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.
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 2005 Pacific hurricane season was a near-average season which produced fifteen named storms, only seven hurricanes formed and two major hurricanes. It was also the second consecutive season in which no tropical cyclone of at least tropical storm intensity made landfall. The season officially began on May 15 in the East Pacific Ocean, and on June 1 in the Central Pacific; they ended on November 30. These dates conventionally delimit the period of each year when most tropical cyclones form in the Pacific basin. However, the formation of tropical cyclones is possible at any time of the year.
The 2001 Pacific hurricane season was a relatively near-average Pacific hurricane season which produced sixteen named storms, though most were rather weak and short-lived including one unnamed tropical storm which was operationally recognized as a tropical depression, the first such occurrence since 1996. Only eight hurricanes formed and two major hurricanes. The season officially began on May 15 in the East Pacific Ocean, and on June 1 in the Central Pacific; they ended on November 30. These dates conventionally delimit the period of each year when most tropical cyclones form in the Pacific basin. However, the formation of tropical cyclones is possible at any time of the year.
This is a list of meteorology topics. The terms relate to meteorology, the interdisciplinary scientific study of the atmosphere that focuses on weather processes and forecasting.
The 1990 Pacific hurricane season was a very active season which observed 21 named storms within the basin. The season also produced the fourth highest ACE index value on record. The season was officially started on May 15 in the eastern Pacific, and on June 1 in the central Pacific, and lasted until November 30. These dates conventionally delimit the period of each year when most tropical cyclones form in the northeastern Pacific Ocean. However, the formation of tropical cyclones is possible at any time of the year, as illustrated in 1990 by the formation of the season's first named storm, Hurricane Alma, on May 12. At the time, this was the earliest formation of a tropical storm on record in the eastern Pacific
A mesoscale convective system (MCS) is a complex of thunderstorms that becomes organized on a scale larger than the individual thunderstorms but smaller than extratropical cyclones, and normally persists for several hours or more. A mesoscale convective system's overall cloud and precipitation pattern may be round or linear in shape, and include weather systems such as tropical cyclones, squall lines, lake-effect snow events, polar lows, and mesoscale convective complexes (MCCs), and generally forms near weather fronts. The type that forms during the warm season over land has been noted across North and South America, Europe, and Asia, with a maximum in activity noted during the late afternoon and evening hours.
The 2007 Atlantic hurricane season was the first season since 2003 to feature tropical activity both before and after the official bounds of the season. There were an above-average number of named storms during the season – 15, however many storms were weak and short-lived. Despite the predominance of weak systems, this was the first season on record to feature more than one Category 5 landfalling hurricane. This would not happen again until 2017. It produced 17 tropical cyclones, 15 tropical storms, six hurricanes, and two major hurricanes. It officially started on June 1 and ended on November 30, dates which conventionally delimit the period during which most tropical cyclones form in the Atlantic Ocean, although as shown by Subtropical Storm Andrea and Tropical Storm Olga in early May and early December, respectively, the formation of tropical cyclones is possible at any time of the year. The first system, Subtropical Storm Andrea, developed on May 9, while the last storm, Tropical Storm Olga, dissipated on December 13. The most intense hurricane, Dean, was, at the time, the third most intense landfalling Atlantic storm on record. It was the second on record in which an Atlantic hurricane, Felix, and an eastern Pacific hurricane, Henriette, made landfall on the same day. September had a then record-tying eight storms, until it was surpassed in 2020. However, the strengths and durations of most of the storms were low.
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.
The 2007 Pacific hurricane season was a well below-average Pacific hurricane season, featuring only one major hurricane. The season officially started on May 15 in the eastern Pacific and on June 1 in the central Pacific, and ended on November 30; these dates conventionally delimit the period during which most tropical cyclones form in the region. The first tropical cyclone of the season, Alvin, developed on May 27, while the final system of the year, Kiko, dissipated on October 23. Due to unusually strong wind shear, activity fell short of the long-term average, with a total of 11 named storms, 4 hurricanes, and 1 major hurricane. At the time, 2007 featured the second-lowest value of the Accumulated cyclone energy (ACE) index since reliable records began in 1971. Two tropical cyclones – Cosme and Flossie – crossed into the central Pacific basin during the year, activity below the average of 4 to 5 systems.
Tropical cyclogenesis is the development and strengthening of a tropical cyclone in the atmosphere. The mechanisms through which tropical cyclogenesis occurs are distinctly different from those through which temperate cyclogenesis occurs. Tropical cyclogenesis involves the development of a warm-core cyclone, due to significant convection in a favorable atmospheric environment.
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 2008 Pacific hurricane season was a near-average Pacific hurricane season which featured seventeen named storms, though most were rather weak and short-lived. Only seven hurricanes formed and two major hurricanes. This season was also the first since 1996 to have no cyclones cross into the central Pacific. The season officially began on May 15 in the eastern Pacific and on June 1 in the central Pacific. It ended in both regions on November 30. These dates, adopted by convention, historically describe the period in each year when most tropical cyclone formation occurs in these regions of the Pacific. This season, the first system, Tropical Storm Alma, formed on May 29, and the last, Tropical Storm Polo, dissipated on November 5.
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.
The 2006 Pacific hurricane season was the first above-average season since 1997 which produced twenty-five tropical cyclones, with nineteen named storms, though most were rather weak and short-lived. Only eleven hurricanes formed and six major hurricanes. Following the inactivity of the previous seasons, forecasters predicted that season would be only slightly above active. It was also the first time since 2003 in which at least one cyclone of tropical storm intensity made landfall. The season officially began on May 15 in the East Pacific Ocean, and on June 1 in the Central Pacific; they ended on November 30. These dates conventionally delimit the period of each year when most tropical cyclones form in the Pacific basin. However, the formation of tropical cyclones is possible at any time of the year.
The 2012 Atlantic hurricane season was the final year in a consecutive string of three very active seasons since 2010, with 19 tropical storms; although many of the storms were weak and short-lived. The 2012 season was also a costly season in terms of property damage, and remains the fifth-costliest season, behind 2021, 2022, 2005 and 2017. The season officially began on June 1 and ended on November 30, dates that conventionally delimit the period during each year in which most tropical cyclones form in the Atlantic Ocean. However, Alberto, the first named system of the year, developed on May 19 – the earliest date of formation since Subtropical Storm Andrea in 2007. A second tropical cyclone, Beryl, developed later that month. This was the first occurrence of two pre-season named storms in the Atlantic basin since 1951. It moved ashore in North Florida on May 29 with winds of 65 mph (105 km/h), making it the strongest pre-season storm to make landfall in the Atlantic basin. This season marked the first time since 2009 where no tropical cyclones formed in July. Another record was set by Hurricane Nadine later in the season; the system became the fourth-longest-lived tropical cyclone ever recorded in the Atlantic, with a total duration of 22.25 days. The final storm to form, Tony, dissipated on October 25 – however, Hurricane Sandy, which formed before Tony, became extratropical on October 29.
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 Atlantic hurricane season was the fourth consecutive above-average and damaging season dating back to 2016. However, many storms were weak and short-lived, especially towards the end of the season. Six of those named storms achieved hurricane status, while three intensified into major hurricanes. Two storms became Category 5 hurricanes, marking the fourth consecutive season with at least one Category 5 hurricane, the third consecutive season to feature at least one storm making landfall at Category 5 intensity, and the seventh on record to have multiple tropical cyclones reaching Category 5 strength. The season officially began on June 1 and ended on November 30. These dates historically describe the period each year when most tropical cyclones form in the Atlantic basin and are adopted by convention. However, tropical cyclogenesis is possible at any time of the year, as demonstrated by the formation of Subtropical Storm Andrea on May 20, making this the fifth consecutive year in which a tropical or subtropical cyclone developed outside of the official season.
The 2020 Pacific hurricane season was the least active Pacific hurricane season since 2011. Altogether, 21 tropical cyclones developed. The season was near average in terms of tropical storms, featuring a total of 17, but had a well below average number of hurricanes and major hurricanes, with only 4 hurricanes and 3 major hurricanes forming. Additionally, no tropical cyclones formed in the Central Pacific basin for the first time since 2017, marking the start of a series of seasons with no tropical cyclogenesis occurring there. The season officially began on May 15 in the East 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 the respective regions. However, the formation of tropical cyclones is possible at any time of the year, as illustrated in 2020 by the formation of the season's first system, Tropical Depression One-E, on April 25. This the earliest formation of a tropical cyclone on record in the eastern Pacific basin proper.
