|Part of the nature series|
An Atlantic hurricane or tropical storm is a tropical cyclone that forms in the Atlantic Ocean, usually between the months of June and November. A hurricane differs from a cyclone or typhoon only on the basis of location.A hurricane is a storm that occurs in the Atlantic Ocean and northeastern Pacific Ocean, a typhoon occurs in the northwestern Pacific Ocean, and a cyclone occurs in the south Pacific or Indian Ocean.
A tropical cyclone is a rapidly rotating storm system characterized by a low-pressure center, a closed low-level atmospheric circulation, strong winds, and a spiral arrangement of thunderstorms that produce heavy rain or squalls. Depending on its location and strength, a tropical cyclone is referred to by different names, including hurricane, typhoon, tropical storm, cyclonic storm, tropical depression, and simply cyclone. A hurricane is a tropical cyclone that occurs in the Atlantic Ocean and northeastern Pacific Ocean, and a typhoon occurs in the northwestern Pacific Ocean; in the south Pacific or Indian Ocean, comparable storms are referred to simply as "tropical cyclones" or "severe cyclonic storms".
The Atlantic Ocean is the second largest of the world's oceans, with an area of about 106,460,000 square kilometers. It covers approximately 20 percent of Earth's surface and about 29 percent of its water surface area. It separates the "Old World" from the "New World".
A typhoon is a mature tropical cyclone that develops between 180° and 100°E in the Northern Hemisphere. This region is referred to as the Northwestern Pacific Basin, and is the most active tropical cyclone basin on Earth, accounting for almost one-third of the world's annual tropical cyclones. For organizational purposes, the northern Pacific Ocean is divided into three regions: the eastern, central, and western. The Regional Specialized Meteorological Center (RSMC) for tropical cyclone forecasts is in Japan, with other tropical cyclone warning centers for the northwest Pacific in Hawaii, the Philippines and Hong Kong. While the RSMC names each system, the main name list itself is coordinated among 18 countries that have territories threatened by typhoons each year.
Tropical cyclones can be categorized by intensity. Tropical storms have one-minute maximum sustained winds of at least 39 mph (34 knots, 17 m/s, 63 km/h), while hurricanes have one-minute maximum sustained winds exceeding 74 mph (64 knots, 33 m/s, 119 km/h). Most North Atlantic tropical storms and hurricanes form between June 1 and November 30. The United States National Hurricane Center monitors the basin and issues reports, watches, and warnings about tropical weather systems for the North Atlantic Basin as one of the Regional Specialized Meteorological Centers for tropical cyclones, as defined by the World Meteorological Organization.
The United States of America (USA), commonly known as the United States or America, is a country comprising 50 states, a federal district, five major self-governing territories, and various possessions. At 3.8 million square miles, the United States is the world's third or fourth largest country by total area and is slightly smaller than the entire continent of Europe. With a population of over 327 million people, the U.S. is the third most populous country. The capital is Washington, D.C., and the most populous city is New York City. Most of the country is located contiguously in North America between Canada and Mexico.
The National Hurricane Center (NHC) is the division of the United States' NOAA/National Weather Service responsible for tracking and predicting tropical weather systems between the Prime Meridian and the 140th meridian west poleward to the 30th parallel north in the northeast Pacific Ocean and the 31st parallel north in the northern Atlantic Ocean. The agency, which is co-located with the Miami branch of the National Weather Service, is situated on the campus of Florida International University in University Park, Florida.
The World Meteorological Organization is an intergovernmental organization with a membership of 193 Member States and Territories. The President of the World Meteorological Congress, its supreme body, is Gerhard Adrian as a successor of David Grimes. The Organization is headquartered in Geneva, Switzerland.
In recent times, tropical disturbances that reach tropical storm intensity are named from a predetermined list. Hurricanes that result in significant damage or casualties may have their names retired from the list at the request of the affected nations in order to prevent confusion should a subsequent storm be given the same name.On average, in the North Atlantic basin (from 1966 to 2009) 11.3 named storms occur each season, with an average of 6.2 becoming hurricanes and 2.3 becoming major hurricanes (Category 3 or greater). The climatological peak of activity is around September 10 each season.
Climatology or climate science is the scientific study of climate, scientifically defined as weather conditions averaged over a period of time. This modern field of study is regarded as a branch of the atmospheric sciences and a subfield of physical geography, which is one of the Earth sciences. Climatology now includes aspects of oceanography and biogeochemistry.
In March 2004, Catarina was the first hurricane-intensity tropical cyclone ever recorded in the Southern Atlantic Ocean. Since 2011, the Brazilian Navy Hydrographic Center has started to use the same scale of the North Atlantic Ocean for tropical cyclones in the South Atlantic Ocean and assign names to those which reach 35 kn (65 km/h; 40 mph).
Hurricane Catarina or Cyclone Catarina was an extremely rare South Atlantic tropical cyclone that hit Southern Brazil in late March 2004. The storm developed out of a stationary cold-core upper-level trough on March 12. Almost a week later, on March 19, a disturbance developed along the trough and traveled towards the east-southeast until March 22 when a ridge stopped the forward motion of the disturbance. The disturbance was in an unusually favorable environment with a slightly below-average wind shear and above-average sea surface temperatures. The combination of the two led to a slow transition from an extratropical cyclone to a subtropical cyclone by March 24. The storm continued to obtain tropical characteristics and became a tropical storm the next day while the winds steadily increased. The storm attained wind speeds of 75 mph (120 km/h)—equivalent to a low-end Category 1 hurricane on the Saffir–Simpson scale—on March 26. At that time, it was unofficially named Catarina and was also the first hurricane-strength tropical cyclone ever recorded in the Southern Atlantic Ocean. Unusually favorable conditions persisted and Catarina continued to intensify, and was estimated to have peaked with 1-minute sustained winds of 100 mph (155 km/h) on March 28. The center of the storm made landfall between the cities of Passo de Torres and Balneário Gaivota, Santa Catarina. Catarina rapidly weakened upon landfall and dissipated later that day.
The Brazilian Navy is the naval service branch of the Brazilian Armed Forces, responsible for conducting naval operations. The Brazilian Navy is the largest navy in South America and in Latin America, and the second largest navy in the Americas, after the United States Navy.
Tropical cyclones are steered by the surrounding flow throughout the depth of the troposphere (the atmosphere from the surface to about eight miles (12 km) high). Neil Frank, former director of the United States National Hurricane Center, used the analogies such as "a leaf carried along in a stream" or a "brick moving through a river of air" to describe the way atmospheric flow affects the path of a hurricane across the ocean. Specifically, air flow around high pressure systems and toward low pressure areas influences hurricane tracks.
The troposphere is the lowest layer of Earth's atmosphere, and is also where nearly all weather conditions take place. It contains approximately 75% of the atmosphere's mass and 99% of the total mass of water vapour and aerosols. The average height of the troposphere is 18 km in the tropics, 17 km in the middle latitudes, and 6 km in the polar regions in winter. The total average height of the troposphere is 13 km.
Neil Laverne Frank is an American meteorologist and former director of the National Hurricane Center (NHC) in Florida. He was instrumental in advancing both the scientific and informational aspects of hurricane forecasting. He retired in 2008 as Chief Meteorologist at KHOU-TV in Houston.
In science and engineering the study of high pressure examines its effects on materials and the design and construction of devices, such as a diamond anvil cell, which can create high pressure. By high pressure is usually meant pressures of thousands (kilobars) or millions (megabars) of times atmospheric pressure.
In the tropical latitudes, tropical storms and hurricanes generally move westward with a slight tendency toward the north, under the influence of the subtropical ridge , a high pressure system that usually extends east-west across the subtropics.South of the subtropical ridge, surface easterly winds (blowing from east to west) prevail. If the subtropical ridge is weakened by an upper trough, a tropical cyclone may turn poleward and then recurve, or curve back toward the northeast into the main belt of the Westerlies. Poleward (north) of the subtropical ridge, westerly winds prevail and generally steer tropical cyclones that reach northern latitudes toward the east. The westerlies also steer extratropical cyclones with their cold and warm fronts from west to east.
The tropics are the region of the Earth surrounding the Equator. They are delimited in latitude by the Tropic of Cancer in the Northern Hemisphere at 23°26′12.2″ (or 23.43673°) N and the Tropic of Capricorn in the Southern Hemisphere at 23°26′12.2″ (or 23.43673°) S; these latitudes correspond to the axial tilt of the Earth. The tropics are also referred to as the tropical zone and the torrid zone. The tropics include all the areas on the Earth where the Sun contacts a point directly overhead at least once during the solar year - thus the latitude of the tropics is roughly equal to the angle of the Earth's axial tilt.
A trough is an elongated (extended) region of relatively low atmospheric pressure, often associated with fronts. Troughs may be at the surface, or aloft, or both under various conditions. Most troughs bring clouds, showers, and a wind shift, particularly following the passage of the trough. This results from convergence or "squeezing" which forces lifting of moist air behind the trough line.
The westerlies, anti-trades, or prevailing westerlies, are prevailing winds from the west toward the east in the middle latitudes between 30 and 60 degrees latitude. They originate from the high-pressure areas in the horse latitudes and trend towards the poles and steer extratropical cyclones in this general manner. Tropical cyclones which cross the subtropical ridge axis into the westerlies recurve due to the increased westerly flow. The winds are predominantly from the southwest in the Northern Hemisphere and from the northwest in the Southern Hemisphere.
|Most intense Atlantic hurricanes|
Generally speaking, the intensity of a tropical cyclone is determined by either the storm's maximum sustained winds or lowest barometric pressure. The following table lists the most intense Atlantic hurricanes in terms of their lowest barometric pressure. In terms of wind speed, Hurricane Allen (in 1980) was the strongest Atlantic tropical cyclone on record, with maximum sustained winds of 190 mph (305 km/h). However, these measurements are suspect since instrumentation used to document wind speeds at the time would likely succumb to winds of such intensity. Nonetheless, their central pressures are low enough to rank them among the strongest recorded Atlantic hurricanes.
Owing to their intensity, the strongest Atlantic hurricanes have all attained Category 5 classification. Hurricane Opal, the strongest Category 4 hurricane recorded, intensified to reach a minimum pressure of 916 mbar (hPa; 27.05 inHg), a pressure typical of Category 5 hurricanes. Nonetheless, the pressure remains too high to list Opal as one of the ten strongest Atlantic tropical cyclones. Presently, Hurricane Wilma is the strongest Atlantic hurricane ever recorded, after reaching an intensity of 882 mbar (hPa; 26.05 inHg) in October 2005; this also made Wilma the strongest tropical cyclone worldwide outside of the West Pacific, where seven tropical cyclones have been recorded to intensify to lower pressures. However, this was later superseded by Hurricane Patricia in 2015 in the east Pacific, which had a pressure reading of 872 mbar. Preceding Wilma is Hurricane Gilbert, which had also held the record for most intense Atlantic hurricane for 17 years. The 1935 Labor Day hurricane, with a pressure of 892 mbar (hPa; 26.34 inHg), is the third strongest Atlantic hurricane and the strongest documented tropical cyclone prior to 1950. Since the measurements taken during Wilma and Gilbert were documented using dropsonde, this pressure remains the lowest measured over land.
Hurricane Rita is the fourth strongest Atlantic hurricane in terms of barometric pressure and one of three tropical cyclones from 2005 on the list, with the others being Wilma and Katrina at first and seventh respectively. mbar (hPa; 26.43 inHg), Rita is the strongest tropical cyclone ever recorded in the Gulf of Mexico. Mitch and Dean share intensities for the eighth strongest Atlantic hurricane at 905 mbar (hPa; 26.73 inHg). The tenth place for most intense Atlantic tropical cyclone is Hurricane Maria listed to have deepened to a pressure as low as 908 mbar (hPa; 26.81 inHg).However, with a barometric pressure of 895
Many of the strongest recorded tropical cyclones weakened prior to their eventual landfall or demise. However, three of the storms remained intense enough at landfall to be considered some of the strongest landfalling hurricanes – three of the eleven hurricanes on the list constitute the three most intense Atlantic landfalls in recorded history. The 1935 Labor Day hurricane made landfall at peak intensity, making it the most intense Atlantic landfall. Though it weakened slightly before its eventual landfall on the Yucatán Peninsula, Hurricane Gilbert maintained a pressure of 900 mbar (hPa; 26.58 inHg) at landfall, as did Camille, making their landfalls tied as the second strongest. Similarly, Hurricane Dean made landfall on the peninsula, though it did so at peak intensity and with a higher barometric pressure; its landfall marked the fourth strongest in Atlantic hurricane history.
|Total and Average Number of |
Tropical Storms by Month (1851–2017)
|Month||Total||Average per year|
|January — April||7||<0.05|
|Source: NOAA FAQ|
Climatology does serve to characterize the general properties of an average season and can be used as one of many other tools for making forecasts. Most storms form in warm waters several hundred miles north of the equator near the Intertropical convergence zone from tropical waves. The Coriolis force is usually too weak to initiate sufficient rotation near the equator. 26.5 °C (79.7 °F).Storms frequently form in the warm waters of the Gulf of Mexico, the Caribbean Sea, and the tropical Atlantic Ocean as far east as the Cape Verde Islands, the origin of strong and long-lasting Cape Verde-type hurricanes. Systems may also strengthen over the Gulf Stream off the coast of the eastern United States, wherever water temperatures exceed
Although most storms are found within tropical latitudes, occasionally storms will form further north and east from disturbances other than tropical waves such as cold fronts and upper-level lows. These are known as baroclinically induced tropical cyclones.There is a strong correlation between Atlantic hurricane activity in the tropics and the presence of an El Niño or La Niña in the Pacific Ocean. El Niño events increase the wind shear over the Atlantic, producing a less-favorable environment for formation and decreasing tropical activity in the Atlantic basin. Conversely, La Niña causes an increase in activity due to a decrease in wind shear.
According to the Azores High hypothesis by Kam-biu Liu, an anti-phase pattern is expected to exist between the Gulf of Mexico coast and the North American Atlantic coast. During the quiescent periods (3000–1400 BC, and 1000 AD to present), a more northeasterly position of the Azores High would result in more hurricanes being steered toward the Atlantic coast. During the hyperactive period (1400 BC to 1000 AD), more hurricanes were steered towards the Gulf coast as the Azores High was shifted to a more southwesterly position near the Caribbean.Such a displacement of the Azores High is consistent with paleoclimatic evidence that shows an abrupt onset of a drier climate in Haiti around 3200 14C years BP, and a change towards more humid conditions in the Great Plains during the late-Holocene as more moisture was pumped up the Mississippi Valley through the Gulf coast. Preliminary data from the northern Atlantic coast seem to support the Azores High hypothesis. A 3000-year proxy record from a coastal lake in Cape Cod suggests that hurricane activity has increased significantly during the past 500–1000 years, just as the Gulf coast was amid a quiescent period of the last millennium.
Climatologically speaking, approximately 97 percent of tropical cyclones that form in the North Atlantic develop between the dates of June 1 and November 30 – dates which delimit the modern-day Atlantic hurricane season. Though the beginning of the annual hurricane season has historically remained the same, the official end of the hurricane season has shifted from its initial date of October 31. Regardless, on average once every few years a tropical cyclone develops outside the limits of the season; as of January 2016 there have been 68 tropical cyclones in the off-season, with the most recent being Subtropical Storm Andrea in 2019. The first tropical cyclone of the 1938 Atlantic hurricane season, which formed on January 3, became the earliest forming tropical storm and hurricane after reanalysis concluded on the storm in December 2012.
Hurricane Able in 1951 was initially thought to be the earliest forming major hurricane – a tropical cyclone with winds exceeding 115 mph (185 km/h) – however following post-storm analysis it was determined that Able only reached Category 1 strength which made Hurricane Alma of 1966 the new record holder; as it became a major hurricane on June 8. Though it developed within the bounds of the Atlantic hurricane season, Hurricane Audrey in 1957 became the earliest developing Category 4 hurricane on record after it reached the intensity on June 27. However, reanalysis from 1956 to 1960 by NOAA downgraded Audrey to a Category 3, making Hurricane Dennis of 2005 the earliest Category 4 on record on July 8, 2005. The earliest-forming Category 5 hurricane, Emily, reached the highest intensity on the Saffir–Simpson hurricane wind scale on July 17, 2005.
Though the official end of the Atlantic hurricane season occurs on November 30, the dates of October 31 and November 15 have also historically marked the official end date for the hurricane season. December, the only month of the year after the hurricane season, has featured the cyclogenesis of fourteen tropical cyclones. Tropical Storm Zeta in 2005 was the latest tropical cyclone to attain tropical storm intensity as it did so on December 30. However, the second Hurricane Alice in 1954 was the latest forming tropical cyclone to attain hurricane intensity. Both Zeta and Alice were the only two storms to exist in two calendar years – the former from 1954 to 1955 and the latter from 2005 to 2006. No storms have been recorded to exceed Category 1 hurricane intensity in December. In 1999, Hurricane Lenny reached Category 4 intensity on November 17 as it took an unprecedented west to east track across the Caribbean; its intensity made it the latest developing Category 4 hurricane, though this was well within the bounds of the hurricane season. Hurricane Hattie (October 27 – November 1, 1961) was initially thought to have been the latest forming Category 5 hurricane ever documented, though reanalysis indicated that a devastating hurricane in 1932 reached such an intensity at a later date. Consequently, this made the hurricane the latest developing tropical cyclone to reach all four Saffir–Simpson hurricane wind scale classifications past Category 1 intensity.
The beginning of the hurricane season is most closely related to the timing of increases in sea surface temperatures, convective instability, and other thermodynamic factors. years. Tropical systems usually form in the Gulf of Mexico or off the east coast of the United States.Although June marks the beginning of the hurricane season, generally little activity occurs during the month with an average of 1 tropical cyclone every 2
Since 1851, a total of 81 tropical storms and hurricanes formed in the month of June. During this period, two of these systems developed in the deep tropics east of the Lesser Antilles.Since 1870, three major hurricanes have formed during June, most notably Hurricane Audrey in 1957. Audrey attained an intensity greater than that of any Atlantic tropical cyclone during June or July until Hurricanes Dennis and Emily of 2005. The easternmost forming storm during June, Tropical Storm Ana in 1979, formed at 45°W.
Not much tropical activity occurs during the month of July, but the majority of hurricane seasons see the formation of one tropical cyclone during July. From an average of Atlantic tropical cyclone seasons from 1944 to 1996, the first tropical storm in half of the seasons occurred by 11 July, and a second formed by 8 August.
Formation usually occurs in the eastern Caribbean Sea around the Lesser Antilles, in the northern and eastern parts of the Gulf of Mexico, in the vicinity of the northern Bahamas, and off the coast of The Carolinas and Virginia over the Gulf Stream. Storms travel westward through the Caribbean and then either move towards the north and curve near the eastern coast of the United States or stay on a north-westward track and enter the Gulf of Mexico.
Since 1851, a total of 105 tropical storms have formed during the month of July.Since 1870, ten of these storms reached major hurricane intensity. Only Hurricane Emily of 2005, the strongest July tropical cyclone in the Atlantic basin, attained Category 5 hurricane status during July, making it the earliest Category 5 hurricane on record. The easternmost forming storm and longest lived during the month of July, Hurricane Bertha in 2008, formed at 22.9°W and lasted 17 days.
Decrease in wind shear from July to August contributes to a significant increase of tropical activity.An average of 2.8 Atlantic tropical storms develop annually in August. On average, four named tropical storms, including one hurricane, occur by August 30, and the first intense hurricane develops by 4 September.
The peak of the hurricane season occurs in September and corresponds with low wind shearand the warmest sea surface temperatures. The month of September sees an average of 3 storms a year. By 24 September, the average Atlantic season features 7 named tropical storms, including 4 hurricanes. In addition, two major hurricanes occur on average by 28 September. Relatively few tropical cyclones make landfall at these intensities.
The favorable conditions found during September begin to decay in October. The main reason for the decrease in activity is increasing wind shear, although sea surface temperatures are also cooler than in September.Activity falls markedly with 1.8 cyclones developing on average despite a climatological secondary peak around 20 October. By 21 October, the average season features 9 named storms with 5 hurricanes. A third major hurricane occurs after 28 September in half of all Atlantic tropical cyclone seasons. In contrast to mid-season activity, the mean locus of formation shifts westward to the Caribbean and Gulf of Mexico, reversing the eastward progression of June through August.
Wind shear from westerlies increases substantially through November, generally preventing cyclone formation.On average, one tropical storm forms during every other November. On rare occasions, a major hurricane occurs. The few intense hurricanes in November include Hurricane "Cuba" in late October and early November 1932 (the strongest November hurricane on record peaking as a Category 5 hurricane), Hurricane Lenny in mid-November 1999, Hurricane Kate in late November 1985 which was the latest major hurricane formation on record until Hurricane Otto (a category 3 storm) of the 2016 hurricane season. Hurricane Paloma was a very potent category 4 storm that made landfall in Cuba in early November 2008.
Although the hurricane season is defined as beginning on June 1 and ending on November 30, there have been several off-season storms. Since 1870, there have been 32 off-season cyclones, 18 of which occurred in May. In the same time span, nine storms formed in December, two in April, and one each in January, February and March. During four years (1887, 1953, 2003, and 2007), tropical cyclones formed in the North Atlantic Ocean both during or before May and during December. In 1887, four storms occurred outside the season, the most in a single year. High vertical wind shear and low sea surface temperatures generally preclude tropical cyclone formation during the off-season.
Tropical cyclones have formed in all months.Four tropical cyclones existed during the month of January, two of which formed during late December: the second Hurricane Alice in 1954/1955, and Tropical Storm Zeta in 2005/2006. The only two hurricanes to form in January are a Category 1 hurricane in the 1938 season, and Hurricane Alex in the 2016 season. A subtropical storm in January also began the 1978 Atlantic hurricane season. No major hurricanes have occurred in the off-season.
While the number of storms in the Atlantic has increased since 1995, there is no obvious global trend. The annual number of tropical cyclones worldwide remains about 87 ± 10. However, the ability of climatologists to make long-term data analysis in certain basins is limited by the lack of reliable historical data in some basins, primarily in the Southern Hemisphere. In spite of that, there is some evidence that the intensity of hurricanes is increasing. In 2006, Kerry Emanuel stated, "Records of hurricane activity worldwide show an upswing of both the maximum wind speed in and the duration of hurricanes. The energy released by the average hurricane (again considering all hurricanes worldwide) seems to have increased by around 70% in the past 30 years or so, corresponding to about a 15% increase in the maximum wind speed and a 60% increase in storm lifetime." At the time, Emanuel theorized that increased heat from global warming was driving this trend, however, some argue that Emanuel's own research in 2008 refuted this theory. Others contend that the trend does not exist at all, but instead is a figment created by faulty readings from primitive 1970s-era measurement equipment.[ citation needed ] Vecchi and Knutson (2008) found a weakly positive, although not statistically-significant trend in the number of North Atlantic tropical cyclones for 1878–2006, but also a surprisingly strong decrease in cyclone duration over this period.
On May 15, 2014, the journal Nature published a peer-reviewed submission from October 2013 by James P. Kossin, Kerry A. Emanuel, and Gabriel A. Vecchi that suggests that a poleward migration exists for the paths of maximum intensity of tropical cyclone activity in the Atlantic. km per decade, amounting to approximately one degree of latitude per decade.The focus of the report is on the latitude at which recent tropical cyclones in the Atlantic are reaching maximum intensity. Their data indicates that during the past thirty years, the peak intensity of these storms has shifted poleward in both hemispheres at a rate of approximately 60
Atlantic storms are becoming more destructive financially, since five of the ten most expensive storms in United States history have occurred since 1990. According to the World Meteorological Organization, “recent increase in societal impact from tropical cyclones has largely been caused by rising concentrations of population and infrastructure in coastal regions.” billion of normalized damage.Pielke et al. (2008) normalized mainland U.S. hurricane damage from 1900–2005 to 2005 values and found no remaining trend of increasing absolute damage. The 1970s and 1980s were notable because of the extremely low amounts of damage compared to other decades. The decade 1996–2005 has the second most damage among the past 11 decades, with only the decade 1926–1935 surpassing its costs. The most damaging single storm is the 1926 Miami hurricane, with $157
Often in part because of the threat of hurricanes, many coastal regions had sparse population between major ports until the advent of automobile tourism; therefore, the most severe portions of hurricanes striking the coast may have gone unmeasured in some instances. The combined effects of ship destruction and remote landfall severely limit the number of intense hurricanes in the official record before the era of hurricane reconnaissance aircraft and satellite meteorology. Although the record shows a distinct increase in the number and strength of intense hurricanes, therefore, experts regard the early data as suspect.Christopher Landsea et al. estimated an undercount bias of zero to six tropical cyclones per year between 1851 and 1885 and zero to four per year between 1886 and 1910. These undercounts roughly take into account the typical size of tropical cyclones, the density of shipping tracks over the Atlantic basin, and the amount of populated coastline.
The number and strength of Atlantic hurricanes may undergo a 50–70 year cycle, also known as the Atlantic Multidecadal Oscillation. Nyberg et al. reconstructed Atlantic major hurricane activity back to the early eighteenth century and found five periods averaging 3–5 major hurricanes per year and lasting 40–60 years, and six other averaging 1.5–2.5 major hurricanes per year and lasting 10–20 years. These periods are associated with the Atlantic multidecadal oscillation. Throughout, a decadal oscillation related to solar irradiance was responsible for enhancing/dampening the number of major hurricanes by 1–2 per year.
Although more uncommon since 1995, few above-normal hurricane seasons occurred during 1970–94.Destructive hurricanes struck frequently from 1926–60, including many major New England hurricanes. Twenty-one Atlantic tropical storms formed in 1933, a record only recently exceeded in 2005, which saw 28 storms. Tropical hurricanes occurred infrequently during the seasons of 1900–25; however, many intense storms formed during 1870–99. During the 1887 season, 19 tropical storms formed, of which a record 4 occurred after November 1 and 11 strengthened into hurricanes. Few hurricanes occurred in the 1840s to 1860s; however, many struck in the early 19th century, including an 1821 storm that made a direct hit on New York City. Some historical weather experts say these storms may have been as high as Category 4 in strength.
These active hurricane seasons predated satellite coverage of the Atlantic basin. Before the satellite era began in 1960, tropical storms or hurricanes went undetected unless a reconnaissance aircraft encountered one, a ship reported a voyage through the storm, or a storm landed in a populated area.The official record, therefore, could miss storms in which no ship experienced gale-force winds, recognized it as a tropical storm (as opposed to a high-latitude extra-tropical cyclone, a tropical wave, or a brief squall), returned to port, and reported the experience.
Proxy records based on paleotempestological research have revealed that major hurricane activity along the Gulf of Mexico coast varies on timescales of centuries to millennia.Few major hurricanes struck the Gulf coast during 3000–1400 BC and again during the most recent millennium. These quiescent intervals were separated by a hyperactive period during 1400 BC and 1000 AD, when the Gulf coast was struck frequently by catastrophic hurricanes and their landfall probabilities increased by 3–5 times. This millennial-scale variability has been attributed to long-term shifts in the position of the Azores High, which may also be linked to changes in the strength of the North Atlantic Oscillation.
According to the Azores High hypothesis, an anti-phase pattern is expected to exist between the Gulf of Mexico coast and the Atlantic coast. During the quiescent periods, a more northeasterly position of the Azores High would result in more hurricanes being steered towards the Atlantic coast. During the hyperactive period, more hurricanes were steered towards the Gulf coast as the Azores High was shifted to a more southwesterly position near the Caribbean. Such a displacement of the Azores High is consistent with paleoclimatic evidence that shows an abrupt onset of a drier climate in Haiti around 3200 14C years BP, years, just as the Gulf Coast was amid a quiescent period during the last millennium. Evidence also shows that the average latitude of hurricane impacts has been steadily shifting northward, towards the Eastern Seaboard over the past few centuries. This change has been sped up in modern times due to the Arctic Ocean heating up especially much from fossil fuel-caused global warming.and a change towards more humid conditions in the Great Plains during the late-Holocene as more moisture was pumped up the Mississippi Valley through the Gulf coast. Preliminary data from the northern Atlantic coast seem to support the Azores High hypothesis. A 3,000-year proxy record from a coastal lake in Cape Cod suggests that hurricane activity increased significantly during the past 500–1000
The 2002 Atlantic hurricane season was a borderline-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; the 2002 season tied with 2010 in which a record number of tropical storms, eight, 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. The season's low activity is reflected in the low cumulative accumulated cyclone energy (ACE) rating of 67. ACE is, broadly speaking, a measure of the power of the hurricane multiplied by the length of time it existed, so low number reflects the small number of strong storms and preponderance of tropical storms.
The 1979 Atlantic hurricane season was the first season to include both male and female names, as well as the common six-year rotating lists of tropical cyclone names. 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. It was slightly below average, with nine systems reaching tropical storm intensity. The first system, an unnumbered tropical depression, developed north of Puerto Rico on June 9. Two days later, Tropical Depression One formed and produced severe flooding in Jamaica, with 40 deaths and about $27 million (1979 USD) in damage. Tropical Storm Ana caused minimal impact in the Lesser Antilles. Hurricane Bob spawned tornadoes and produced minor wind damage along the Gulf Coast of the United States, primarily in Louisiana, while the remnants caused flooding, especially in Indiana. Tropical Storm Claudette caused extensive flooding, due to torrential rainfall. There were two deaths and damaged totaled $750 million.
The 1957 Atlantic hurricane season featured the one of longest travelling tropical cyclones in the Atlantic basin, Hurricane Carrie. Nevertheless, the season was generally inactive with eight tropical storms – two of which went unnamed – and three hurricanes, two of which intensified further to attain major hurricane intensity. The season officially began on June 15 and ended on November 15, though the year's first tropical cyclone developed prior to the start of the season on June 8. The final storm dissipated on October 27, well before the official end of the season. The strongest hurricane of the year was Carrie, which reached the equivalent of a Category 4 hurricane on the Saffir–Simpson hurricane scale on two separate occasions in the open Atlantic; Carrie later caused the sinking of the German ship Pamir southwest of the Azores, resulting in 80 deaths.
The 2005 Atlantic hurricane season was the most active Atlantic hurricane season in recorded history, shattering numerous records. The impact of the season was widespread and catastrophic. Its storms caused an estimated total of 3,960 deaths and approximately $180.7 billion in damage, making it the second costliest season on record, surpassed only by the 2017 season.
The 2006 Atlantic hurricane season was the least active since 1997 as well as the first season since 2001 in which no hurricanes made landfall in the United States, and was the first since 1994 in which no tropical cyclones formed during October. Following the intense activity of 2005, forecasters predicted that the 2006 season would be only slightly less active. Instead activity was slowed by a rapidly forming moderate El Niño event, the presence of the Saharan Air Layer over the tropical Atlantic, and the steady presence of a robust secondary high-pressure area to the Azores high centered on Bermuda. There were no tropical cyclones after October 2.
The 1938 Atlantic hurricane season began earlier than any Atlantic hurricane season on record lasting from January 3 through October 31. The season was generally quiet with 9 tropical cyclones and 4 becoming hurricane strength, 2 of which became major hurricane equivalent.
The 1935 Atlantic hurricane season ran from June 1 through November 30, 1935. The 1935 season featured below average activity, but it was eventful. A Category 1 hurricane in the Caribbean killed an estimated 2,150 people in the Greater Antilles and Central America. A Category 3 storm hit central Cuba and grazed Miami. An extratropical hurricane hit Newfoundland. The third tropical cyclone of the season struck the Florida Keys in southern Florida as a Category 5 hurricane; it remains the strongest landfalling hurricane in the United States or anywhere in the Atlantic basin, tied with Dorian of 2019. A rare November hurricane also affected the Miami—Fort Lauderdale area.
The 1920 Atlantic hurricane season featured tropical storms and hurricanes only in the month of September. Although no "hurricane season" was defined at the time, the present-day delineation of such is June 1 to November 30. The first system, a hurricane, developed on September 7 while the last, a tropical depression, transitioned into an extratropical cyclone on October 27. Of note, four of the six cyclones co-existed with another tropical cyclone during the season.
The 1913 Atlantic hurricane season was the third consecutive year with a tropical cyclone developing before June. Although no "hurricane season" was defined at the time, the present-day delineation of such is June 1 to November 30. 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 Atlantic hurricane season is the period in a year when hurricanes usually form in the Atlantic Ocean. Tropical cyclones in the North Atlantic are called hurricanes, tropical storms, or tropical depressions. In addition, there have been several storms over the years that have not been fully tropical and are categorized as subtropical depressions and subtropical storms. Even though subtropical storms and subtropical depressions are not technically as strong as tropical cyclones, the damages can still be devastating.
The 1886 Atlantic hurricane season ran through the early summer and the first half of fall in 1886. This is the period of each year when most tropical cyclones form in the Atlantic basin. It was a very active year, with ten hurricanes, seven of which struck the United States. Four hurricanes became major hurricanes. However, in the absence of modern satellite and other remote-sensing technologies, only storms that affected populated land areas or encountered ships at sea are known, so the actual total could be higher. An undercount bias of zero to six tropical cyclones per year between 1851 and 1885 and zero to four per year between 1886 and 1910 has been estimated. Of the known 1886 cyclones, Hurricane Seven and Tropical Storm Eleven were first documented in 1996 by Jose Fernandez-Partagas and Henry Diaz. They also proposed large alterations to the known tracks of several other 1886 storms.
Traditionally, areas of tropical cyclone formation are divided into seven basins. These include the north Atlantic Ocean, the eastern and western parts of the northern Pacific Ocean, the southwestern Pacific, the southwestern and southeastern Indian Oceans, and the northern Indian Ocean. The western Pacific is the most active and the north Indian the least active. An average of 86 tropical cyclones of tropical storm intensity form annually worldwide, with 47 reaching hurricane/typhoon strength, and 20 becoming intense tropical cyclones, super typhoons, or major hurricanes.
The 2019 Atlantic hurricane season is an ongoing event in the annual formation of tropical cyclones in the Northern Hemisphere. The season officially began on June 1, 2019, and will end on November 30, 2019. 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, marking the record fifth year in a row where a tropical or subtropical cyclone developed before the official start of the season, breaking the previous record of four years set in 1951–1954. This was also the second year in a row in which no storms formed during the month of June.