Azores High

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The Azores High (Portuguese : Anticiclone dos Açores) also known as North Atlantic (Subtropical) High/Anticyclone or the Bermuda-Azores High, is a large subtropical semi-permanent centre of high atmospheric pressure typically found south of the Azores in the Atlantic Ocean, at the Horse latitudes. It forms one pole of the North Atlantic oscillation, the other being the Icelandic Low. The system influences the weather and climatic patterns of vast areas of North Africa and southern Europe, and to a lesser extent, eastern North America. The aridity of the Sahara Desert and the summer drought of the Mediterranean Basin is due to the large-scale subsidence and sinking motion of air in the system. In its summer position (the Bermuda High), the high is centered near Bermuda, and creates a southwest flow of warm tropical air toward the East Coast of the United States. In summer, the Azores-Bermuda High is strongest. The central pressure hovers around 1024 mbar (hPa).

Contents

This high-pressure block exhibits anticyclonic nature, circulating the air clockwise. Due to this direction of movement, African eastern waves are impelled along the southern periphery of the Azores High away from coastal West Africa towards the Caribbean, Central America, or the Bahamas, favouring tropical cyclogenesis, especially during the hurricane season.

Tropical wave formation on the Atlantic Ocean. Tropical waves.jpg
Tropical wave formation on the Atlantic Ocean.

Variations

Research into global warming suggests that it may be intensifying the Bermuda High in some years, independently of oscillations such as ENSO, leading to more precipitation extremes across the Southeastern United States. Latitudinal displacement of the ridge is also occurring, and computer models depict more westward expansion of the anticyclone in the future. [1] [2] However, during the winter of 20092010, the Azores High was smaller, displaced to the northeast and weaker than usual, allowing sea surface temperatures in the Central Atlantic to increase quickly. [3]

See also

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South Atlantic tropical cyclone unusual weather event originating in the South Atlantic Ocean

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1963 Atlantic hurricane season hurricane season in the Atlantic Ocean

The 1963 Atlantic hurricane season featured one of the deadliest tropical cyclones on record in the Atlantic basin: Hurricane Flora. The season officially began on June 15, and lasted until November 15. These dates conventionally delimit the period of each year when most tropical cyclones form in the Atlantic basin. It was a near-average season in terms of tropical storms, with a total of nine named storms. The first system, Hurricane Arlene, developed between Cape Verde and the Lesser Antilles on July 31. The storm later impacted Bermuda, where strong winds resulted in about $300,000 (1963 USD) in damage. Other storms such as hurricanes Beulah and Debra, as well as an unnamed tropical storm, did not impact land. During the month of September, Hurricane Cindy caused wind damage and flooding in Texas, leaving three deaths and approximately $12.5 million in damage. Hurricane Edith passed through the Lesser Antilles and the eastern Greater Antilles, causing 10 deaths and about $43 million in damage, most of which occurred on Martinique.

1973 Atlantic hurricane season hurricane season in the Atlantic Ocean

The 1973 Atlantic hurricane season was the first season to use the Saffir–Simpson hurricane scale, a scale developed in 1971 by Herbert Saffir and Robert Simpson to rate the intensity of tropical cyclones. The season produced 24 tropical and subtropical cyclones, of which only 8 reached storm intensity, 4 became hurricanes, and only 1 reached major hurricane status. Although more active than the 1972 season, 1973 brought few storms of note. Nearly half of the season's storms affected land, one of which resulted in severe damage.

1975 Atlantic hurricane season hurricane season in the Atlantic Ocean

The 1975 Atlantic hurricane season featured the first tropical storm to be upgraded to a hurricane based solely on satellite imagery – Hurricane Doris. The season officially began on June 1 and lasted until November 30. These dates conventionally delimit the period of each year when most tropical cyclones form in the Atlantic basin. The season was near average, with nine tropical storms forming, of which six became hurricanes. Three of those six became major hurricanes, which are Category 3 or higher on the Saffir–Simpson scale. The first system, Tropical Depression One, developed on June 24. Tropical Storm Amy in July caused minor beach erosion and coastal flooding from North Carolina to New Jersey, and killed one person when a ship capsized offshore North Carolina. Hurricane Blanche brought strong winds to portions of Atlantic Canada, leaving about $6.2 million (1975 USD) in damage. Hurricane Caroline brought high tides and flooding to northeastern Mexico and Texas, with two drownings in the latter.

1976 Atlantic hurricane season hurricane season in the Atlantic Ocean

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1978 Atlantic hurricane season hurricane season in the Atlantic Ocean

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1979 Atlantic hurricane season hurricane season in the Atlantic Ocean

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1991 Atlantic hurricane season Summary of the relevant tropical storms

The 1991 Atlantic hurricane season was the first season since 1984 in which no hurricanes developed from tropical waves, which are the source for most North Atlantic tropical cyclones. The hurricane season officially began on June 1, and ended on November 30. It was the least active in four years due to higher than usual wind shear across the Atlantic Ocean. The first storm, Ana, developed on July 2 off the southeast United States and dissipated without causing significant effects. Two other tropical storms in the season – Danny and Erika – did not significantly affect land. Danny dissipated east of the Lesser Antilles, and Erika passed through the Azores before becoming extratropical. In addition, there were four non-developing tropical depressions. The second depression of the season struck Mexico with significant accompanying rains.

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A tropical wave, in and around the Atlantic Ocean, is a type of atmospheric trough, an elongated area of relatively low air pressure, oriented north to south, which moves from east to west across the tropics, causing areas of cloudiness and thunderstorms. Tropical waves form in the easterly flow along the equatorward side of the subtropical ridge or belt of high air pressure which lies north and south of the Intertropical Convergence Zone (ITCZ). Tropical waves are generally carried westward by the prevailing easterly winds along the tropics and subtropics near the equator. They can lead to the formation of tropical cyclones in the north Atlantic and northeastern Pacific basins. A tropical wave study is aided by Hovmöller diagrams, a graph of meteorological data.

Hurricane Faith Category 3 Atlantic hurricane in 1966

Hurricane Faith reached the northernmost latitude and had the longest track of any Atlantic tropical cyclone. The sixth named storm and fifth hurricane of the 1966 Atlantic hurricane season, Faith developed from an area of disturbed weather between Cape Verde and the west coast of Africa on August 21. Tracking westward, the depression gradually intensified and became Tropical Storm Faith on the following day. Moving westward across the Atlantic Ocean, it continued to slowly strengthen, reaching hurricane status early on August 23. About 42 hours later, Faith reached an initial peak with winds of 105 mph (165 km/h), before weakening slightly on August 26. Located near the Lesser Antilles, the outer bands of Faith produced gale force winds in the region, especially Puerto Rico, the Virgin Islands, and Antigua. Minor coastal damage occurred as far south as Trinidad and Tobago.

1950 Atlantic hurricane season hurricane season in the Atlantic Ocean

The 1950 Atlantic hurricane season was the first year in the Atlantic hurricane database (HURDAT) that storms were given names in the Atlantic basin. Names were taken from the Joint Army/Navy Phonetic Alphabet, with the first named storm being designated "Able", the second "Baker", and so on. It was an active season with sixteen tropical storms, with eleven of them developing into hurricanes. Six of these hurricanes were intense enough to be classified as major hurricanes—a denomination reserved for storms that attained sustained winds equivalent to a Category 3 or greater on the present-day Saffir–Simpson scale. One storm, the twelfth of the season, was unnamed and was originally excluded from the yearly summary, and three additional storms were discovered in re-analysis. The large quantity of strong storms during the year yielded, prior to modern reanalysis, what was the highest seasonal accumulated cyclone energy (ACE) of the 20th century in the Atlantic basin; 1950 held the seasonal ACE record until broken by the 1995 Atlantic hurricane season. However, later examination by researchers determined that several storms in the 1950 season were weaker than thought, leading to a lower ACE than assessed originally.

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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 heavy 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.

Hurricane Arlene (1987) Category 1 Atlantic hurricane in 1987

Hurricane Arlene was a long-lived tropical cyclone that moved eastward in an erratic fashion in the northern Atlantic Ocean in mid-August 1987. The first named storm of the 1987 Atlantic hurricane season, Arlene formed out of an area of low pressure associated with a decaying frontal system along the North Carolina coastline, Arlene tracked in a general eastward direction across the Atlantic Ocean, taking an erratic track with several curves. On August 13, the storm brushed Bermuda as a weak tropical storm before continuing out to sea. On August 20, the storm briefly stalled before becoming a hurricane two days later. Early on August 24, the storm transitioned into an extratropical cyclone over the far north Atlantic before curving southeast and dissipating near the Iberian Peninsula on August 26.

Timeline of the 2012 Atlantic hurricane season

The 2012 Atlantic hurricane season featured the third-most named storms for the third consecutive year on record. Though the season officially began on June 1 and ended on November 30, dates which conventionally delimit the period of each year when most tropical cyclones develop in the Atlantic basin, two storms – Alberto and Beryl – developed before the official start, on May 19 and May 26, respectively; this was the first such occurrence since the 1908 season. The season's final storm to form, Tony, dissipated on October 25, although the previous cyclone, Sandy, did not do so until four days later.

Hurricane Alex (2016) Category 1 Atlantic hurricane in 2016

Hurricane Alex was the first Atlantic hurricane to occur in January since Hurricane Alice in 1955. Alex originated as a non-tropical low near the Bahamas on January 7, 2016. Initially traveling northeast, the system passed by Bermuda on January 8 before turning southeast and deepening. It briefly acquired hurricane-force winds by January 10, then weakened slightly before curving towards the east and later northeast. Acquiring more tropical weather characteristics over time, the system transitioned into a subtropical cyclone well south of the Azores on January 12, becoming the first North Atlantic tropical or subtropical cyclone in January since Tropical Storm Zeta of 2006. Alex continued to develop tropical features while turning north-northeast, and transitioned into a fully tropical cyclone on January 14. The cyclone peaked in strength as a Category 1 hurricane on the Saffir–Simpson scale with maximum sustained winds of 85 mph (140 km/h) and a central pressure of 981 mbar. Alex weakened to a high-end tropical storm before making landfall on Terceira Island on January 15. By that time, the storm was losing its tropical characteristics; it fully transitioned back into a non-tropical cyclone several hours after moving away from the Azores. Alex ultimately merged with another cyclone over the Labrador Sea on January 17.

Centers of action are extensive and almost stationary low-pressure areas or anticyclones which control the movement of atmospheric disturbances over a large area. This does not mean that the position of the center is constant over a specific area but that the monthly atmospheric pressure corresponds to a high or a low pressure.

References

  1. Lucas, Tim. "Variable southeast summer rainfall linked to climate change". Duke University. EurekAlert!. Archived from the original on 30 October 2010. Retrieved 29 October 2010.
  2. Li, Wenhong; Laifang Li; Rong Fu; Yi Deng; Hui Wang (October 4, 2010). "Changes to the North Atlantic Subtropical High and Its Role in the Intensification of Summer Rainfall Variability in the Southeastern United States". Journal of Climate. 24 (5): 1499–1506. Bibcode:2011JCli...24.1499L. CiteSeerX   10.1.1.211.2720 . doi:10.1175/2010JCLI3829.1. ISSN   1520-0442.
  3. Publications, RMS. "2009 Atlantic Hurricane Season Review and 2010 Season Outlook" (PDF). Risk Management Solutions. RMS Catastrophe Response. Archived (PDF) from the original on 8 October 2010. Retrieved 29 October 2010.


Coordinates: 34°00′00″N30°00′00″W / 34.0000°N 30.0000°W / 34.0000; -30.0000