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1998–99 South-West Indian Ocean cyclone season
The 1998–99 South-West Indian Ocean cyclone season was a quiet season that had the fourth-lowest number of days with tropical storm or tropical cyclone activity. Most of the storms formed either in the Mozambique Channel or in the far eastern portion of the basin, with five storms crossing from the adjacent Australian basin east of 90° E. As a result, few storms impacted Madagascar, and none made landfall on the African continent. Throughout most of the season, there was below-normal sea surface temperatures in the Indian Ocean east of Madagascar. In February, typically the peak in activity, Réunion island recorded its highest average monthly pressure since 1953. Due to generally unfavorable conditions, there were only six tropical storms tracked by the Météo-France office (MFR) on Réunion. There were only two tropical cyclones – a storm with winds of at least 120 km/h (75 mph).
Activity began late, with the first tropical storm – Alda – forming on January 16, the third latest ever recorded at the time. Alda formed in the Mozambique Channel, which was one of few favorable areas for tropical cyclogenesis in the season. It brought rainfall to southwestern Madagascar that alleviated previously dry conditions. The next five tropical storms either originated or crossed into the adjacent Australian basin, where storms were monitored by the Bureau of Meteorology (BoM). Both Tropical Storm Chikita and Tropical Cyclone Davina brought beneficial rainfall to the Mascarene Islands. The latter storm caused two drowning deaths on Réunion and caused some crop damage. The strongest storm – Evrina – peaked as a strong cyclone in the Australian but weakened upon crossing 90°E, with 10-minute maximum sustained winds of 175 km/h (110 mph) in the basin. The final storm was unnamed, crossing from the Australian basin on April 21 as a minimal tropical storm before quickly dissipating. There were also several tropical disturbances or depressions, many short-lived. The first of these formed on September 3 in the northeastern portion of the basin, and there was a tropical depression in February in the Mozambique Channel that approached tropical storm status.
==Season summary==
The Météo-France office (MFR) on Réunion island issued warnings in tropical cyclones within the basin during the season. The agency estimated intensity through the Dvorak technique,〔 and warned on tropical cyclones in the region from the coast of Africa to 90° E, south of the equator. The Joint Typhoon Warning Center – a joint United States Navy – United States Air Force task force – also issued tropical cyclone warnings for the region. Wind estimates from Météo-France and most other basins throughout the world are sustained over 10 minutes, while estimates from the United States-based Joint Typhoon Warning Center are sustained over 1 minute. 10 minute winds are about 1.14 times the amount of 1 minute winds. Most storms formed and dissipated within the tropics, with the exception of Severe Tropical Storm Alda.〔
During the season, atmospheric conditions shifted from El Niño to La Niña, but despite the shift, the season was similarly inactive as its predecessor. In general, sea surface temperatures were below normal, and atmospheric pressures were above normal, both unfavorable for tropical cyclogenesis. In the month of February, on average the peak time for activity, there was a general lack of convection, or thunderstorms, east of Madagascar. The average monthly pressure on Réunion was the highest since reliable records began in 1953. The low number of storms occurred despite an otherwise active cyclone year in the southern hemisphere. In its summary of the season, the MFR described the lack of activity as "rare and remarkable", possibly related to a Walker circulation. The agency monitored 14 tropical disturbances, of which only eight were tropical depressions for at least 24 hours. Six of these intensified into tropical storms, three less than the average of nine, of which only two attained tropical cyclone status, or half the average. There were 28 days in which there was storm or tropical cyclone activity, less than the average of 42 and at the time the fourth lowest since reliable record-keeping began in 1967 with the advent of satellite imagery. The only seasons with a lower number of storm days were 1982–83, 1986–87, and 1997–98.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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