|Severe cyclonic storm (IMD scale)|
|Category 1 tropical cyclone (SSHWS)|
|Formed||November 28, 2004|
|Dissipated||December 3, 2004|
|Highest winds|| 3-minute sustained:100 km/h (65 mph)|
1-minute sustained:120 km/h (75 mph)
|Lowest pressure||994 hPa (mbar); 29.35 inHg|
|Part of the 2004 North Indian Ocean cyclone season|
Severe Cyclonic Storm Agni was a tropical cyclone of the 2004 North Indian Ocean cyclone season notable for its record proximity to the equator. It was the second North Indian Ocean cyclone to receive a name, after Onil earlier in the year. Agni formed on November 28 well to the southwest of India in the Arabian Sea, and steadily intensified as it tracked northwestward. The Joint Typhoon Warning Center (JTWC) estimated peak 1 minute sustained winds of 120 km/h (75 mph), while the India Meteorological Department (IMD) estimated peak 3 minute sustained winds of 100 km/h (65 mph); the IMD is the official warning center for the north Indian Ocean. After peaking, it weakened due to wind shear, dry air, and cooler waters, and the JTWC issued its final advisory on December 3 as it approached the coast of Somalia. The remnants of Agni moved along the Somalian coastline until dissipating on December 5.
A tropical cyclone is a rapidly rotating storm system characterized by a low-pressure center, a closed low-level atmospheric circulation, strong winds, and a spiral arrangement of thunderstorms that produce heavy rain. Depending on its location and strength, a tropical cyclone is referred to by different names, including hurricane, typhoon, tropical storm, cyclonic storm, tropical depression, and simply cyclone. A hurricane is a tropical cyclone that occurs in the Atlantic Ocean and northeastern Pacific Ocean, and a typhoon occurs in the northwestern Pacific Ocean; in the south Pacific or Indian Ocean, comparable storms are referred to simply as "tropical cyclones" or "severe cyclonic storms".
The 2004 North Indian Ocean cyclone season was the first in which tropical cyclones were officially named in the basin. Cyclone Onil, which struck Pakistan, was named in late September. The final storm, Cyclone Agni, was also named, and crossed into the southern hemisphere shortly before dissipation. This storm became notable during its origins and became one of the storms closest to the equator. The season was fairly active, with ten depressions forming from May to November. The India Meteorological Department designated four of these as cyclonic storms, which have maximum sustained winds of at least 65 km/h (40 mph) averaged over three minutes. The Joint Typhoon Warning Center also issued warnings for five of the storms on an unofficial basis.
An equator of a rotating spheroid is its zeroth circle of latitude (parallel). It is the imaginary line on the spheroid's surface, equidistant from its poles, dividing it into northern and southern hemispheres. In other words, it is the intersection of the spheroid's surface with the plane perpendicular to its axis of rotation and midway between its geographical poles.
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, gradually organizing and prompting the JTWC to issue a Tropical Cyclone Formation Alert (TCFA) on November 22. After passing south of Sri Lanka, it became disorganized and was no longer considered likely to develop into a tropical cyclone. The circulation associated with the system continued westward, reorganizing on November 26 in the Arabian Sea. Despite being located unusually close to the equator, the disturbance maintained convection, or thunderstorms, which was becoming organized around the weak low-level circulation. With low wind shear and diffluence aloft, the JTWC remarked the system had a fair chance of developing.
Colombo is the commercial capital and largest city of Sri Lanka by population. According to the Brookings Institution, Colombo metropolitan area has a population of 5.6 million, and 752,993 in the city proper. It is the financial centre of the island and a popular tourist destination. It is located on the west coast of the island and adjacent to the Greater Colombo area which includes Sri Jayawardenepura Kotte, the legislative capital of Sri Lanka and Dehiwala-Mount Lavinia. Colombo is often referred to as the capital since Sri Jayawardenepura Kotte is within the urban area of, and a suburb of, Colombo. It is also the administrative capital of the Western Province and the district capital of Colombo District. Colombo is a busy and vibrant place with a mixture of modern life and colonial buildings and ruins. It was the legislative capital of Sri Lanka until 1982.
Sri Lanka, officially the Democratic Socialist Republic of Sri Lanka, is an island country in South Asia, located in the Indian Ocean to the southwest of the Bay of Bengal and to the southeast of the Arabian Sea. The island is historically and culturally intertwined with the Indian subcontinent, but is geographically separated from the Indian subcontinent by the Gulf of Mannar and the Palk Strait. The legislative capital, Sri Jayawardenepura Kotte, is a suburb of the commercial capital and largest city, Colombo.
The Bay of Bengal is the northeastern part of the Indian Ocean, bounded on the west and northwest by India on the north by Bangladesh, and on the east by Myanmar and the Andaman Islands of India and Myanmar and the Nicobar Islands of India. Its southern limit is a line between Sri Lanka and the northwesternmost point of Sumatra (Indonesia). It is the largest water region called a bay in the world. There are Countries dependent on the Bay of Bengal in South Asia and Southeast Asia. The Bay of Bengal was also called the Chola Lake.
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. Three hours later, the agency classified the system as Tropical Cyclone 05A about 1300 km (800 mi) southwest of the southern tip of India. In a post-season analysis, the JTWC estimated the cyclone became a tropical storm six hours earlier. At around the same time, the IMD classified it as a "low pressure area... likely to become well marked."
In geography, latitude is a geographic coordinate that specifies the north–south position of a point on the Earth's surface. Latitude is an angle which ranges from 0° at the Equator to 90° at the poles. Lines of constant latitude, or parallels, run east–west as circles parallel to the equator. Latitude is used together with longitude to specify the precise location of features on the surface of the Earth. On its own, the term latitude should be taken to be the geodetic latitude as defined below. Briefly, geodetic latitude at a point is the angle formed by the vector perpendicular to the ellipsoidal surface from that point, and the equatorial plane. Also defined are six auxiliary latitudes which are used in special applications.
An anticyclone is a weather phenomenon defined by the United States National Weather Service's glossary as "a large-scale circulation of winds around a central region of high atmospheric pressure, clockwise in the Northern Hemisphere, counterclockwise in the Southern Hemisphere". Effects of surface-based anticyclones include clearing skies as well as cooler, drier air. Fog can also form overnight within a region of higher pressure. Mid-tropospheric systems, such as the subtropical ridge, deflect tropical cyclones around their periphery and cause a temperature inversion inhibiting free convection near their center, building up surface-based haze under their base. Anticyclones aloft can form within warm core lows such as tropical cyclones, due to descending cool air from the backside of upper troughs such as polar highs, or from large scale sinking such as the subtropical ridge. The evolution of an anticyclone depends on a few variables such as its size, intensity, moist-convection, Coriolis force etc.
In continuum mechanics, the vorticity is a pseudovector field that describes the local spinning motion of a continuum near some point, as would be seen by an observer located at that point and traveling along with the flow.
Upon being classified, the tropical cyclone was moving northwestward under the influence of a ridge over India. Its outflow to the north and south became better defined, although its proximity to the equator limited its southerly outflow somewhat due to wind shear. 29, the IMD classified the system as a depression, and throughout the day it rapidly intensified to become a cyclonic storm; a cyclonic storm is a tropical cyclone with at least 65 km/h (40 mph) winds sustained for 3 minutes. Around that time, the JTWC assessed the cyclone as reaching peak winds of 120 km/h (75 mph), sustained for 1 minute, along with gusts to 150 km/h (90 mph). Late on November 29, the cyclone weakened slightly, only to regain its peak intensity by November 30; at that time, it developed a banding eye, and was located about 1500 km (900 mi) southeast of the coast of Somalia. At 1200 UTC on November 30, the IMD issued its first complete advisory on the cyclone, naming it Severe Cyclonic Storm Agni and estimating peak winds at 100 km/h (65 mph); the agency predicted the storm would continue northwestward and strengthen slightly before weakening. At its peak, the cyclone had a barometric pressure of 985 mbar.Early on November
Outflow, in meteorology, is air that flows outwards from a storm system. It is associated with ridging, or anticyclonic flow. In the low levels of the troposphere, outflow radiates from thunderstorms in the form of a wedge of rain-cooled air, which is visible as a thin rope-like cloud on weather satellite imagery or a fine line on weather radar imagery. Low-level outflow boundaries can disrupt the center of small tropical cyclones. However, outflow aloft is essential for the strengthening of a tropical cyclone. If this outflow is undercut, the tropical cyclone weakens. If two tropical cyclones are in proximity, the upper level outflow from the system to the west can limit the development of the system to the east.
Wind shear, sometimes referred to as wind gradient, is a difference in wind speed or direction over a relatively short distance in the atmosphere. Atmospheric wind shear is normally described as either vertical or horizontal wind shear. Vertical wind shear is a change in wind speed or direction with change in altitude. Horizontal wind shear is a change in wind speed with change in lateral position for a given altitude.
The maximum sustained wind associated with a tropical cyclone is a common indicator of the intensity of the storm. Within a mature tropical cyclone, it is found within the eyewall at a distance defined as the radius of maximum wind, or RMW. Unlike gusts, the value of these winds are determined via their sampling and averaging the sampled results over a period of time. Wind measuring has been standardized globally to reflect the winds at 10 metres (33 ft) above the Earth's surface, and the maximum sustained wind represents the highest average wind over either a one-minute (US) or ten-minute time span, anywhere within the tropical cyclone. Surface winds are highly variable due to friction between the atmosphere and the Earth's surface, as well as near hills and mountains over land.
After reaching peak intensity, an increase in wind shear caused the eye to disappear, 1, the IMD estimated Agni weakened to cyclonic storm status, around which time the center became exposed from the convection. The cyclone continued its steady weakening continued due to the wind shear, the presence of dry air, and cooler water temperatures, and by December 2, the IMD downgraded Agni to depression status, which was its final warning on the system. As it approached the coast of Somalia, it turned westward due to the building of a ridge over Saudi Arabia. Despite unfavorable conditions, thunderstorms briefly reformed over the circulation, which allowed the storm to maintain its intensity. By late on December 3, Agni weakened to below tropical storm status, and the JTWC issued its final warning while the storm was about 450 km (275 mi) south-southeast of Cape Guardafui—the easternmost point of the Horn of Africa. The circulation became difficult to locate by early on December 4, by which time the system had little remaining convection. It turned southwestward and later to the south, moving ashore on eastern Somalia before dissipating on December 5 near Ceel Huur over water.and the convection decreased significantly. On December
Sea surface temperature (SST) is the water temperature close to the ocean's surface. The exact meaning of surface varies according to the measurement method used, but it is between 1 millimetre (0.04 in) and 20 metres (70 ft) below the sea surface. Air masses in the Earth's atmosphere are highly modified by sea surface temperatures within a short distance of the shore. Localized areas of heavy snow can form in bands downwind of warm water bodies within an otherwise cold air mass. Warm sea surface temperatures are known to be a cause of tropical cyclogenesis over the Earth's oceans. Tropical cyclones can also cause a cool wake, due to turbulent mixing of the upper 30 metres (100 ft) of the ocean. SST changes diurnally, like the air above it, but to a lesser degree. There is less SST variation on breezy days than on calm days. In addition, ocean currents such as the Atlantic Multidecadal Oscillation (AMO), can effect SST's on multi-decadal time scales, a major impact results from the global thermohaline circulation, which affects average SST significantly throughout most of the world's oceans.
Saudi Arabia, officially the Kingdom of Saudi Arabia, is a country in Western Asia constituting the bulk of the Arabian Peninsula. With a land area of approximately 2,150,000 km2 (830,000 sq mi), Saudi Arabia is geographically the largest sovereign state in the Middle East, the second-largest in the Arab world, the fifth-largest in Asia, and the 12th-largest in the world. Saudi Arabia is bordered by Jordan and Iraq to the north, Kuwait to the northeast, Qatar, Bahrain, and the United Arab Emirates to the east, Oman to the southeast and Yemen to the south; it is separated from Israel and Egypt by the Gulf of Aqaba. It is the only nation with both a Red Sea coast and a Persian Gulf coast, and most of its terrain consists of arid desert, lowland and mountains. As of October 2018, the Saudi economy was the largest in the Middle East and the 18th largest in the world. Saudi Arabia also enjoys one of the world's youngest populations; 50% of its 33.4 million people are under 25 years old.
Cape Guardafui, also known historically as Aromata promontorium, is a headland in the autonomous Puntland region in Somalia. Coextensive with Puntland's Gardafuul administrative province, it forms the geographical apex of the Horn of Africa. Its shore at 51°27'52"E is the second easternmost point on mainland Africa after Ras Hafun. Its adjacent locality is called Ras Asir. The offshore oceanic strait Guardafui Channel is named after it.
According to RSMC New Delhi, Cyclone Agni developed into a depression at 1.5° N, which is the same latitude as where according to RSMC Tokyo, Tropical Storm Vamei formed during December 2001. However, according to RSMC La Reunion, the precursor low to Cyclone Agni briefly moved into the Southern Hemisphere and kept its anticyclonic counter-clockwise circulation.
Tropical Storm Vamei was a Pacific tropical cyclone that formed closer to the equator than any other tropical cyclone on record. The last storm of the 2001 Pacific typhoon season, Vamei developed on December 26 at 1.4° N in the South China Sea. It strengthened quickly and made landfall along extreme southeastern Peninsular Malaysia. Vamei rapidly weakened into a remnant low over Sumatra on December 28, and the remnants eventually re-organized in the North Indian Ocean. Afterward, the storm encountered strong wind shear once again, and dissipated on January 1, 2002.
Agni was the second storm in the north Indian Ocean to receive a name, after the IMD began tropical cyclone naming in the middle of 2004.
Since the cyclone was weak when it moved over Somalia, no casualties or significant damage was reported.
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