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.
Tropical Storm Zeta was a very late-developing tropical storm that formed in the central Atlantic Ocean during the 2005 Atlantic hurricane season, one month after the season's official end. Becoming a tropical depression on December 30, and intensifying the following day into the season's 28th storm, Zeta continued into January 2006. It was one of only two Atlantic tropical cyclones to span two calendar years.
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 2012 Pacific hurricane season was a moderately active Pacific hurricane season that saw an unusually high number of tropical cyclones pass west of the Baja California Peninsula. The season officially began on May 15 in the eastern Pacific Ocean, and on June 1 in the central Pacific (from 140°W to the International Date Line, north of the equator; they both ended on November 30. These dates conventionally delimit the period of each year when most tropical cyclones form in these regions of the Pacific Ocean. However, the formation of tropical cyclones is possible at any time of the year. This season's first system, Tropical Storm Aletta, formed on May 14, and the last, Tropical Storm Rosa, dissipated on November 3.
Tropical Storm Laura was a large but short-lived tropical cyclone that developed over the north-central Atlantic Ocean in late September during the 2008 Atlantic hurricane season. Laura's remnants later impacted the Netherlands, Germany, and Norway. The 12th named storm of the season, Laura formed out of a large extratropical area of low pressure located about 1,015 miles (1,633 km) west of the Azores on September 29. Laura slowly developed tropical characteristics throughout the day as it moved over warmer waters. On the afternoon of September 30, Laura had acquired enough tropical characteristics to be designated a tropical storm. Shortly after being declared tropical, Laura began to undergo an extratropical transition, which did not fully take place until the morning of October 1. Laura degenerated into a post-tropical cyclone later that morning, and the final advisory by the National Hurricane Center was issued. The remnants of Laura contributed to heavy rainfall and power outages in the British Isles, the Netherlands, and Norway on October 5 to 8.
Tropical Storm Grace holds the record for being the farthest northeast forming tropical cyclone in the Atlantic basin. The seventh named storm of the slightly below average 2009 Atlantic hurricane season, Grace formed from an extratropical cyclone over the Azores on 4 October. It strengthened to attain peak sustained winds of 65 mph (100 km/h) and developed an eye-like feature, although cold sea surface temperatures inhibited the development of thunderstorm activity near the center. The storm lost its tropical characteristics on 6 October, and the storm's remnants merged with a separate system near the British Isles on 7 October.
Hurricane Epsilon was the twenty-seventh named tropical or subtropical storm and the final of 15 hurricanes in the record-breaking 2005 Atlantic hurricane season. Originating from a cold front beneath an upper-level low, Epsilon formed on November 29 about 915 mi (1470 km) east of Bermuda, becoming the second tropical storm to do so in that area of the Atlantic within the span of a week. Initially, the National Hurricane Center (NHC) forecast the storm to transition into an extratropical cyclone within five days, due to conditions unfavorable for significant intensification. Epsilon continually defied forecasts, at first due to an unexpected loop to the southwest, and later due to retaining its strength despite cold waters and strong wind shear.
The following is a glossary of tropical cyclone terms.
The 2019 Pacific hurricane season was a near average season which produced nineteen named storms, though most were rather weak and short-lived. Only seven hurricanes formed, the fewest since 2010. The season officially began on May 15 in the East Pacific Ocean, and on June 1 in the Central Pacific; they both ended on November 30. These dates conventionally delimit the period of each year when most tropical cyclones form in the Pacific basin. This season was one of the latest-starting Pacific hurricane seasons on record, with the first tropical cyclone, Hurricane Alvin, forming on June 25. The final system, Tropical Depression Twenty-One-E, dissipated on November 18.
The 2023 Atlantic hurricane season is the current hurricane season in the Atlantic Ocean in the Northern Hemisphere. It officially began on June 1, and will end on November 30. These dates, adopted by convention, historically describe the period in each year when most tropical cyclogenesis occurs in the Atlantic. However, the formation of subtropical or tropical cyclones is possible at any time of the year, as demonstrated by the formation of a subtropical storm on January 16, the earliest start of an Atlantic hurricane season since Hurricane Alex in 2016. This system went unnamed operationally, as the National Hurricane Center (NHC) treated it as non-tropical.
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.
The 2021 Pacific hurricane season was a moderately active Pacific hurricane season, with above-average activity in terms of number of named storms, but below-average activity in terms of major hurricanes, with 17 named storms, 8 hurricanes, and 2 major hurricanes forming in all. It also had a near-normal accumulated cyclone energy (ACE). The season officially began on May 15, 2021 in the Eastern Pacific Ocean, and on June 1, 2021, in the Central Pacific in the Northern Hemisphere. The season ended in both regions on November 30, 2021. These dates historically describe the period each year when most tropical cyclogenesis occurs in these regions of the Pacific and are adopted by convention. However, the formation of tropical cyclones is possible at any time of the year, as illustrated by the formation of Tropical Storm Andres on May 9, which was the earliest forming tropical storm on record in the Eastern Pacific. Conversely, 2021 was the second consecutive season in which no tropical cyclones formed in the Central Pacific.
Tropical Storm Nestor was a large but short-lived and disorganized tropical cyclone which caused widespread tornadoes and heavy rain in the Southeastern United States during mid-October 2019. The sixteenth depression and fourteenth named storm of the erratic 2019 Atlantic hurricane season, Nestor originated from a broad area of low pressure over the Western Caribbean. It emerged in the Gulf of Mexico and began to organize slightly, becoming Potential Tropical Cyclone Sixteen due to its threat to the Southeastern United States. It gained a sufficient enough of a circulation to be designated Tropical Storm Nestor near the Florida Panhandle early on October 18, crawling to the northeast, and then finally transitioning into an extratropical cyclone due to strong shear from a nearby upper-level low before making landfall on the Florida Panhandle on October 19.
Hurricane Dolores was a powerful and moderately damaging tropical cyclone whose remnants brought record-breaking heavy rains and strong winds to California. The seventh named storm, fourth hurricane, and third major hurricane of the record-breaking 2015 Pacific hurricane season, Dolores formed from a tropical wave on July 11. The system gradually strengthened, attaining hurricane status on July 13. Dolores rapidly intensified as it neared the Baja California peninsula, finally peaking as a Category 4 hurricane on the Saffir–Simpson scale with winds of 130 mph (215 km/h) on July 15. An eyewall replacement cycle began and cooler sea-surface temperatures rapidly weakened the hurricane, and Dolores weakened to a tropical storm two days later. On July 18, Dolores degenerated into a remnant low west of the Baja California peninsula.
Hurricane Paulette was a strong and long-lived Category 2 Atlantic hurricane which became the first to make landfall in Bermuda since Hurricane Gonzalo did so in 2014. The sixteenth named storm and sixth hurricane of the record-breaking 2020 Atlantic hurricane season, Paulette developed from a tropical wave that left the coast of Africa on September 2. The wave eventually consolidated into a tropical depression on September 7. Paulette fluctuated in intensity over the next few days, due to strong wind shear, initially peaking as a strong tropical storm on September 8. It eventually strengthened into a hurricane early on September 13 as shear decreased. On September 14, Paulette made landfall in northeastern Bermuda as a Category 2 hurricane, while making a gradual turn to the northeast. The cyclone further strengthened as it moved away from the island, reaching its peak intensity with 1-minute sustained winds of 105 mph (169 km/h) and a minimum central atmospheric pressure of 965 mbar (28.5 inHg) on September 14. On the evening of September 15, Paulette began to weaken and undergo extratropical transition, which it completed on September 16. The hurricane's extratropical remnants persisted and moved southward then eastward, and eventually, Paulette regenerated into a tropical storm early on September 20 south of the Azores– which resulted in the U.S National Weather Service coining the phrase "zombie storm" to describe its unusual regeneration. Paulette's second phase proved short-lived, however, as the storm quickly weakened and became post-tropical again two days later. The remnant persisted for several days before dissipating south of the Azores on September 28. In total, Paulette was a tropical cyclone for 11.25 days, and the system had an overall lifespan of 21 days.
Subtropical Storm Alpha was the first subtropical or tropical cyclone ever observed to make landfall in mainland Portugal. The twenty-second tropical or subtropical cyclone and twenty-first named storm of the extremely active and record-breaking 2020 Atlantic hurricane season, Alpha originated from a large non-tropical low that was first monitored by the National Hurricane Center on 15 September. Initially not anticipated to transition into a tropical cyclone, the low gradually tracked south-southeastward for several days with little development. By early on 17 September, the low had separated from its frontal features and exhibited sufficient organization to be classified as a subtropical cyclone, as it approached the Iberian Peninsula, becoming a subtropical storm around that time. Alpha then made landfall just south of Figueira da Foz, Portugal during the evening of 18 September, then rapidly weakened as it moved over the mountainous terrain of Northeastern Portugal. The system degenerated into a remnant low on 19 September, when it was last noted.
Tropical Storm Beta was a tropical cyclone that brought heavy rainfall, flooding, and severe weather to the Southeastern United States in September 2020. The twenty-third tropical depression and twenty-third named storm of the record-breaking 2020 Atlantic hurricane season, Beta originally formed from a trough of low pressure that developed in the northeastern Gulf of Mexico on September 10. The low moved slowly southwestward, with development hampered initially by the development of nearby Hurricane Sally. After Sally moved inland over the Southeastern United States and weakened, the disturbance became nearly stationary in the southwestern Gulf, where it began to organize. By September 16, the storm had gained a low-level circulation center and had enough organization to be designated as Tropical Depression Twenty-Two. The system held its intensity for a day due to the influence of strong wind shear and dry air, before eventually attaining tropical storm strength. It slowly moved northward and intensified to a mid-range tropical storm before dry air and wind shear halted its intensification. Beta then became nearly stationary on September 19, before starting to move west towards the Texas coast the next day, weakening as it approached. On September 21, Beta made landfall near Matagorda Peninsula, Texas as a minimal tropical storm. It subsequently weakened to a tropical depression the next day before becoming post-tropical early on September 23. Its remnants moved northeastward, before the center elongated and merged with a cold front early on September 25.
Tropical Storm Melissa was a nor'easter and a short-lived tropical storm that affected portions of the U.S. East Coast and Atlantic Canada in October 2019. The fourteenth depression and thirteenth named storm of the 2019 Atlantic hurricane season, Melissa originated from a cold front that developed over the southwestern Atlantic on October 6. The system developed tropical storm-force winds on October 8, before becoming a nor'easter on the next day. The system then began to organize, and was designated as Subtropical Storm Melissa on October 11. Melissa was then upgraded into a tropical storm, the following day. However, the storm soon began to disorganize and transition into an extratropical low by October 14, before dissipating later that same day.
