The Gulf Stream proper is a western-intensified current, driven largely by wind stress. The North Atlantic Drift, in contrast, is largely driven by thermohaline circulation. In 1958, oceanographer Henry Stommel noted that "very little water from the Gulf of Mexico is actually in the stream". By carrying warm water northeast across the Atlantic, it makes Western Europe and especially Northern Europe warmer than it otherwise would be.
Properties
Gulf Stream
Gulf Stream | Properties
It is a western-intensified current, driven largely by wind stress. The Gulf stream is a western-intensified current, driven largely by wind stress. The North Atlantic current, in contrast, is largely driven by thermohaline circulation. Western-intensified current and is largely driven by thermohaline circulation. A western-intensified current, driven largely by wind stress.
what does gulf stream refer to?
user
It is a warm and swift Atlantic ocean current
assistant
where does it originate?
user
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.
assistant
does it help a cyclone to form?
user
Its presence has led to the development of strong cyclones of all types, both within the atmosphere and within the ocean.
assistant
does it have any specific properties?
user
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
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
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
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
The development of a significant mesoscale convective complex can send out a large enough outflow boundary to weaken the cyclone as the tropical cyclone center moves into the more stable air mass behind the leading edge of thunderstorm outflow, or outflow boundary. Moderate vertical wind shear can lead to the initial development of the convective complex and surface low similar to the mid-latitudes, but it must relax to allow tropical cyclogenesis to continue. While the most obvious motion of clouds is toward the center, tropical cyclones also develop an upper-level (high-altitude) outward flow of clouds. These originate from air that has released its moisture and is expelled at high altitude through the "chimney" of the storm engine.
Outflow (meteorology) | Tropical cyclones
During the next couple of days, strong upper level winds stripped deep convection away from the center with the JTWC downgrading the cyclone to a tropical depression early on January 19. The remaining low level circulation center slowly dissipated with the JTWC issuing their final advisory early the next day. The cyclone posed a direct threat to Coalition forces, which were operating in the Arabian Sea, Persian Gulf and the Red Sea, in the buildup to the Gulf war. However it was not a significant factor in the buildup to the Gulf war and due to it low latitude track and weak intensity it had little effect on ships steaming to the Middle East.
1991 North Indian Ocean cyclone season | Tropical Storm 01A
Although there has been recent debate, there is consensus that the climate of Western Europe and Northern Europe is warmer than it would otherwise be due to the North Atlantic drift, one of the branches from the tail of the Gulf Stream. 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.
Thermohaline circulation | Gulf Stream
The Gulf is also a breeding ground for cyclones during the period between November and April. In September and October the Morning Glory Cloud appears in the Southern Gulf. The best vantage point to see this phenomenon is in the Burketown area shortly after dawn.
Gulf Country | Climate
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
The Gulf Stream proper is a western-intensified current, driven largely by wind stress. The North Atlantic Drift, in contrast, is largely driven by thermohaline circulation. In 1958, oceanographer Henry Stommel noted that "very little water from the Gulf of Mexico is actually in the stream". By carrying warm water northeast across the Atlantic, it makes Western Europe and especially Northern Europe warmer than it otherwise would be.
Gulf Stream | Properties
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
The addition of fresh water to northern oceans may reduce the strength of the Gulf stream, and allow a southwards current to develop instead. This would cause the cooling of the northern hemisphere, and the warming of the southern, causing changes in ice accumulation and melting rates and possibly triggering shelf destruction and Heinrich events (Stocker 1998).
Heinrich event | External forcings
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
The combined flow of these gyres acts to advect the storm slowly poleward and westward. This effect occurs even if there is zero environmental flow.
Tropical cyclone | Beta drift
Despite near normal water temperatures over the Arabian Sea, no storms developed in that portion of the basin. Convection was also lower than normal across the Bay of Bengal. The main factor against tropical cyclogenesis was persistently unfavorable wind shear. Overall, there were six depressions, five of which intensified into a cyclonic storm, which has maximum sustained winds of at least 65 km/h (40 mph).
2000 North Indian Ocean cyclone season | Season 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
However, it is still possible for tropical systems to form within this boundary as Tropical Storm Vamei and Cyclone Agni did in 2001 and 2004, respectively.
Tropical cyclone | Locations
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
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
The storm was located over the warm waters of the Gulf Stream and in an area of light to moderate wind shear. These environmental factors favored some intensification. The elongated circulation of the developing storm was steered generally northward by a ridge over the western Atlantic Ocean and an approaching trough on the opposite side. Fay strengthened slightly on July 10, despite southwesterly wind shear which exposed the circulation from the main area of thunderstorms, causing it to entrain dry air. That day at 15:00 UTC, the NHC estimated peak winds of 60 mph (95 km/h). At that time, Fay had a small circulation center just east of the Delmarva peninsula, which was rotating around a larger circulation with subtropical appearance on visible satellite imagery.
Tropical Storm Fay (2020) | Meteorological history
On December 4, analysis showed that Ockhi was maintaining a source aloft, but there was restricted outflow on the western edge, due to a deepening trough advancing rapidly from the west. Increasing vertical wind shear along with a deep layered subtropical ridge to the east steered it north-northeast, and a dry air intrusion from the west gradually weakened the system. On the following day, the power of the storm quickly lessened as it encountered increasingly unfavorable conditions, including high wind shear. As Ockhi became embedded within a deep mid-latitude trough, the storm rapidly underwent an extratropical transition. Dry and cold air from the subcontinent rapidly weakened the storm, and it was last noted as a well-marked low-pressure area south of the Gulf of Cambay on December 6.
Cyclone Ockhi | Meteorological history
During the next few days, the tropical depression strengthened slowly as it slowly moved towards the eastern border of the Indian Ocean. During this time, convection around the disturbance increased, but failed to organize around the storm's low level circulation center. Despite these unfavorable conditions, the storm managed to develop convection around its area of low pressure, and organized itself significantly. On , the Thai and Malaysian meteorological departments (TMD) reported that the disturbance had developed into a tropical depression, and initiated advisories on the system. From continuing into , the storm strengthened slightly as it continued moving towards the Indian Ocean, but not enough for it to become a tropical storm.
Cyclone Jal | Meteorological history
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
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
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
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
The National Oceanic and Atmospheric Administration (NOAA) operates a GIV-SP (N49RF) modified to fly scientists and crew members at 45,000 feet around tropical cyclones. The aircraft was modified to drop instruments called "dropsondes" to measure windspeed, barometric pressure, humidity, and temperature as they fall to the surface of the ocean. By sampling the cyclone with these dropsondes over a 4,000 mile track around the storm, the forecasters at NOAA's National Hurricane Center and Hurricane Research Division can better predict where the hurricane will be "steered" by the upper level winds. They also predict wind shear that will either increase or decrease a hurricane's strength.
Gulfstream IV | Operational history
A tropical disturbance was observed on November 19 about 800 km (500 mi) southeast of Colombo, Sri Lanka in the Bay of Bengal. The disturbance tracked westward, weakening after passing south of Sri Lanka. It entered the Arabian Sea on November 26, and despite being located unusually close to the equator, the system maintained convection about its circulation, aided by low wind shear. While the system was organizing, the center crossed the equator to reach about 0.5° S, thus becoming an anticyclonic circulation in the southern hemisphere. This was unusual, as the Coriolis effect is nonexistent along the equator—the Coriolis effect refers to planetary vorticity, which provides the spin in a cyclone.
2004 North Indian Ocean cyclone season | Severe Cyclonic Storm Agni
In 2007, the National Aeronautics and Space Administration (NASA) hypothesized that the wind shear between the eye and the eyewall could enhance updraft through the center of a cyclone and generate convection. Hot towers may appear when a cyclone is about to intensify, possibly rapidly. A particularly tall hot tower rose above Hurricane Bonnie in August 1998, as the storm intensified before striking North Carolina.
Hot tower | Effects on tropical cyclones
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
Toward the end of May 2010, a surge in the monsoon produced widespread convection, or thunderstorms, off the southwest coast of India in the southeastern Arabian Sea. After a low-level circulation became evident on May 30, the India Meteorological Department (IMD) designated the system as a low pressure area. The low moved northwestward within an area of warm water temperatures of , moderate wind shear, and an upper-level environment conducive for tropical cyclogenesis, The Joint Typhoon Warning Center (JTWC) first noted the system on May 30 as an area of potential development. The circulation became more defined within the building convection, which was amplified by outflow from an anticyclone over the northern Arabian Sea.
Cyclone Phet | Meteorological history
For example, the size, intensity, moist-convection, surface evaporation, the value of potential temperature at each potential height can affect the nonlinear evolution of a vortex.
Cyclone | Introduction
An eye-like structure is often found in intensifying tropical cyclones. Similar to the eye seen in hurricanes or typhoons, it is a circular area at the circulation center of the storm in which convection is absent. These eye-like features are most normally found in intensifying tropical storms and hurricanes of Category 1 strength on the Saffir-Simpson scale. For example, an eye-like feature was found in Hurricane Beta when the storm had maximum wind speeds of only 80 km/h (50 mph), well below hurricane force. The features are typically not visible on visible wavelengths or infrared wavelengths from space, although they are easily seen on microwave satellite imagery.
Eye (cyclone) | Eye-like features
The same trough that pushed the storm across Florida had moved to the north, allowing for high pressure to develop in the upper levels of the atmosphere. Deemed a "hybrid storm", the cyclone rapidly intensified in warm waters of up to from the Gulf Stream combined with a cold air mass over the United States. The system continued to rapidly intensify while moving within the Gulf Stream; it developed central convection, an unusual trait for an extratropical cyclone, and at one point exhibited an eye. Despite these indications of tropical characteristics, "There was no front associated with it and it had a warm core, but the radius of maximum winds was more than , so under the standard NHC criteria it didn't qualify as a tropical storm." On December 23 and 24, the nor'easter intensified to attain a barometric pressure of .
Christmas 1994 nor'easter | Meteorological history
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
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
There are a number of structural characteristics common to all cyclones. A cyclone is a low-pressure area. A cyclone's center (often known in a mature tropical cyclone as the eye), is the area of lowest atmospheric pressure in the region. Near the center, the pressure gradient force (from the pressure in the center of the cyclone compared to the pressure outside the cyclone) and the force from the Coriolis effect must be in an approximate balance, or the cyclone would collapse on itself as a result of the difference in pressure. Because of the Coriolis effect, the wind flow around a large cyclone is counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere.
Cyclone | Structure
While Megh was in its formative stages, it developed broken rainbands that swirled into the circulation center, which was located beneath the blossoming convection. On November 6, dry air began to become entrained into the circulation, although the unfavorable conditions did not disrupt the center. Instead, the convection became better organized, developing into a central dense overcast, as well as the beginnings of an eye feature. As the storm continued to develop, the radius of maximum winds shrank, resulting in a smaller storm than the previous Cyclone Chapala. At 12:00 UTC on November 7, the JTWC upgraded Megh to the equivalent of a hurricane after a small defined eye became evident.
Cyclone Megh | Meteorological history
Despite the intensification, the storm remained poorly organized due to strong wind shear, with the low-level center being indistinguishable on infrared satellite imagery. Early on June 6, data from surface observations, the National Oceanic and Atmospheric Administration, and a reconnaissance aircraft flight suggested that two small-scale circulations existed. Shortly thereafter, NHC noted that the "satellite presentation of Colin does not resemble that of a classical tropical cyclone", as convection and strong winds were displaced well east of the center, primarily due to wind shear.. The storm began accelerating to the northeast late on June 6 due to a mid- to upper-level trough over the Midwestern United States.
Tropical Storm Colin (2016) | Meteorological history
Dry air within its circulation initially kept Ana weak, with sparse thunderstorm activity. However, the warm waters of the Gulf Stream, coupled with atmospheric instability resulting from cold temperatures aloft, enabled the formation of curved banding features near the storm's core. At the same time, the wind field constricted, indicating an imminent transition to a fully tropical storm. Late on May 8, Ana attained its peak intensity with maximum sustained winds of and a minimum central pressure of 998 mbar. By the next morning, most of the convection on the storm's periphery dissipated; with persistent thunderstorms near the center and favorable anticyclonic outflow, Ana became a tropical storm about to the southeast of Myrtle Beach.
Tropical Storm Ana (2015) | Meteorological history
However, this relationship is indirect via the large-scale dynamics of the tropics; the direct influence of the absolute sea surface temperature on formula_7 is weak in comparison.
Tropical cyclone | Characteristic values and variability on Earth
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
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.
Gulf Stream | Introduction
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
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
A waterspout is a columnar vortex forming over water that is, in its most common form, a non-supercell tornado over water that is connected to a cumuliform cloud. While it is often weaker than most of its land counterparts, stronger versions spawned by mesocyclones do occur.
Cyclone | Waterspout
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 January 15, a tropical disturbance began organizing near the Chagos Archipelago in the South Indian Ocean convergence zone, which is an extended area of convection connected to the monsoon. The thunderstorms gradually organized, associated with a weak circulation and located within an area of moderate wind shear. A distinct low pressure area developed on January 16, about east of Diego Garcia. The thunderstorms were primarily located along the western periphery due to continued shear, and ordinarily would prevent significant development. The system moved to the southwest along the north side of a ridge, and despite the shear it developed into a tropical disturbance late on January 16.
Cyclone Dina | Meteorological history
Initially, the cloud pattern associated with the system featured a tight and well-defined circulation, as well as clusters of deep convection south of the center. Due to the proximity of a large upper-level low-pressure area in the southern Gulf of Mexico, the surrounding environment did not favor intensification. Influenced by the low, the depression moved southward. The system completed a cyclonic loop in the central gulf, and by early on September 18 was drifting northward. As a result of wind shear, the center of circulation was separated from the deep convective activity. Early the next day, deep convection persisted in a small area northeast of the center.
Tropical Storm Hermine (1998) | 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
It was noted that these episodes were likely to be associated with a convective system near the tip of the Baja peninsula such as a tropical cyclone or an easterly wave.
Gulf of California moisture surge | Introduction
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
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
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
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
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
A "moat" in a tropical cyclone is a clear ring outside the eyewall, or between concentric eyewalls, characterized by subsidence—slowly sinking air—and little or no precipitation. The air flow in the moat is dominated by the cumulative effects of stretching and shearing. The moat between eyewalls is an area in the storm where the rotational speed of the air changes greatly in proportion to the distance from the storm's center; these areas are also known as "rapid filamentation zones". Such areas can potentially be found near any vortex of sufficient strength, but are most pronounced in strong tropical cyclones.
Eye (cyclone) | Moats
The following day, a steering ridge to the south of the system strengthened and pushed the cyclone away from the coast and to the northwest. At the same time, the system continued to intensify due to the favourable environment in the upper atmosphere. However, hot, dry air flowing into the system from the south, combined with vertical wind sheer, kept the storm from strengthening as much at its maximum potential rate. By 19 March Fay's track had turned to the west-southwest, and over the next day it continued to strengthen in due to favourable upper level outflow and weak vertical sheer.
Cyclone Fay | Meteorological history
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. This is because air must be converging towards the low pressure at the surface which then forces the air to rise very rapidly in the eyewall of the storm, and due to conservation of mass requires a divergence of wind at the top of the troposphere. This process is aided by an upper-level anticyclone which helps channel this air away from the cyclone efficiently. Hot towers have been implicated in tropical cyclone rapid intensification, though they have diagnostically seen varied impacts across basins.
Rapid intensification | Internal
However, several hours over the warm waters of the western Gulf provided the energy needed for Emily to regenerate, and by midnight wind speeds were increasing. The increase in wind speed stalled, but the storm continued to become better organized. Emily started to show very symmetrical outflow, but the hurricane's strongest winds were being found at three different distances from the center. However, the outer wind radii subsided in the end, and the inner core prevailed. The result was a rapid strengthening of the inner core on the evening of July 19. The pressure dropped about 30 millibars and the winds went from 90 mph (145 km/h) to more than 125 mph (200 km/h), all within a few hours.
Hurricane Emily (2005) | Meteorological history
There is a tendency for storms to move very slowly over the region, allowing them to produce tremendous amounts of rain over an extended period, as occurred during Tropical Storm Claudette in 1979, and Tropical Storm Allison in 2001. The area is a very flat flood plain at shallow gradient, slowly draining rainwater through an intricate network of channels and bayous to the sea. The main waterways, the San Jacinto River and the Buffalo Bayou, meander slowly, laden with mud, and have little capacity for carrying storm water.
Hurricane Harvey | Environmental factors
On May 31, a weak circulation persisted over the warm waters of the Gulf of Aden. It moved east-northeastward along the coast of Yemen and Oman, bringing dry air from the north which decreased the convection. The system moved farther offshore on June 7 into the open Arabian Sea, where it interacted with the south-west monsoon and developed more convection. The convection became more persistent by June 9 about 1,480 km (920 mi) northeast of Somalia by June 9. Moving northwestward, the system organized enough for the JTWC to classify it as Tropical Cyclone 02A about 160 km (100 mi) from the Oman coastline.
1996 North Indian Ocean cyclone season | Tropical Storm 02A
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
At 00:00 UTC on October 25, the India Meteorological Department (IMD) classified the system as a depression about 1270 km (790 mi) southeast of Muscat, Oman. When the system first formed, it benefited from warm water temperatures of and a favorable phase of the Madden–Julian oscillation. Moderate wind shear and continued interaction with the monsoon dislocated the bulk of the deepest convection to the western periphery. By 12:00 UTC on October 25, the system organized enough for the JTWC to classify it as Tropical Cyclone 04A, and there were hints of an eye feature within the thunderstorms. By the time of classification, the storm was moving to the northeast, steered by the subtropical ridge to the south, although the motion slowed on October 26 due to competing influence of another subtropical ridge to the northwest.
Cyclone Nilofar | 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
The system then made landfall along the coast of the southern side of the gulf later that day.
Cyclone Harvey | Meteorological history
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
In late April 2002, an area of convection, or thunderstorms, persisted to the west-southwest of Diego Garcia in the south-central Indian Ocean, associated with a trough near the equator. The system had a broad circulation, and initially moved slowly to the east-southeast. It developed due to an increase in the Madden–Julian oscillation (MJO), which moved eastward across the Indian Ocean. The same system spawned a disturbance in the northern Indian Ocean that later struck Oman as a tropical cyclone. Such simultaneous systems in opposite hemispheres occasionally occur in the spring or autumn; in May 2002, the powerful MJO pulse produced two such sets of storms, later producing a set in the eastern Indian Ocean that became a deep depression that struck Myanmar and Tropical Storm Errol to the southwest of Indonesia.
Cyclone Kesiny | Meteorological history
They report that they were successful in simulating key features of Katrina in the control run including the minimum central pressure and maximum wind speeds. When the warm rain processes were removed, the cloud water content naturally increased and the rain water content decreased. The warm rain suppression also changes the thermodynamic structure of the hurricane: temperatures are decreased at low levels at the outer edge of the hurricane. Later, the peak winds decreased along with the central pressure. Zhu and Zhang (2006) used a mesoscale model to simulate the 1998 Hurricane Bonnie. They report that their control run was reasonably able to simulate the observed hurricane.
Hurricane dynamics and cloud microphysics | Intensity
Convective complexes associated with these waves can form tropical cyclones. If the jet is south of its normal location during August and September, tropical cyclogenesis is suppressed. If desertification continues across Sub-Saharan Africa, the strength of the jet could increase, although tropical wave generation probably would decrease, which would decrease the number of tropical cyclones in the Atlantic basin.
African easterly jet | Introduction
With low wind shear and diffluence aloft, the JTWC remarked the system had a fair chance of developing. While the system was organizing, the center crossed the equator to reach about 0.5° S, thus becoming an anticyclonic circulation in the southern hemisphere. This was unusual, as the Coriolis effect is nonexistent along the equator—the Coriolis effect refers to planetary vorticity, which provides the spin in a cyclone. The JTWC later assessed the system as remaining in the northern hemisphere, reaching as far south as 0.7° N, or about 80 km (50 mi) from the equator. After the circulation organized further beneath the convection, the JTWC issued another TCFA at 0300 UTC on November 28.
Cyclone Agni | Meteorological history
Upon entering the Gulf of Mexico, the depression encountered strong wind shear from the outflow of Tropical Storm Fay. Edouard generated minimal amounts of intermittent convection along the southeastern portion of its circulation, enough for it to remain a tropical cyclone. By September 6 the remaining convection dissipated, and Edouard dissipated while becoming absorbed into the larger circulation of Tropical Storm Fay.
Tropical Storm Edouard (2002) | Meteorological history
Convective banding completely encircled the LLCC but never managed to consolidate over the LLCC because of the strong upper-lever cyclone over the storm. Talas was being steered by a mid-level anticyclone, a part of the developing omega block. On September 1, Talas developed a large annulus of nearly in diameter with multiple weak circulations cyclonically rotating around a centroid within the center. Fragmented deep convective banding broadly wrapped the low-level circulation center with an upper-level cyclone over the center and anticyclonic flow around the periphery of the storm.
Tropical Storm Talas (2011) | 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
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
In order for rapid intensification to occur, several conditions must be in place. Water temperatures must be extremely warm (near or above 30 °C, 86 °F), and water of this temperature must be sufficiently deep such that waves do not churn deeper cooler waters up to the surface. Wind shear must be low; when wind shear is high, the convection and circulation in the cyclone will be disrupted. Dry air can also limit the strengthening of tropical cyclones.
Rapid intensification | External
The existence of a significant Coriolis force allows the developing vortex to achieve gradient wind balance. This is a balance condition found in mature tropical cyclones that allows latent heat to concentrate near the storm core; this results in the maintenance or intensification of the vortex if other development factors are neutral.
Tropical cyclogenesis | Coriolis force
In the western North Pacific, there are strong reciprocal relationships between the areas of formative tropical cyclones and that of the lower tropospheric monsoon troughs and the tropical upper tropospheric trough. Tropical cyclone movement can also be influenced by TUTT cells within of their position, which can lead to non-climatological tropical cyclone tracks.
Upper tropospheric cyclonic vortex | Interaction with tropical cyclones
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
The cyclone developed a concentric eye feature, which is an eyewall outside the inner dominant eyewall, with warm waters aiding in further intensification. Early on 29 April, the JTWC estimated Nargis reached winds of 160 km/h (100 mph), and at the same time, the IMD classified the system as a very severe cyclonic storm. Initially, the cyclone was forecast to strike Bangladesh or southeastern India. Subsequently, the cyclone became disorganised and weakened due to subsidence and drier air; as a result, deep convection near the center markedly decreased. At the same time, the storm began a motion to the northeast, around the periphery of a ridge to its southeast.
Cyclone Nargis | Meteorological history
From :
Gulf Winds | Introduction
The resulting Sverdrup transport is equatorwards. Because of conservation of potential vorticity caused by the northwards-moving winds on the subtropical ridge's western periphery and the increased relative vorticity of northwards moving water, transport is balanced by a narrow, accelerating polewards current. This flows along the western boundary of the ocean basin, outweighing the effects of friction with the western boundary current, and is known as the Labrador Current. The conservation of potential vorticity also causes bends along the Gulf Stream, which occasionally break off as the Gulf Stream's position shifts, forming separate warm and cold eddies. This overall process, known as western intensification, causes currents on the western boundary of an ocean basin, such as the Gulf Stream, to be stronger than those on the eastern boundary.
Gulf Stream | Formation and behaviour
The system's central pressure fell to by 00:00 UTC on March 13. A powerful low-level jet over eastern Cuba and the Gulf of Mexico enhanced a cold front extending from the low southward to the Isthmus of Tehuantepec. Furthermore, the subtropical jet stream was displaced unusually far south, reaching into the Pacific Ocean near Central America and extending toward Honduras and Jamaica. Intense ageostrophic flow was noted over the southern United States, with winds flowing perpendicular to isobars over Louisiana. As the area of low pressure moved through the central Gulf of Mexico, a short wave trough in the northern branch of the jet stream fused with the system in the southern stream, which further strengthened the surface low.
1993 Storm of the Century | Meteorological history
In addition, invests in the North Indian Ocean cyclone basin are also labelled by the JTWC, and are suffixed with "A" if they form in the Arabian Sea and with "B" if they form in the Bay of Bengal. The Naval Research Laboratory's Marine Meteorology Division also uses the "Q" suffix to designate invests which form in the South Atlantic Ocean, even though it is not recognized as an official tropical cyclone basin by the World Meteorological Organization.
Invest (meteorology) | Designation
Their development at the middle levels of the atmosphere is similar to the formation of a complete eye, but the features might be horizontally displaced due to vertical wind shear.
Eye (cyclone) | Eye-like features
The cyclone became embedded within a mid- to-upper-level trough between the ridge over the central U.S. and the ridge over the northwestern Caribbean. A strong, upper-level cyclonic shear axis extended from just south of Cape Hatteras to near Brownsville, Texas, which prevented Barry from accelerating in forward speed. The ridge over the United States weakened, thus collapsing the steering pattern; this resulted in a west-southwestward drifting motion of the tropical storm by around August 3. Early on August 3, strong westerly winds prevailed, and separated the center of circulation from what limited convection remained. The storm quickly regained some convection, although maximum sustained winds remained weak, at about 40 mph (60 km/h).
Tropical Storm Barry (2001) | 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
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
At the center of a mature tropical cyclone, air sinks rather than rises. For a sufficiently strong storm, air may sink over a layer deep enough to suppress cloud formation, thereby creating a clear "eye". Weather in the eye is normally calm and free of clouds, although the sea may be extremely violent. The eye is normally circular and is typically in diameter, though eyes as small as and as large as have been observed. The cloudy outer edge of the eye is called the "eyewall". The eyewall typically expands outward with height, resembling an arena football stadium; this phenomenon is sometimes referred to as the "stadium effect".
Tropical cyclone | Eye and center
Gangopadhyay et al. have derived a ten-year time series of the latitude of the separation of the Gulf Stream from the 1970s to the 1980s. By applying empirical orthogonal function analysis to temperatures at 200 metres, Joyce et al. in 2001 constructed a similar index to the GSNW index extending back to the 1950s.
Latitude of the Gulf Stream and the Gulf Stream north wall index | History
The ERC and other atmospheric factors are why Rita did not reintensify when subsequently passing over the eddy vortex. Also of note: tropical depressions, tropical storms, and hurricanes gain strength from, but are not steered by, the temperature of the water. They are steered by the atmosphere, and the atmospheric level involved in steering a hurricane is different at different intensities (i.e., it relates to the minimum pressure of the hurricane).
Loop Current | Process
Though the weakening, Water vapour imagery showed that the typhoon was still maintaining excellent outflow towards the equator and improving outflow towards the pole. Nesat maintained a relatively large area of gale-force winds. Animated infrared satellite imagery depicted that the storm was expanding in size and convective banding continued to move further and further away from the LLCC. The LLCC was also relatively large, elongated and cloud free.
Typhoon Nesat (2011) | Meteorological history
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
In smaller systems, the development of a significant mesoscale convective complex in a sheared environment can send out a large enough outflow boundary to destroy the surface cyclone. Moderate wind shear can lead to the initial development of the convective complex and surface low similar to the mid-latitudes, but it must relax to allow tropical cyclogenesis to continue.
Tropical cyclogenesis | Weak vertical wind shear
After bands of atmospheric convection had wrapped into the systems low level circulation center and formed an eye feature. Later that day, the IMD reported that the system had become a very severe cyclonic storm, before the JTWC reported that Phailin had become equivalent to a Category 4 hurricane on the SSHWS, after it had rapidly intensified throughout that day. Early the next day the system underwent an eyewall replacement cycle and formed a new eyewall which subsequently consolidated. After the new eyewall had consolidated the system slightly intensified further, with the JTWC reporting that the system had reached its peak intensity, with 1-minute sustained wind speeds of which made it equivalent to a Category 5 hurricane on the SSHWS.
Cyclone Phailin | Meteorological history
However, on April 27, the system moved under a subtropical ridge and conditions quickly became favorable for intensification. The presence of the ridge greatly enhanced the outflow over the cyclone and an eye developed by 1200 UTC. By this time, both the JTWC and IMD estimated Mala to have attained hurricane-force winds with the latter classifying it as a "very severe cyclonic storm". The previously weak steering currents became more established as well, with the storm now tracking northeast toward Myanmar through a weakness in a ridge over Southeast Asia. Situated in an area with sea surface temperatures of , the cyclone was able to undergo rapid intensification as wind shear abruptly diminished.
Cyclone Mala | Meteorological history
Storms with pinhole eyes are prone to large fluctuations in intensity, and provide difficulties and frustrations for forecasters.
Eye (cyclone) | Structure
Warm low-level advection–transfer of heat through air or sea–caused by a large-scale low over the western Mediterranean was a primary factor in the rise of strong convection. The presence of a mid- to upper-level cut-off cold-core low, a method of formation typical to medicanes, was also key to the development of intense thunderstorms within the cyclone. In addition, interaction between a northeastward-drifting trough, the medicane, and the large-scale also permitted the formation of tornadoes within thunderstorms generated by the cyclone after making landfall.
Mediterranean tropical-like cyclone | 11–13 Sep 1996
Tropical cyclones are known to form even when normal conditions are not met. For example, cooler air temperatures at a higher altitude (e.g., at the 500 hPa level, or 5.9 km) can lead to tropical cyclogenesis at lower water temperatures, as a certain lapse rate is required to force the atmosphere to be unstable enough for convection. In a moist atmosphere, this lapse rate is 6.5 °C/km, while in an atmosphere with less than 100% relative humidity, the required lapse rate is 9.8 °C/km. At the 500 hPa level, the air temperature averages −7 °C (18 °F) within the tropics, but air in the tropics is normally dry at this height, giving the air room to wet-bulb, or cool as it moistens, to a more favorable temperature that can then support convection.
Sea surface temperature | Tropical cyclones