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In meteorology, a cyclone is a large air mass that rotates around a strong center of low atmospheric pressure, counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere as viewed from above. Cyclones are characterized by inward-spiraling winds that rotate about a zone of low pressure. The largest low-pressure systems are polar vortices and extratropical cyclones of the largest scale. Warm-core cyclones such as tropical cyclones and subtropical cyclones also lie within the synoptic scale. Mesocyclones, tornadoes, and dust devils lie within the smaller mesoscale. Upper level cyclones can exist without the presence of a surface low, and can pinch off from the base of the tropical upper tropospheric trough during the summer months in the Northern Hemisphere. Cyclones have also been seen on extraterrestrial planets, such as Mars, Jupiter, and Neptune. Cyclogenesis is the process of cyclone formation and intensification. Extratropical cyclones begin as waves in large regions of enhanced mid-latitude temperature contrasts called baroclinic zones. These zones contract and form weather fronts as the cyclonic circulation closes and intensifies. Later in their life cycle, extratropical cyclones occlude as cold air masses undercut the warmer air and become cold core systems. A cyclone's track is guided over the course of its 2 to 6 day life cycle by the steering flow of the subtropical jet stream.
A subtropical cyclone is a weather system that has some characteristics of both tropical and an extratropical cyclone.
South Atlantic tropical cyclones are unusual weather events that occur in the Southern Hemisphere. Strong wind shear, which disrupts the formation of cyclones, as well as a lack of weather disturbances favorable for development in the South Atlantic Ocean, make any strong tropical system extremely rare, and Hurricane Catarina in 2004 is the only recorded South Atlantic hurricane in history. Storms can develop year-round in the South Atlantic, with activity peaking during the months from November through May. Since 2011, the Brazilian Navy Hydrographic Center has assigned names to tropical and subtropical systems in the western side of the basin, near the eastern coast of Brazil, when they have sustained wind speeds of at least 65 km/h (40 mph), the generally accepted minimum sustained wind speed for a disturbance to be designated as a tropical storm in the North Atlantic basin. Below is a list of notable South Atlantic tropical and subtropical cyclones.
The 2003 Atlantic hurricane season was a highly active Atlantic hurricane season with tropical activity before and after the official bounds of the season—the first such occurrence since the 1970 season. The season produced 21 tropical cyclones, of which 16 developed into named storms; seven of those attained hurricane status, of which three reached major hurricane status. With sixteen storms, the season was tied for the fifth-most active Atlantic hurricane season on record, although it has since dropped down to become the seventh most active season. The strongest hurricane of the season was Hurricane Isabel, which reached Category 5 status on the Saffir–Simpson hurricane scale northeast of the Lesser Antilles; Isabel later struck North Carolina as a Category 2 hurricane, causing $3.6 billion in damage and a total of 51 deaths across the Mid-Atlantic region of the United States.
The 2002 Atlantic hurricane season was a near-average Atlantic hurricane season. It officially started on June 1, 2002, and ended on November 30, dates which conventionally limit the period of each year when most tropical cyclones develop in the Atlantic Ocean. The season produced fourteen tropical cyclones, of which twelve developed into named storms; four became hurricanes, and two attained major hurricane status. While the season's first cyclone did not develop until July 14, activity quickly picked up: eight storms developed in the month of September. It ended early however, with no tropical storms forming after October 6—a rare occurrence caused partly by El Niño conditions. The most intense hurricane of the season was Hurricane Isidore with a minimum central pressure of 934 mbar, although Hurricane Lili attained higher winds and peaked at Category 4 whereas Isidore only reached Category 3. However, Lili had a minimum central pressure of 938 mbar.
The 1962 Atlantic hurricane season featured Hurricanes Daisy and Ella – two tropical cyclones that showed the latest dates for the fourth and fifth named storms on record since tropical cyclones were first named in the North Atlantic ocean, starting in 1950, when they both formed on September 29 and October 14. On the same hand, it was the least active since 1939, with only five named storms. Although the season officially began on June 15, the first named storm did not form until August 26, the third-latest date. Hurricane Alma brushed the Outer Banks before becoming extratropical southeast of New England, destroying hundreds of boats and producing beneficial rainfall. In late August, Tropical Storm Becky developed unusually far east in the Atlantic Ocean, becoming the easternmost storm on record to recurve to the northeast. Celia followed in the September, forming east of the Lesser Antilles and executing a loop near Bermuda before dissipating. Hurricane Daisy, the latest fourth named storm, was the costliest of the season, leaving about $1.1 million in damage in New England (1962 USD). The storm dropped the highest rainfall total on record in Maine, and its precipitation caused 22 traffic fatalities. The final hurricane – Ella – the latest fifth named storm – was also the strongest, remaining offshore of the eastern United States but causing two deaths.
The 1923 Atlantic hurricane season featured 11 tropical cyclones, 9 of which intensified into tropical storms, the most since 1916. Four of the tropical storms intensified into hurricanes, one of which reached major hurricane intensity—Category 3 or higher on the modern-day Saffir–Simpson hurricane wind scale. No tropical storms or hurricanes formed in or entered the Caribbean Sea. The first known system, a tropical depression, formed on June 19, while the last known system, a tropical storm, transitioned into an extratropical cyclone on October 26. A total of Additionally, an October tropical depression was previously recognized as a tropical storm until reanalysis in 2009, while the first and third tropical storms were added to the Atlantic hurricane database that year. The sixth, seven, and eight storms as well as the October tropical depression existed simultaneously on October 16.
The 1913 Atlantic hurricane season was the third consecutive year with a tropical cyclone developing before June. The first system, a tropical depression, developed on May 5 while the last transitioned into an extratropical cyclone on October 30. Of note, the seventh and eighth cyclones existed simultaneously from August 30 to September 4.
The 1905 Atlantic hurricane season featured five known tropical cyclones, two of which made landfall in the United States. The first system was initially observed near the Windward Islands on September 6. The last system to dissipate, the fourth storm, transitioned into an extratropical cyclone on October 11, while located well southeast of Newfoundland. These dates fall within the period with the most tropical cyclone activity in the Atlantic. Between October 5 and October 10, the fourth and fifth system existed simultaneously.
Hurricane Kate was a long-lived and erratic tropical cyclone that caused minor impacts across the Atlantic Ocean from late September to early October 2003. The sixteenth tropical cyclone, eleventh tropical storm, seventh hurricane, and third major hurricane of the 2003 Atlantic hurricane season, Kate developed from a tropical wave in the central tropical Atlantic on September 25. Its unusual track included four major changes in direction. The storm moved northwestward until a weakness in the subtropical ridge forced it eastward. Kate strengthened to a hurricane, turned sharply westward while moving around a mid-level low, and intensified to a 125 mph (201 km/h) major hurricane on October 4. Kate turned sharply northward around the periphery of an anticyclone, weakened, and became extratropical after passing to the east of Newfoundland. The extratropical storm persisted for three days until losing its identity near Scandinavia.
Extratropical cyclones, sometimes called mid-latitude cyclones or wave cyclones, are low-pressure areas which, along with the anticyclones of high-pressure areas, drive the weather over much of the Earth. Extratropical cyclones are capable of producing anything from cloudiness and mild showers to severe gales, thunderstorms, blizzards, and tornadoes. These types of cyclones are defined as large scale (synoptic) low pressure weather systems that occur in the middle latitudes of the Earth. In contrast with tropical cyclones, extratropical cyclones produce rapid changes in temperature and dew point along broad lines, called weather fronts, about the center of the cyclone.
The 1987 Atlantic hurricane season was a below-average hurricane season that was limited by an ongoing El Niño. The season officially began on June 1, 1987, and lasted until November 30, 1987, although activity began on May 24 when a tropical depression developed 400 mi (640 km) east of the central Bahamas. The June through November dates conventionally delimit the period of each year when most tropical cyclones form in the Atlantic basin. The first cyclone to attain tropical storm status was an unnamed tropical storm which formed on August 9, nearly a month later than usual. The final storm of the year, Tropical Depression Fourteen, merged with a weak extratropical low on November 4. The season marked the first year tropical storm watches and warnings were issued; previously, gale watches and warnings were used for tropical storms, and this season was one of only a few seasons with no deaths in the United States; the last time this happened was in the 1981 season.
Tropical Storm Chantal was a short-lived tropical storm that affected Bermuda in its formative stages and caused flooding and gusty winds in Newfoundland while extratropical. The third named storm of the 2007 Atlantic hurricane season, Chantal developed on July 31 from non-tropical origins between Bermuda and Cape Cod, and with favorable conditions, the storm rapidly attained peak winds of 50 mph (80 km/h). The storm accelerated northeastward over an area of progressively colder water temperatures, and after a decrease in convection the National Hurricane Center ceased issuing advisories as Chantal began undergoing extratropical transition early on August 1. Shortly thereafter, the extratropical remnant crossed over southeastern Newfoundland before tracking into the open waters of the north Atlantic Ocean. Prior to forming, the storm dropped moderate rainfall on Bermuda. Subsequent to becoming extratropical, the remnants of Chantal produced gusty winds and heavy precipitation across the Avalon Peninsula of Newfoundland, causing flooding and wind damage; insured damage totaled $25 million.
The 2006 Central Pacific cyclone, also known as Invest 91C or Storm 91C, was an unusual weather system that formed in 2006. Forming on October 30 from a mid-latitude cyclone in the north Pacific mid-latitudes, it moved over waters warmer than normal. The system acquired some features more typical of subtropical and even tropical cyclones. However, as it neared the western coastline of North America, the system fell apart, dissipating soon after landfall, on November 4. Moisture from the storm's remnants caused substantial rainfall in British Columbia and the Pacific Northwest. The exact status and nature of this weather event is unknown, with meteorologists and weather agencies having differing opinions.
The October 2009 North American storm complex was a powerful extratropical cyclone that was associated with the remnants of Typhoon Melor, which brought extreme amounts of rainfall to California. The system started out as a weak area of low pressure, that formed in the northern Gulf of Alaska on October 7. Late on October 11, the system quickly absorbed Melor's remnant moisture, which resulted in the system strengthening significantly offshore, before moving southeastward to impact the West Coast of the United States, beginning very early on October 13. Around the same time, an atmospheric river opened up, channeling large amounts of moisture into the storm, resulting in heavy rainfall across California and other parts of the Western United States. The storm caused at least $8.861 million in damages across the West Coast of the United States.
The March 2014 nor'easter was an extremely powerful extratropical cyclone that affected much of U.S. Gulf Coast, the eastern United States, eastern Canada, and Greenland. It was the most powerful winter storm of the 2013–14 North American winter storm season, being an unusually large winter storm as well, with its gale-force wind field becoming four times larger than that of Hurricane Sandy's extratropical remnant. The storm affected various parts of the Midwest, most of the Eastern Seaboard, as well as eastern Canada, bringing extremely powerful winds, and blizzard-like conditions.
The 2021 Atlantic hurricane season was the third-most active Atlantic hurricane season on record, although many storms were weak and short-lived. With 21 named storms forming, it became the second season in a row and third overall in which the designated 21-name list of storm names was exhausted. Seven of those storms strengthened into a hurricane, four of which reached major hurricane intensity, which is slightly above-average. The season officially began on June 1 and ended on November 30. These dates historically describe the period in each year when most Atlantic tropical cyclones form. However, subtropical or tropical cyclogenesis is possible at any time of the year, as demonstrated by the development of Tropical Storm Ana on May 22, making this the seventh consecutive year in which a storm developed outside of the official season.
Hurricane Chris was a moderately strong tropical cyclone that affected the East Coast of the United States and Atlantic Canada in July 2018. The third tropical or subtropical cyclone, third named storm, and second hurricane of the 2018 Atlantic hurricane season, Chris originated from a frontal system that moved offshore the coast of the northeastern United States on June 29. The front evolved into a non-tropical low by July 3. After further organization, a tropical depression formed on July 6, several hundred miles south-southeast of Cape Hatteras, North Carolina. Two days later, the depression strengthened into a tropical storm and received the name Chris. Chris slowly strengthened as it drifted into warmer waters. These favorable conditions allowed Chris to rapidly intensify into a hurricane on July 10. The hurricane reached its peak intensity with winds of 105 mph (165 km/h) and a pressure of 969 mbar (28.61 inHg) at. This peak intensity was short-lived though, as Chris began to undergo extratropical transition. At 12:00 UTC on July 12, Chris became an extratropical cyclone well southeast of Newfoundland. The low continued northeastward over the Atlantic for the next few days, before weakening and finally dissipating southeast of Iceland on July 17.
Severe Tropical Cyclone Niran was a very powerful tropical cyclone that brought severe impacts to extreme Northeastern Australia and nearly made landfall in New Caledonia in February and March 2021. The sixth tropical cyclone and the second severe tropical cyclone of the 2020–21 Australian region cyclone season, while being the third severe tropical cyclone of the annual South Pacific cyclone season, Niran was the second Category 5 severe tropical cyclone in the South Pacific cyclone season, following Cyclone Yasa. The cyclone formed from a tropical low in the Coral Sea on 27 February. The tropical low gradually intensified while stalling offshore of Queensland for several days, although disorganized at the time. Early on 3 March, Niran pulled away from the coast of Australia, while it started undergoing rapid intensification. Eventually, Niran reached its peak intensity as a Category 5 tropical cyclone on both the Australian Tropical Cyclone Scale and the Saffir–Simpson scale, on 5 March, well offshore of Australia. Soon afterward, Niran initiated an eyewall replacement cycle and encountered some wind shear, causing the storm to weaken on 6 March, as it passed just to the south of Grande Terre, the main island of New Caledonia. Afterwards, Niran continued rapidly weakening as wind shear increased further, before transitioning into an extratropical cyclone late on 6 March. Niran was absorbed into another extratropical storm two days later.
Hurricane Larry was a strong and long-lived Cape Verde hurricane that became the first hurricane to make landfall in Newfoundland since Igor in 2010. The twelfth named storm, fifth hurricane, and third major hurricane of the 2021 Atlantic hurricane season, Larry originated from a tropical wave that emerged off the coast of Africa and organized into a tropical depression on August 31. The next day, the depression developed into a tropical storm, receiving the name Larry. The storm moved quickly across the far eastern tropical Atlantic, where it strengthened into a Category 1 hurricane the morning of September 2. Then, after undergoing a period of rapid intensification, Larry became a major Category 3 hurricane early on September 4. After churning for several days as a strong hurricane in the open ocean, Larry made landfall in Newfoundland on September 11, as a Category 1 hurricane. Later that day, Larry became an extratropical cyclone. Finally, on September 13, Larry was absorbed by a larger extratropical cyclone near Greenland.
References
- ↑ Fritzen, Robert; Lang, Victoria; Gensini, Vittorio A. (2021). "Trends and Variability of North American Cool-Season Extratropical Cyclones: 1979–2019". Journal of Applied Meteorology and Climatology. 60 (9): 1319–1331. Bibcode:2021JApMC..60.1319F. doi:10.1175/JAMC-D-20-0276.1. S2CID 238706988 . Retrieved 13 December 2021.
