The Gulf Stream influences the climate of the east coast of North America from Florida to Newfoundland, and the west coast of Europe. Although there has been recent debate, there is consensus that the climate of Western Europe and Northern Europe is warmer than other areas of similar latitude because of the North Atlantic Current. It is part of the North Atlantic Gyre. Its presence has led to the development of strong cyclones of all types, both within the atmosphere and within the ocean. The Gulf Stream is also a significant potential source of renewable power generation.
Introduction
Gulf Stream
Gulf Stream | Introduction
Its presence has led to the development of strong cyclones of all types, both within the atmosphere and within the ocean. Yes - the warm water and temperature contrast along the edge of the Gulf Stream often increase the intensity of cyclones Yes, Tropical cyclones Yes.
what does gulf stream refer to?
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It is a warm and swift Atlantic ocean current
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where does it originate?
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It originates in the Gulf of Mexico and stretches to the tip of Florida, and follows the eastern coastlines of the United States and Newfoundland before crossing the Atlantic Ocean as the North Atlantic Current.
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does it help a cyclone to form?
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The warm water and temperature contrast along the edge of the Gulf Stream often increase the intensity of cyclones, tropical or otherwise. Tropical cyclone generation normally requires water temperatures in excess of . Tropical cyclone formation is common over the Gulf Stream, especially in the month of July. Storms travel westwards through the Caribbean and then either move in a northwards direction and curve towards the eastern coast of the United States or stay on a north-westwards track and enter the Gulf of Mexico. Such storms have the potential to create strong winds and extensive damage to the United States' Southeast Coastal Areas.
Gulf Stream | Effect on cyclone formation
Hurricane Sandy in 2012 was a recent example of a hurricane passing over the Gulf Stream and gaining strength. Strong extratropical cyclones have been shown to deepen significantly along a shallow frontal zone, forced by the Gulf Stream, during the cold season. Subtropical cyclones also tend to generate near the Gulf Stream. 75 percent of such systems documented between 1951 and 2000 formed near this warm water current, with two annual peaks of activity occurring during the months of May and October. Cyclones within the ocean form under the Gulf Stream, extending as deep as beneath the ocean's surface.
Gulf Stream | Effect on cyclone formation
Nor'easters develop in response to the sharp contrast in the warm Gulf Stream ocean current coming up from the tropical Atlantic and the cold air masses coming down from Canada. When the very cold and dry air rushes southward and meets up with the warm Gulf stream current, which is often near even in mid-winter, intense low pressure develops. In the upper atmosphere, the strong winds of the jet stream remove and replace rising air from the Atlantic more rapidly than the Atlantic air is replaced at lower levels; this and the Coriolis force help develop a strong storm. The storm tracks northeast along the East Coast, normally from North Carolina to Long Island, then moves toward the area east of Cape Cod.
Nor'easter | Formation
Tropical cyclones typically form from large, disorganized areas of disturbed weather in tropical regions. As more thunderstorms form and gather, the storm develops rainbands which start rotating around a common center. As the storm gains strength, a ring of stronger convection forms at a certain distance from the rotational center of the developing storm. Since stronger thunderstorms and heavier rain mark areas of stronger updrafts, the barometric pressure at the surface begins to drop, and air begins to build up in the upper levels of the cyclone. This results in the formation of an upper level anticyclone, or an area of high atmospheric pressure above the central dense overcast.
Eye (cyclone) | Formation and detection
Climatology serves 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. 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 .
Atlantic hurricane | Climatology
Consequently, most of this built up air flows outward anticyclonically above the tropical cyclone. Outside the forming eye, the anticyclone at the upper levels of the atmosphere enhances the flow towards the center of the cyclone, pushing air towards the eyewall and causing a positive feedback loop. However, a small portion of the built-up air, instead of flowing outward, flows inward towards the center of the storm. This causes air pressure to build even further, to the point where the weight of the air counteracts the strength of the updrafts in the center of the storm. Air begins to descend in the center of the storm, creating a mostly rain-free area—a newly formed eye.
Eye (cyclone) | Formation and detection
Most tropical cyclones form in a worldwide band of thunderstorm activity near the equator, referred to as the Intertropical Front (ITF), the Intertropical Convergence Zone (ITCZ), or the monsoon trough. Another important source of atmospheric instability is found in tropical waves, which contribute to the development of about 85% of intense tropical cyclones in the Atlantic Ocean and become most of the tropical cyclones in the Eastern Pacific. The majority forms between 10 and 30 degrees of latitude away of the equator, and 87% forms no farther away than 20 degrees north or south. Because the Coriolis effect initiates and maintains their rotation, tropical cyclones rarely form or move within 5 degrees of the equator, where the effect is weakest.
Tropical cyclone | Locations
Strong cold fronts typically feature narrow bands of thunderstorms and severe weather, and may on occasion be preceded by squall lines or dry lines. Such fronts form west of the circulation center and generally move from west to east; warm fronts form east of the cyclone center and are usually preceded by stratiform precipitation and fog. Warm fronts move poleward ahead of the cyclone path. Occluded fronts form late in the cyclone life cycle near the center of the cyclone and often wrap around the storm center. Tropical cyclogenesis describes the process of development of tropical cyclones. Tropical cyclones form due to latent heat driven by significant thunderstorm activity, and are warm core.
Cyclone | Introduction
This region includes the North Atlantic Ocean, the Caribbean Sea, and the Gulf of Mexico. Tropical cyclone formation here varies widely from year to year, ranging from one to over twenty-five per year. Most Atlantic tropical storms and hurricanes form between June 1 and November 30. The United States National Hurricane Center (NHC) monitors the basin and issues reports, watches and warnings about tropical weather systems for the Atlantic Basin as one of the Regional Specialized Meteorological Centres for tropical cyclones as defined by the World Meteorological Organization. On average, 11 named storms (of tropical storm or higher strength) occur each season, with an average of 6 becoming hurricanes and 2 becoming major hurricanes.
Tropical cyclone basins | North Atlantic Ocean
Low amounts of wind shear are needed, as high shear is disruptive to the storm's circulation. Lastly, a formative tropical cyclone needs a pre-existing system of disturbed weather, although without a circulation no cyclonic development will take place. Mesocyclones form as warm core cyclones over land, and can lead to tornado formation. Waterspouts can also form from mesocyclones, but more often develop from environments of high instability and low vertical wind shear. In deserts, lack of ground and plant moisture that would normally provide evaporative cooling can lead to intense, rapid solar heating of the lower layers of air. The hot air is less dense than surrounding cooler air.
Low-pressure area | Formation
The origins of Fay were from a mesocyclonic vortex (MCV) over the deep south. The MCV merged with a trough that extended from the Gulf of Mexico to the western Atlantic Ocean. Late on July 4, the National Hurricane Center (NHC) first mentioned the possibility of eventual tropical cyclone formation from the trough in the northern Gulf of Mexico, which at that time consisted of disorganized convection, or thunderstorms. A day later, a low pressure area formed near the northern Gulf Coast, which soon moved ashore the Florida panhandle. The low moved into Georgia on July 6, and into South Carolina two days later, accompanied by a large area of thunderstorms over the southeastern United States.
Tropical Storm Fay (2020) | Meteorological history
Since they form from extratropical cyclones, which have colder temperatures aloft than normally found in the tropics, the sea surface temperatures required is around 23 degrees Celsius (73 °F) for their formation, which is three degrees Celsius (5 °F) lower than for tropical cyclones. This means that subtropical cyclones are more likely to form outside the traditional bounds of the hurricane season. Although subtropical storms rarely have hurricane-force winds, they may become tropical in nature as their cores warm.
Cyclone | Subtropical
Tropical cyclones form due to latent heat driven by significant thunderstorm activity, and are warm-core with well-defined circulations. Certain criteria need to be met for their formation. In most situations, water temperatures of at least are needed down to a depth of at least ; waters of this temperature cause the overlying atmosphere to be unstable enough to sustain convection and thunderstorms. Another factor is rapid cooling with height, which allows the release of the heat of condensation that powers a tropical cyclone. High humidity is needed, especially in the lower-to-mid troposphere; when there is a great deal of moisture in the atmosphere, conditions are more favorable for disturbances to develop.
Low-pressure area | Formation
A tropical wave emerged into the Atlantic Ocean off the west coast of Africa during the last week of July. As it tracked across the Atlantic, it remained a well-defined system, but never organized into a tropical cyclone. On August 8, the system entered the Gulf of Mexico, and by the following day, it developed a weak low-level circulation. The circulation became better defined later that day, and was confirmed by Reconnaissance aircraft that afternoon, when it was declared Tropical Depression Eight while east of Tamaulipas. From the outset, the cyclone's motion was altered by Hurricane Flossie off the Pacific coast of Mexico.
Tropical Storm Gabrielle (1995) | Meteorological history
Cyclones can transition between extratropical, subtropical, and tropical phases. Mesocyclones form as warm core cyclones over land, and can lead to tornado formation. Waterspouts can also form from mesocyclones, but more often develop from environments of high instability and low vertical wind shear. In the Atlantic and the northeastern Pacific oceans, a tropical cyclone is generally referred to as a hurricane (from the name of the ancient Central American deity of wind, Huracan), in the Indian and south Pacific oceans it is called a cyclone, and in the northwestern Pacific it is called a typhoon. The growth of instability in the vortices is not universal.
Cyclone | Introduction
A weak and broad frontal low absorbed the remnants of Tropical Depression Ten in the central Gulf of Mexico. The Hydrometeorological Prediction Center identified the system as a subtropical storm on October 1. The subtropical storm moved across Florida and the Southeastern United States on October 2 and 3; when it reached the Atlantic Coast, it became an extratropical frontal wave. However, the National Hurricane Center does not confirm the existence of the subtropical cyclone. In addition to the seven named storms, a nor'easter formed in late December. As it entered the warm waters of the Gulf Stream in the Atlantic Ocean, it began to rapidly intensify, exhibiting signs of tropical development, including the formation of an eye.
1994 Atlantic hurricane season | Other systems
A preexisting frontal boundary, as defined in surface weather analysis, is required for the development of a mid-latitude cyclone. The cyclonic flow begins around a disturbed section of the stationary front due to an upper level disturbance, such as a short wave or an upper-level trough, near a favorable quadrant of the upper level jet. However, enhanced along-frontal stretching rates in the lower troposphere can suppress the growth of extratropical cyclones.
Cyclogenesis | Precursors for development
A non-tropical trough at the surface extended from the northern Gulf of Mexico across Florida into the western Atlantic Ocean. On August 3, the western portion developed into a low pressure area. The eastern portion slowly organized and ultimately developed into Tropical Storm Cristobal. The low pressure area in the Gulf of Mexico steadily organized, and late on August 4 the circulation was organized enough for the National Hurricane Center to classify it as Tropical Depression Two while located 40 miles (65 km) east of Port Eads, Louisiana. Northeasterly wind shear initially prevented organization of the cloud pattern, though the depression was able to strengthen to become Tropical Storm Bertha about five hours after it formed.
Tropical Storm Bertha (2002) | Meteorological history
Collectively, these factors worked to suppress tropical cyclogenesis. Tropical cyclogenesis began in early June, with the development of Tropical Storm Andrea in the Gulf of Mexico on June 5. Twelve days later, Tropical Storm Barry formed in the northwestward Caribbean Sea. Two named storms originated in the month of July—tropical storms Chantal and Dorian. Similarly, there were two tropical storms in August, Erin and Fernand. In September, four tropical cyclones formed, three of which strengthened into tropical storms; two of those reached hurricane status. The most intense tropical cyclone—Hurricane Humberto—peaked with maximum sustained winds of on September 11, which is a Category 1 on the Saffir–Simpson hurricane wind scale.
2013 Atlantic hurricane season | Seasonal summary
Due to the initial cold temperatures aloft, sea surface temperatures usually need to reach at least for this initial round of thunderstorms. The initial thunderstorm activity moistens up the environment around the low, which destabilizes the atmosphere by reducing the lapse rate needed for convection. When the next shortwave or upper level jet streak (wind maximum within the jet stream) moves nearby, convection reignites closer to the center and the system develops into a true subtropical cyclone. The average sea surface temperature that helps lead to subtropical cyclogenesis is . If the thunderstorm activity becomes deep and persistent, allowing its initial low level warm core to deepen, tropical cyclogenesis is possible.
Subtropical cyclone | Formation
This also means that subtropical cyclones are more likely to form outside the traditional bounds of the North Atlantic hurricane season. Subtropical cyclones are also observed to form in the South Atlantic; South Atlantic subtropical cyclones are observed in all months.
Subtropical cyclone | Introduction
A broad mid-tropospheric trough over the southeastern United States spawned an area of convection over the lower Mississippi River Valley on July 13, and drifted southward towards the warm waters of the Gulf of Mexico. As it moved into the Gulf of Mexico, a weak and isolated surface low pressure area formed off the coast of Louisiana. The circulation in the system steadily expanded, and initially the surface winds and convection were intermittent. On July 16, deep convection increased and organized near the center, and oil rigs and surface buoys reported surface winds of 30 mph (50 km/h). Based on the observations, it is estimated the system developed into Tropical Depression Four on July 16 while about 150 miles (240 km) south of the southwestern Louisiana coastline.
Hurricane Danny (1997) | Meteorological history
In the case of the north Indian Ocean, the formation of this type of vortex leads to the onset of monsoon rains during the wet season. In the southern hemisphere, subtropical cyclones are regularly observed across southern portions of the Mozambique Channel. Most subtropical cyclones form when a deep cold-core extratropical cyclone drops down into the subtropics. The system becomes blocked by a high latitude ridge, and eventually sheds its frontal boundaries as its source of cool and dry air from the high latitudes diverts away from the system. Temperature differences between the 500 hPa pressure level and the sea surface temperatures initially exceed the dry adiabatic lapse rate, which causes an initial round of thunderstorms to form at a distance east of the center.
Subtropical cyclone | Formation
By that time, the track and intensity of the new storm were not clear. Likewise it was unclear if the new weather feature would affect Europe as a cyclone or if it would remain an open trough until it arrives. By 16 January the trough now stretched from its Southern Caribbean origin to eastern Newfoundland. During that day, the trough developed a circulation centre near its northern end (Newfoundland), forming closed isobars around it which indicate a closed wind circulation and qualify the system as an extratropical cyclone. Hours after formation, the storm was caught by Fionn's strong jetstream and started moving to the east, posing a threat to Europe.
Storm David | Meteorological history
Tropical cyclones do not typically bring high winds to the southwestern United States. Most Pacific hurricanes are embedded in easterly winds south of the subtropical ridge, and thus move westward—away from large land masses—until they dissipate over cold waters. However, during early autumn, tropical cyclones generally form closer to the Mexican shoreline than average, making them more likely to recurve, or to curve again, northwards under the influence of an approaching trough. These troughs tend to extend farther to the south during the latter part of the Pacific hurricane season, in the period between late August and early October. They also produce a synoptic-scale flow that is conducive to steering hurricanes towards the southwestern United States.
Hurricane Kathleen (1976) | Background
A broad trough developed over the eastern Gulf of Mexico on May 26. A frontal disturbance formed over Florida along the trough, spawning an area of broad cyclonic turning. After emerging into the western Atlantic Ocean, a closed circulation developed within the system, and it is estimated that a tropical depression formed on May 28 about 100 mi (160 km) east of Jacksonville, Florida. Ship observations in the region suggested that the depression intensified into a tropical storm by late on May 28. The system was small, and was not discovered to have been a tropical cyclone until a reanalysis of data in 2015.
1954 Atlantic hurricane season | Tropical Storm One
At the end of May 2013, a broad and diffuse cyclonic disturbance developed over eastern Mexico and northern Central America, incorporating the remnants of eastern Pacific Hurricane Barbara. As a tropical wave approached from the east, an inverted trough developed on the northern edge of the active region on June 2, setting the stage for the formation of a weak surface low pressure system over the southern Gulf of Mexico the next day. The National Hurricane Center (NHC) began monitoring the system in their Tropical Weather Outlooks, and bulletins were issued every six hours regarding the probability of tropical cyclone formation within 48 hours.
Tropical Storm Andrea (2013) | Meteorological history
A river of sea water, called the Atlantic North Equatorial Current, flows westwards off the coast of Central Africa. When this current interacts with the northeastern coast of South America, the current forks into two branches. One passes into the Caribbean Sea, while a second, the Antilles Current, flows north and east of the West Indies. These two branches rejoin north of the Straits of Florida. The trade winds blow westwards in the tropics, and the westerlies blow eastwards at mid-latitudes. This wind pattern applies a stress to the subtropical ocean surface with negative curl across the north Atlantic Ocean.
Gulf Stream | Formation and behaviour
Squall lines, or solid bands of strong thunderstorms, can form ahead of cold fronts and lee troughs due to the presence of significant atmospheric moisture and strong upper level divergence, leading to hail and high winds. When significant directional wind shear exists in the atmosphere ahead of a cold front in the presence of a strong upper-level jet stream, tornado formation is possible. Although tornadoes can form anywhere on Earth, the greatest number occur in the Great Plains in the United States, because downsloped winds off the north–south oriented Rocky Mountains, which can form a dryline, aid their development at any strength.
Extratropical cyclone | Severe weather
On July 29, 1987, a tropical wave emerged off the west coast of Africa into the Atlantic Ocean. Tracking westward along the southern edge of the Saharan Air Layer, a feature associated with large masses of dry air, little convective development took place over the following several days. Once near the Lesser Antilles in early August, atmospheric conditions became more favorable for development. Traveling across the Caribbean Sea, the system became increasingly organized and a mid-level circulation formed shortly before the wave moved inland over Central America on August 7. The following day, the northern portion of the wave interacted with a cold-core low over the Gulf of Mexico, resulting in the formation of a low-level circulation, exhibiting tropical characteristics, on August 9.
1987 Gulf Coast tropical storm | Meteorological history
At 00:00 UTC July 5, shortly after the formation of Tropical Storm Edouard, the NHC began to track an area of disorganized cloudiness and showers in relation to a nearly stationary surface trough in the Gulf of Mexico. After meandering over the Gulf, the disturbance moved northeast towards the coast of the Florida Panhandle, and would subsequently move inland by 12:00 UTC July 6. Two days later, the system re-emerged over the coast of Georgia. Once offshore, the system began to organize as deep convection blossomed over the warm waters of the Gulf Stream. Three hours later, the center reformed near the edge of the primary convective mass, prompting the NHC to initiate advisories on Tropical Storm Fay at 21:00 UTC July 9, located just 40 miles east-northeast of Cape Hatteras.
2020 Atlantic hurricane season | Tropical Storm Fay
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.
Atlantic hurricane | July
Water temperatures in the Arabian Sea are typically warm enough to allow for tropical cyclogenesis year round, although strong wind shear from the monsoon trough prevents formation in the summer months and limits intensity other times of the year. An increase in air pollution since the 1930s caused a decrease in the wind shear, allowing storms to have become stronger since 1979.
North Indian Ocean tropical cyclone | History of the basin
While an initial warm core system, such as an organized thunderstorm complex, is necessary for the formation of a tropical cyclone, a large flux of energy is needed to lower atmospheric pressure more than a few millibars (0.10 inch of mercury). Inflow of warmth and moisture from the underlying ocean surface is critical for tropical cyclone strengthening. A significant amount of the inflow in the cyclone is in the lowest of the atmosphere.
Inflow (meteorology) | Tropical cyclones
Subtropical cyclones form in a wide band of latitude, mainly south of the 50th parallel in the northern hemisphere. Due to the increased frequency of cyclones which cut off from the main belt of the westerlies during the summer and fall, subtropical cyclones are significantly more frequent across the North Atlantic than the northwestern Pacific Ocean. In the eastern half of the north Pacific Ocean and north Indian Ocean, the older subtropical cyclone definition term is still used, which requires a weak circulation forming underneath a mid to upper-tropospheric low which has cut off from the main belt of the westerlies during the cold season (winter).
Subtropical cyclone | Formation
Extratropical cyclones form along linear bands of temperature/dewpoint gradient with significant vertical wind shear, and are thus classified as baroclinic cyclones. Initially, cyclogenesis, or low pressure formation, occurs along frontal zones near a favorable quadrant of a maximum in the upper level jetstream known as a jet streak. The favorable quadrants are usually at the right rear and left front quadrants, where divergence ensues. The divergence causes air to rush out from the top of the air column. As mass in the column is reduced, atmospheric pressure at surface level (the weight of the air column) is reduced. The lowered pressure strengthens the cyclone (a low pressure system).
Extratropical cyclone | Cyclogenesis
A broad surface trough extended from the western Atlantic Ocean into the Gulf of Mexico in early September 2002. At the same time, a westward-moving tropical wave entered the gulf on September 10 and spawned a weak low along the trough, with little associated thunderstorm activity. On September 11, an upper-level low over the United States moved into the Gulf and became cut off from the flow, allowing atmospheric convection to develop to the east of the tropical wave. The surface low organized, and convection formed closer to the center of the low. At 0000 UTC on September 12, a Hurricane Hunters aircraft was able to find a well-defined center of circulation; the National Hurricane Center (NHC) thus designated it a tropical depression while it was about south of Pensacola, Florida.
Tropical Storm Hanna (2002) | Meteorological history
The Gulf Stream, together with its northern extension towards Europe, the North Atlantic Drift, is a powerful, warm, and swift Atlantic ocean current that originates at the tip of Florida, and follows the eastern coastlines of the United States and Newfoundland before crossing the Atlantic Ocean. The process of western intensification causes the Gulf Stream to be a northward accelerating current off the east coast of North America. At about , it splits in two, with the northern stream crossing to northern Europe and the southern stream recirculating off West Africa. The Gulf Stream influences the climate of the east coast of North America from Florida to Newfoundland, and the west coast of Europe.
Thermohaline circulation | Gulf Stream
Hurricane-force extratropical cyclones are most likely to form in the northern Atlantic and northern Pacific oceans in the months of December and January. On 14 and 15 December 1986, an extratropical cyclone near Iceland deepened to below , which is a pressure equivalent to a category 5 hurricane. In the Arctic, the average pressure for cyclones is during the winter, and during the summer.
Extratropical cyclone | Cyclogenesis
Tropical cyclones are typically between in diameter. The strong rotating winds of a tropical cyclone are a result of the conservation of angular momentum imparted by the Earth's rotation as air flows inwards toward the axis of rotation. As a result, they rarely form within 5° of the equator. Tropical cyclones are almost unknown in the South Atlantic due to a consistently strong wind shear and a weak Intertropical Convergence Zone. Conversely, the African easterly jet and areas of atmospheric instability give rise to cyclones in the Atlantic Ocean and Caribbean Sea, while cyclones near Australia owe their genesis to the Asian monsoon and Western Pacific Warm Pool.
Tropical cyclone | Introduction
A wave along a frontal boundary, in the form of a broad area of low pressure, develops as an upper level disturbance moves towards that portion of the boundary. Precipitation will begin to form ahead of the surface low, within the cold sector of the cyclone poleward of the warm front. As the low deepens, both the cold and warm fronts around the low become better defined. As the low matures, it couples with the upper level disturbance moving into the cyclone's cold sector. The cold front catches up to the westward portion of the warm front, forming an occluded front.
Norwegian cyclone model | Evolution
Tini/Darwin formed over the eastern USA on 10 February, before undergoing Explosive cyclogenesis as it moved across the Atlantic under the influence of a strong Jet stream during 11 February which stretched from the eastern USA to Central Europe. The storm developed as it moved eastward over the North Atlantic reaching a low pressure nadir of to the west of Slyne Head county Galway. The storm developed according to the Shapiro-Keyser model, displaying frontal fracture. The storm developed a Sting jet. Tini brought hurricane-force winds to areas of Ireland, Wales and England, and brought some high rainfall totals over the UK and Ireland.
Cyclone Tini | Meteorological history
The precursor system that would form Dean was a stationary front situated in the northeastern Gulf of Mexico in the last week of July. On July 27, it developed a weak upper-level circulation indicated by reports from buoys in the Gulf, its structure was disorganized but was in the process of organizing. The system continued to organize early on July 28, and that afternoon it developed a surface circulation. The tropical depression that spawned Dean was thought to have formed at around 1800 UTC, July 28. It was later declared Tropical Depression Four that same day with the center located about 345 miles (555 km) southeast of New Orleans.
Tropical Storm Dean (1995) | Meteorological history
Hurricane Karl originated in a low pressure area that formed along a frontal boundary near the southeastern United States. It approached the Canadian Maritimes the next day and strengthened to below 1000 millibars. On November 24, the broad cyclone was located south of Newfoundland, and early the next day a mass of convection developed near the core. It evolved into a separate vortex, and due to the lack of inhibiting wind shear, a small cyclone developed. It became a subtropical storm at 00:00 UTC before executing a tight counterclockwise loop as it rotated within the larger cyclone. About 18 hours later, the storm strengthened and gained enough tropical characteristics to be designated a hurricane, accompanied by the formation of a pronounced eye feature.
Hurricane Karl (1980) | Meteorological history
Cyclogenesis is the development or strengthening of cyclonic circulation in the atmosphere. Cyclogenesis is an umbrella term for several different processes that all result in the development of some sort of cyclone. It can occur at various scales, from the microscale to the synoptic scale. Extratropical cyclones begin as waves along weather fronts before occluding later in their life cycle as cold-core systems. However, some intense extratropical cyclones can become warm-core systems when a warm seclusion occurs. Tropical cyclones form as a result of significant convective activity, and are warm core. Mesocyclones form as warm core cyclones over land, and can lead to tornado formation.
Cyclone | Formation
There are six main requirements for tropical cyclogenesis: sufficiently warm sea surface temperatures, atmospheric instability, high humidity in the lower to middle levels of the troposphere, enough Coriolis force to sustain a low pressure center, a preexisting low level focus or disturbance, and low vertical wind shear. While these conditions are necessary for tropical cyclone formation, they do not guarantee that a tropical cyclone will form.
Tropical cyclogenesis | Requirements for tropical cyclone formation
Usually, an anticyclone in the upper layers of the troposphere above the storm must be present as well—for extremely low surface pressures to develop, air must be rising very rapidly in the eyewall of the storm, and an upper-level anticyclone helps channel this air away from the cyclone efficiently.
Tropical cyclone | Rapid intensification
By July 8, the NHC assessed a high probability of a tropical cyclone developing due to favorable conditions in the Gulf. On July 9, a broad low pressure area exited the Florida Panhandle and tracked into the northeastern Gulf of Mexico, accompanied by scattered convection, or thunderstorms. It moved southwestward and curved to the west on the east side of a mid-level ridge. On July 10, the NHC initiated advisories on the system as "Potential Tropical Cyclone Two", due to its threat it posed to the United States within a few days. At that time, the low pressure area was experiencing some northerly wind shear, which was expected to decrease.
Hurricane Barry (2019) | Meteorological history
In late August 2011, much of the western Caribbean came under the influence of abundant tropical moisture. Combined with favorable upper diffluence, the moisture allowed for a perpetual area of disturbed weather to form; this, in return, contributed to the genesis of a weak tropical wave, or an elongated low-pressure feature at the lower levels of the atmosphere. The wave initiated a more-or-less westward, then west-northwestward drift across the Yucatán Peninsula toward the Gulf of Mexico, although it remained largely disorganized while doing so. After arriving in the gulf on August 31, the system failed to develop much under initially high wind shear; however, the National Hurricane Center forecast some potential for the formation of a tropical cyclone in a day or two.
Tropical Storm Lee (2011) | Meteorological history
Across the eastern half of the northern Pacific, they require a mid-tropospheric cyclone to be cut off from the main belt of the westerlies and only a weak surface circulation. Subtropical cyclones have broad wind patterns with maximum sustained winds located farther from the center than typical tropical cyclones, and have no weather fronts linked into their center. Since they form from initially extratropical cyclones which have colder temperatures aloft than normally found in the tropics, the sea surface temperatures required for their formation are lower than the tropical cyclone threshold by 3°C (5°F), lying around 23 °C (73 °F).
Subtropical cyclone | Introduction
The origin of Hurricane Alicia can be traced to a frontal boundary that extended from New England to the Gulf of Mexico. This weak front was initially stationary over the Southeastern United States but moved slowly southward into the north-central and northeastern fringes of the gulf, producing strong convective activity beginning on the night of August 13, 1983. On August 14, a small area of low pressure developed on the western end of the front and moved off the coasts of Mississippi and Alabama, intensifying as it progressed further into the open gulf waters. The thunderstorms associated with the small low-pressure area—described as a mesoscale convective complex—aided in the development of additional storms in the northern Gulf of Mexico by facilitating favorable conditions for convective initiation.
Hurricane Alicia | Meteorological history
It was initially thought that tropical cyclones did not develop within the South Atlantic. Very strong vertical wind shear in the troposphere is considered a deterrent. The Intertropical Convergence Zone drops one to two degrees south of the equator, not far enough from the equator for the Coriolis force to significantly aid development. Water temperatures in the tropics of the southern Atlantic are cooler than those in the tropical north Atlantic. During April 1991, these assertions were proven false, when the United States' National Hurricane Center (NHC) reported that a tropical cyclone had developed over the Eastern South Atlantic. In subsequent years, a few systems were suspected to have the characteristics needed to be classified as a tropical cyclone, including in March 1994 and January 2004.
South Atlantic tropical cyclone | Theories concerning infrequency of occurrence
Canada was affected by several tropical cyclones during 2006, including Alberto, the unnamed storm, Beryl, Florence, and Isaac. On June 20, an upper-level disturbance formed east of the Bahamas and moved westward across the islands. Between June 24 and 26, areas of convection developed occasionally, and a low-level disturbance formed. The system turned northward and upon reaching the Gulf Stream on June 27, it began to mature. It made landfall near Morehead City, North Carolina and moved northeastward along the U.S. East Coast. The storm contributed to severe and deadly flooding in the Mid-Atlantic States. While the NHC did not operationally classify it, data from reconnaissance aircraft, NEXRAD weather radar, and surface observations suggest it may have met the criteria for a tropical cyclone.
2006 Atlantic hurricane season | Seasonal summary
There are six main requirements for tropical cyclogenesis: sufficiently warm sea surface temperatures, atmospheric instability, high humidity in the lower to middle levels of the troposphere, enough Coriolis force to develop a low pressure center, a pre-existing low level focus or disturbance, and low vertical wind shear. While these conditions are necessary for tropical cyclone formation, they do not guarantee that a tropical cyclone will form. Normally, an ocean temperature of 26.5 °C (79.7 °F) spanning through a depth of at least is considered the minimum to maintain the special mesocyclone that is the tropical cyclone. These warm waters are needed to maintain the warm core that fuels tropical systems.
Typhoon | Genesis
"Tropical" refers to the geographical origin of these systems, which form almost exclusively over tropical seas. "Cyclone" refers to their winds moving in a circle, whirling round their central clear eye, with their winds blowing counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere. The opposite direction of circulation is due to the Coriolis effect. Tropical cyclones typically form over large bodies of relatively warm water. They derive their energy through the evaporation of water from the ocean surface, which ultimately recondenses into clouds and rain when moist air rises and cools to saturation. This energy source differs from that of mid-latitude cyclonic storms, such as nor'easters and European windstorms, which are fueled primarily by horizontal temperature contrasts.
Tropical cyclone | Introduction
The storm appears to have formed in the central Gulf of Mexico before moving northeast to make landfall near Clearwater, Florida. It then crossed the Florida peninsula and exited near Cape Canaveral. After moving into the extreme western Atlantic, the cyclone continued to the northeast just offshore of the East Coast of the United States to the Grand Banks of Newfoundland.
1848 Tampa Bay hurricane | Meteorological history
July featured no Atlantic tropical cyclones. Tropical Storm Bertha was the only system to form during August, developing in the Gulf of Mexico. Despite warm sea surface temperatures (SSTs) in the tropical Atlantic, no storms formed during the month, below the climatological average of one. The low monthly activity was in part due to an unfavorable wind pattern which prevailed across the Atlantic for much of the month. In September, however, conditions for tropical cyclogenesis were more favorable, with concomitant cyclonic activity. Four storms formed, of which two attained hurricane strength, higher than the mean activity of the last 70 Septembers.
1957 Atlantic hurricane season | Season summary
The locus of formation for North Atlantic subtropical cyclones is out in the open ocean; the island of Bermuda is regularly impacted by these systems. The South Atlantic environment for formation of subtropical cyclones has both stronger vertical wind shear and lower sea surface temperatures, yet subtropical cyclogenesis is regularly observed in the open ocean in the South Atlantic. A second mechanism for formation has been diagnosed for South Atlantic subtropical cyclones: lee cyclogenesis in the region of the Brazil Current.
Subtropical cyclone | Formation
The origins of Barry can be traced to a mesoscale convective vortex that formed over southwestern Kansas on July 2. On July 5, the Climate Prediction Center noted the possibility for this disturbance to interact with a trough of low pressure over the Southeastern United States, eventually triggering a low pressure area over the Gulf of Mexico. The following day, the National Hurricane Center (NHC) highlighted a low likelihood of tropical cyclogenesis while the disturbance was still centered well-inland over Tennessee, anticipating that the weather system would track into the northern Gulf of Mexico. Over the next few days, the system drifted southeastward towards Georgia, steered by a ridge to its west.
Hurricane Barry (2019) | Meteorological history
Typically, tropical cyclones do not form in the South Atlantic Ocean, due to strong upper level shear, cool water temperatures, and the lack of a convergence zone of convection. Occasionally though, as seen in 1991 and early 2004, conditions can become slightly more favorable. For Catarina, it was a combination of climatic and atmospheric anomalies. Water temperatures on Catarina's path ranged from , slightly less than the temperature of a normal tropical cyclone, but sufficient for a storm of baroclinic origin. Catarina remains the only hurricane strength tropical cyclone ever observed in the South Atlantic Ocean (reliable continuous and relatively comprehensive records only began with the satellite era beginning about 1970).
Hurricane Catarina | Rare formation
In early July, a shortwave trough embedded in the westerlies crossed the United States. The system emerged over the Atlantic near the Outer Banks of North Carolina on July 12; a surface low soon developed. Traversing the Gulf Stream, convection abruptly increased on July 13 and it is estimated that a tropical depression formed by 06:00 UTC that day, roughly 255 mi (410 km) east-northeast of Cape Hatteras. Six hours later, the depression intensified into a tropical storm and was assigned the name "Claudette". The sudden development of the cyclone was not well-forecast, and Claudette was not operationally warned upon until it was already a tropical storm.
2015 Atlantic hurricane season | Tropical Storm Claudette
There are many aspects of this process which remain a mystery. Scientists do not know why a ring of convection forms around the center of circulation instead of on top of it, or why the upper-level anticyclone only ejects a portion of the excess air above the storm. Many theories exist as to the exact process by which the eye forms: all that is known for sure is that the eye is necessary for tropical cyclones to achieve high wind speeds.
Eye (cyclone) | Formation and detection
There are two types of "Gulf Lows": West and East Gulf Cyclones or Types Ga and Gb. As western storms (Alberta clippers, North and South Pacific and Rocky Mountain) move eastward, a trailing frontal remnant is often left in the Gulf of Mexico or the adjacent coastal states. When the frontal trough from a new cyclone enters this area, cyclogenesis often occurs on the Gulf front. This newly formed Gulf wave that moves northeastward and dominates the weather over the eastern United States and Canada. One of the basic differences between the two types is that the Ga track is west of the Appalachians and the Gb track is east of the Appalachians.
Gulf low | Types
Upon first becoming a tropical cyclone, Tropical Storm Fay was moving steadily westward over Hispaniola, influenced by a ridge to its north. At around 1200 UTC on August 16, the storm emerged into the Gulf of Gonâve, with little organized convection near the center. Environmental conditions favored strengthening, and convection quickly developed over the center. By early on August 17, a hurricane hunters flight reported a better organized circulation center, and satellite images displayed well-established outflow within a large convection envelope. After passing near or over southwestern Granma Province in Cuba, upper-level wind shear increased slightly, and the convection diminished near the center.
Tropical Storm Fay (2008) | Meteorological history
A tropical wave moved off the African coast on July 19. The system headed westward through the Atlantic Ocean for the next week with no change in development. After entering the Caribbean Sea on July 26, convection began to come together two days later due to the influence of anticyclonic flow. The disturbance passed the Yucatan Peninsula on July 29 and entered the Gulf of Mexico. No circulation was found in the developing system, however. On July 30, the disturbance turned to the northwest and entered an area of the Gulf with slightly above normal sea surface temperatures and low vertical wind shear, which favored further development.
Tropical Storm Amelia (1978) | Meteorological history
In mid-June, a mid-level center of circulation formed in association with a quasi-stationary cold front that stretched across northern Florida and the extreme northeast Gulf of Mexico. On June 20, a weak and disorganized area of low pressure developed in conjunction with the front and it passed by Tampa Bay, Florida the following day. Upon moving into the eastern Gulf of Mexico, there was little convection observed on satellite imagery, although a distinguishable wind-shift was noted by an offshore buoy. However, by June 23, the presence of deep convection atop a circulation had become well-defined enough for the National Hurricane Center to classify the disturbance as a tropical depression, while centered 330 mi (535 km) southwest of Cape Coral, Florida.
Hurricane Bonnie (1986) | Meteorological history
From the overflow orifice, the coal goes into the overflow chamber, and is discharged to the next stage of the process. Fluid on entry commences in the outer regions of the cyclone body. This combined with rotational motion to which it is constrained creates an outer spiral. The existence of a top central outlet and inability for all the fluid to leave at the cone apex outlet, assist the inward migration of some of the fluid from the external moving mass. The amount of inward migration increases as the apex is neared, i.e. the radius decreased and the fluid which flows in this migratory stream, ultimately reverses its vertical velocity direction and flows upward to the cyclone over flow outlet, i.e.
Coal preparation plant | Dense medium cyclones
On September 5, a frontal trough, the same responsible for the extratropical transition of Tropical Storm Lee, passed through the western Gulf of Mexico before stalling in the central Gulf of Mexico and Bay of Campeche. At the tail-end of the trough, increased shower and thunderstorm activity associated with a developing low-pressure area prompted the National Hurricane Center (NHC) to begin monitoring the disturbance for tropical cyclone formation the next day. The low separated from the front early on September 7, but convection was too disorganized for classification at the time. By 1800 UTC, however, a curved band developed in the western semicircle of the circulation.
Hurricane Nate (2011) | Meteorological history
These warm core cyclones tend to form over the oceans between 10 and 30 degrees of the equator.
Cyclogenesis | Tropical cyclones
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.
Atlantic hurricane | Steering factors
An approaching mid-level trough caused the system to accelerate northeastward across Florida Panhandle, though upon doing so the thunderstorm activity quickly diminished. On July 13, forecasters expected the system to be absorbed by the approaching trough. However, the low pressure area emerged into the western Atlantic Ocean near North Carolina early on July 14, and upon doing so its convection increased and became better organized. The circulation and convection became further defined, and the National Hurricane Center estimates the system developed into Tropical Depression One late on July 14 about 45 miles (75 km) west-southwest of Hatteras, North Carolina. Upon becoming a tropical cyclone, the depression was moving quickly to the east-northeast, due to a deepening mid-level low south of the Canadian Maritimes.
Tropical Storm Arthur (2002) | Meteorological history
Worldwide, tropical cyclone activity peaks in late summer when water temperatures are warmest. Each basin, however, has its own seasonal patterns. On a worldwide scale, May is the least active month, while September is the most active. In the North Atlantic, a distinct hurricane season occurs from June 1 through November 30, sharply peaking from late August through October. The statistical peak of the North Atlantic hurricane season is September 10. The Northeast Pacific has a broader period of activity, but in a similar time frame to the Atlantic. The Northwest Pacific sees tropical cyclones year-round, with a minimum in February and a peak in early September.
Tropical cyclogenesis | Times of formation
A tropical storm formed in the west-central Gulf of Mexico on September 24. After initially moving northwestward, the storm curved east-northeastward by the following day. The cyclone peaked with maximum sustained winds of 60 mph (95 km/h), and due to lack of data, was believed to have maintained this intensity until making landfall near modern-day Panama City, Florida at 13:00 UTC on September 27. By early September 28, the storm weakened to a tropical depression and soon dissipated near the Florida–Georgia state line. Several locations along the Gulf Coast of the United States reported heavy rainfall, with and of precipitation observed in Mobile and New Orleans, respectively.
1875 Atlantic hurricane season | Tropical Storm Four
Tropical Storm Colin was the earliest third named storm in the Atlantic basin on record for 4 years until it was surpassed by Tropical Storm Cristobal in 2020. An atypical, poorly organized tropical cyclone, Colin developed from a low pressure area over the Gulf of Mexico near the northern coast of the Yucatán Peninsula late on June 5, 2016. Moving northward, the depression strengthened into a tropical storm about eight hours after formation. On June 6, Colin curved to the north-northeast and intensified slightly to winds of 50 mph (85 km/h). Strong wind shear prevented further strengthening and resulted in the system maintaining a disheveled appearance on satellite imagery.
Tropical Storm Colin (2016) | Introduction
The lowered pressure acts to draw in air, creating convergence in the low-level wind field. Low-level convergence and upper-level divergence imply upward motion within the column, making cyclones tend to be cloudy. As the cyclone strengthens, the cold front sweeps towards the equator and moves around the back of the cyclone. Meanwhile, its associated warm front progresses more slowly, as the cooler air ahead of the system is denser, and therefore more difficult to dislodge. Later, the cyclones occlude as the poleward portion of the cold front overtakes a section of the warm front, forcing a tongue, or trowal, of warm air aloft.
Extratropical cyclone | Cyclogenesis
On July 27, a tropical depression developed in the northern Gulf of Mexico, about 100 mi (160 km) south of Grand Isle, Louisiana. A map of the low pressure areas forming in July 1954 indicated that the system originated near the Mississippi Delta and tracked southward. After forming, the depression tracked northwestward, intensifying into Tropical Storm Barbara early on July 28. Maximum sustained winds reached 45 mph (75 km/h), although a tanker offshore named the "Henry M. Dawes" reported wind gusts of . Officials at the United States Weather Bureau posted a storm warning from Cameron to Burrwood, Louisiana, and also advised small craft to remain at port along the entire northern Gulf Coast.
1954 Atlantic hurricane season | Tropical Storm Barbara
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.
Atlantic hurricane | July
The name Fernand has been used for two tropical cyclones in the Atlantic Ocean. Both formed in the southwestern Gulf of Mexico.
Tropical Storm Fernand | Introduction
During late June, a frontal trough drifted into the northeastern Gulf of Mexico, and by June 22 a surface circulation formed. Tracking west-northwestward, it developed into Tropical Depression Two on June 23 while located about 330 miles (535 km) south of Pensacola, Florida. The next day, it attained tropical storm status, and with continued favorable conditions attained hurricane status on June 25 to the south of Louisiana. Bonnie turned to the northwest and made landfall near Sea Rim State Park in Texas. The storm quickly weakened over land as it turned to the north and northeast, and on June 28 it was absorbed by an approaching frontal zone in southeastern Missouri.
1986 Atlantic hurricane season | Hurricane Bonnie
Hurricane Four also grew from a tropical storm that formed in the Gulf of Mexico. It brought high winds and flooding to towns along the Gulf coast. This storm also crossed over Florida into the Atlantic and eventually made another landfall at New Brunswick as an extratropical storm. Hurricane Five existed in the tropical Atlantic between September 18 and September 21, without making landfall. Hurricane Six formed as a tropical storm in the Gulf of Mexico and reached hurricane strength off North Carolina a week later on October 2. The cyclone had impacted both Mississippi and Florida as it had travelled north.
1885 Atlantic hurricane season | Season summary
A tropical storm formed in the western Gulf of Mexico on August 29. It moved quickly to the northeast, and made landfall on extreme southeastern Louisiana on the 30th as a 60 mph (97 km/h) tropical storm. After crossing Florida, the storm was last seen off the coast of South Carolina on August 31.
1885 Atlantic hurricane season | Tropical Storm Three
Tropical cyclogenesis resumed with the development of Tropical Depression BOB 03 forming near Andhra Pradesh on October 22. On November 11, a severe cyclonic storm – numbered BOB 04 – developed in the Bay of Bengal. It soon became the strongest tropical cyclone with maximum sustained winds of 100 km/h (65 mph) and a minimum barometric pressure of . BOB 04 made landfall in Bangladesh on November 12, hours before dissipating. Later in November, another cyclonic storm – assigned to BOB 05 – formed in the Bay of Bengal on November 23. It moved northward before eventually curving westward and dissipating on November 28.
2002 North Indian Ocean cyclone season | Season summary
An area of stratiform precipitation develops poleward of the warm front along the conveyor belt. Active precipitation poleward of the warm front implies potential for greater development of the cyclone. A portion of this conveyor belt turns to the right (left in the Southern Hemisphere), aligning with the upper level westerly flow. However, the western portion of this belt wraps around the northwest (southwest in the Southern Hemisphere) side of the cyclone, which can contain moderate to heavy precipitation. If the air mass is cold enough, the precipitation falls in the form of heavy snow. Theory from the 1980s talked about the presence of a cold conveyor belt originating north of the warm front and flowing along a clockwise path (in the northern hemisphere) into the main belt of the westerlies aloft, but there has been conflicting evidence as to whether or not this phenomenon actually exists.
Inflow (meteorology) | Extratropical cyclones
Before the storm formed, sea surface temperatures were above normal in the Bay of Campeche and tropical eastern Pacific Ocean. After Hurricane Earl developed and moved away from the region, a broad area of low pressure formed in the southwest Caribbean on September 4. It moved to the northwest and slowly organized in the Gulf of Mexico, although a series of tropical waves prevented rapid development. By September 8, there was a large area of convection located over the western Gulf of Mexico. That day, the system developed into Tropical Depression Six while east-southeast of Brownsville, Texas. Initially, the depression was large, without a well-defined center of circulation.
Tropical Storm Frances (1998) | Meteorological history
Areas farther than 30 degrees from the equator (except in the vicinity of a warm current) are not normally conducive to tropical cyclone formation or strengthening, and areas more than 40 degrees from the equator are often very hostile to such development. The primary limiting factor is water temperatures, although higher shear at increasing latitudes is also a factor. These areas are sometimes frequented by cyclones moving poleward from tropical latitudes. On rare occasions, such as Pablo in 2019, Alex in 2004, Alberto in 1988, and the 1975 Pacific Northwest hurricane, storms may form or strengthen in this region. Typically, tropical cyclones will undergo extratropical transition after recurving polewards, and typically become fully extratropical after reaching 45–50˚ of latitude.
Tropical cyclogenesis | Middle latitudes
In rare cases, they become warm-core tropical cyclones. Upper cyclones and the upper troughs that trail tropical cyclones can cause additional outflow channels and aid in their intensification. Developing tropical disturbances can help create or deepen upper troughs or upper lows in their wake due to the outflow jet emanating from the developing tropical disturbance/cyclone.
Cyclone | TUTT cell
Eventually, the cyclone will become barotropically cold and begin to weaken. Atmospheric pressure can fall very rapidly when there are strong upper level forces on the system. When pressures fall more than per hour, the process is called explosive cyclogenesis, and the cyclone can be described as a bomb. These bombs rapidly drop in pressure to below under favorable conditions such as near a natural temperature gradient like the Gulf Stream, or at a preferred quadrant of an upper-level jet streak, where upper level divergence is best. The stronger the upper level divergence over the cyclone, the deeper the cyclone can become.
Extratropical cyclone | Cyclogenesis
The Atlantic Ocean began an organization favorable to the sea surface temperatures due to dissipation of the 2010-12 La Niña event. The Northern Hemisphere, nineteen tropical cyclones formed in the Atlantic hurricane season, the third-most active in history with previous 1887, 1995, 2010 and 2011 seasons.
Tropical cyclones in 2012 | North Atlantic Ocean
The Gulf Stream, together with its northern extension the North Atlantic Drift, is a warm and swift Atlantic ocean current that originates in the Gulf of Mexico and stretches to the tip of Florida, and follows the eastern coastlines of the United States and Newfoundland before crossing the Atlantic Ocean as the North Atlantic Current. The process of western intensification causes the Gulf Stream to be a northwards accelerating current off the east coast of North America. At about , it splits in two, with the northern stream, the North Atlantic Drift, crossing to Northern Europe and the southern stream, the Canary Current, recirculating off West Africa.
Gulf Stream | Introduction
In the south-west Indian Ocean, tropical cyclones form south of the equator and west of 90° E to the coast of Africa.
South-West Indian Ocean tropical cyclone | Introduction
CST), storms associated with the wave organized into a tropical depression based on ship reports in the bay; at the time, the first indication of a developing tropical cyclone originated from a report from a shrimp boat. The depression was in a highly favorable environment for intensification in the western Gulf of Mexico; sea surface temperatures in the area were at , or 3 °F (2 °C) above normal for the time of year. In addition, the latitudinal alignment of a polar trough over the Great Plains and the nascent disturbance in the Bay of Campeche created an environment suitable for outflow in the upper-levels of the atmosphere.
Hurricane Audrey | Meteorological history
The National Hurricane Center (NHC) first noted the potential of the formation of a tropical cyclone in the Gulf of Mexico during the mid-afternoon hours of June 12. At the time, an upper-level trough was producing disorganized showers and thunderstorms over the northwestern Caribbean Sea, Belize, and the Yucatán Peninsula. However, the NHC assessed a low probability as atmospheric conditions were assessed to be unfavorable in the Gulf of Mexico. Moving northwestward, the system tracked over the Yucatán Peninsula, and development chances increased as forecasts showed a more favorable environment within the Gulf of Mexico. Early on June 14, the trough began to interact with an upper-level low over the Gulf of Mexico, producing additional showers over portions of Central America.
Tropical Storm Bill (2015) | Meteorological history
Hurricane Fay originated in a disturbance calved from a mid- to upper-level trough over the east-central Atlantic. On October 7, a broad region of showers and thunderstorms formed around it, possibly enhanced by moisture from a tropical wave to the south. Tracking westward, the energy coalesced into an upper-level cold-core low on the following day, and an associated trough formed at the surface. Southwesterly wind shear initially hindered development, but as the system became more vertically aligned on October 9, the hostile winds calmed. In turn, a curved banding feature was able to take form. Early on October 10, satellite imagery indicated that the center of circulation had become better-defined, with a swath of deep convection to the north and west of the low.
Hurricane Fay | Meteorological history
The interaction of the trough and a ridge to the east increased wind shear, causing the storm to weaken. On February 24, the storm became extratropical while still maintaining a well-defined circulation. It slowed and looped back to the northwest due to a ridge to the south, gradually becoming less defined and dissipating on February 26.
1999–2000 South-West Indian Ocean cyclone season | Severe Tropical Storm Felicia
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.
Atlantic hurricane | Climatology
Wind shear within the Gulf of Mexico was weak and remained favorable to tropical cyclone formation. A reconnaissance flight later that day discovered an ill-defined circulation which led to low confidence of the location of the center of circulation. However, enough convection persisted for the depression to be upgraded into Tropical Storm Fay that evening. Stationary in movement, the associated convection became removed from the center of circulation; despite this, the system gradually intensified. On September 6, the storm reached its peak intensity of 60 mph (100 km/h). Light wind shear prevented Fay from intensifying further, and the gradual movement was dictated by a weak mid-level ridge to the north.
Tropical Storm Fay (2002) | Meteorological history
A minimum distance of 500 km (300 mi) from the equator is normally needed for tropical cyclogenesis. Whether it be a depression in the Intertropical Convergence Zone (ITCZ) or monsoon trough, a broad surface front, or an outflow boundary, a low level feature with sufficient vorticity and convergence is required to begin tropical cyclogenesis. About 85 to 90 percent of Pacific typhoons form within the monsoon trough. Even with perfect upper-level conditions and the required atmospheric instability, the lack of a surface focus will prevent the development of organized convection and a surface low. Vertical wind shear of less than 10 m/s (20 kn, 33 ft/s) between the ocean surface and the tropopause is required for tropical cyclone development.
Typhoon | Genesis
Vertical wind shear of less than 10 m/s (20 kt, 22 mph) between the surface and the tropopause is favored for tropical cyclone development. A weaker vertical shear makes the storm grow faster vertically into the air, which helps the storm develop and become stronger. If the vertical shear is too strong, the storm cannot rise to its full potential and its energy becomes spread out over too large of an area for the storm to strengthen. Strong wind shear can "blow" the tropical cyclone apart, as it displaces the mid-level warm core from the surface circulation and dries out the mid-levels of the troposphere, halting development.
Tropical cyclogenesis | Weak vertical wind shear
On July 24, a tropical wave emerged from the east coast of Africa, near the Cape Verde Islands. The wave was disorganized and failed to develop convection as it traversed the Atlantic Ocean over the next several days. The wave eventually entered the Eastern Pacific basin on August 2, and interacted with a broad area of cyclonic flow located a few hundred miles south of Mexico. The wave became better organized throughout the day, and an area of low pressure formed 660 mi (1060 km) south of Manzanillo, Mexico on August 5. Strong convection began to develop. That day, a banding feature formed On the morning of August 6, a Tropical Cyclone Formation Alert was issued.
Hurricane Hernan (2008) | Origins
If the associated jet stream is stronger than normal and there is colder than normal air in place in central Canada to provide a greater than normal temperature contrast with Gulf of Mexico moisture drawn northward by the developing panhandle low, surface cyclogenesis can be particularly energetic and cause a great swath of heavy snow to develop and blanket a large portion of the American Great Plains and upper-midwestern states in conjunction with very strong winds, the combination of which exceeds blizzard criteria. Over the Great Lakes, the interaction of these storms with the lakes can amplify windspeeds causing extreme heavy sometimes localized snowfall, thundersnow and often shoreline erosion.
Panhandle hook | Formation