The 1999–2000 South-West Indian Ocean tropical cyclone season was the first on record in which two storms – Leon–Eline and Hudah – struck Mozambique at tropical cyclone intensity, or with maximum sustained winds of at least . The most notable storm of the season was Eline, which was the third longest-lasting storm on record in the basin. It lasted for 29 days while traversing the southern Indian Ocean, making the strongest landfall in decades along eastern Madagascar in late February. The storm was the first in a series of three storms that struck the country in early 2000, along with Gloria in March and Hudah in April. Collectively, the three storms killed at least 316 people. The season started on November 1, 1999, and ended for most of the basin on April 30, 2000; for Mauritius and the Seychelles, the season continued until May 15. These dates conventionally delimit the period of each year when most tropical cyclones form in the basin.
Despite the destructive nature of the season, it began later than usual. Cyclone Astride originated toward the end of December, bringing rainfall and gusty winds to northern Madagascar while in the region. In January, Cyclones Babiola and Connie both formed east of Madagascar and took southerly tracks. Connie passed near Réunion island, producing of rainfall in the mountainous peaks and killing two people. Eline, the longest lasting storm of the season, struck Mozambique while the country was experiencing its worst flooding in 50 years, collectively causing around 700 deaths and about $500 million in damage. The storm also killed 12 people in Zimbabwe and 21 in South Africa. Just two weeks after Eline struck Madagascar, Tropical Storm Gloria affected the same general region, bringing additional deaths and damage. Cyclone Hudah in April was the strongest storm of the season, reaching peak 10‑minute winds of . It caused three deaths in Mozambique, although its effects were worse in Madagascar, where there were 111 deaths. The final storm of the season was Tropical Storm Innocente, which dissipated on April 24. In addition to the named storms, there were four unnamed tropical disturbances or storms, as well as one subtropical cyclone that formed in the southern Mozambique Channel.
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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, which utilized the continuous satellite imagery in the basin since May 1998. Wind estimates were sustained over 10 minutes, to be converted to 1‑minute winds by dividing by 0.88, as compared to a divisor of 0.80 in previous years. Warnings on tropical cyclones in the region were 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. Beginning this season, the MFR changed their method for labeling tropical disturbances, classifying them sequentially by number. In previous years, the agency labeled disturbances by letter and number of the subsequent unnamed storm.
The season began later than usual, the third consecutive one to do so. There were no indications of tropical cyclogenesis before the middle of December, putting the season among the latest 20% since 1967 in terms of seasons' first storms. On December 26, the MFR utilized the QuikSCAT satellite for the first time in the basin to assess a storm's intensity. During the season, 14 tropical disturbances formed, which is near average, and they tended to last longer than normal. Eleven of these disturbances became tropical depressions, of which nine attained gale force winds and were named. In addition, four storms reached tropical cyclone intensity, or 10‑minute sustained winds of . The 9 named storms and 4 tropical cyclones is also the basin average for each category in a given year. There were 61 days in which a storm was active, greater than the median of 48 and more than double than the previous season. In general, storms formed south of 10° S, with the exception of the first storm Astride, and most storms generally tracked east to west due to a strong ridge east of Madagascar.
Systems
Severe Tropical Storm Astride
On December 23, a circulation with accompanying convection became evident about southeast of Diego Garcia, becoming a tropical disturbance. While moving to the south, the thunderstorms organized more, aided by low wind shear, good outflow, warm waters, and its position beneath an anticyclone. Curving west-southwestward due to a ridge to the south, the system intensified into a tropical depression and later Tropical Storm Astride on December 25. That day, the JTWC classified the system as Tropical Cyclone 03S. The storm developed a large area of convection, prompting the MFR to upgrade it to a severe tropical storm on December 26, estimating 10‑minute winds of . On December 27, the JTWC upgraded Astride to the equivalent of a minimal hurricane due to the appearance of an eye feature, estimating 1‑minute winds of . Later that day, the storm weakened unexpectedly, perhaps related to wind shear from a trough to the south. The convection deteriorated markedly, and the weakening storm turned more to the west-northwest on December 29 due to a weaker ridge. Convection reorganized slightly, although it was dislocated from the center. Early on December 30, the storm passed about northeast of Tromelin Island. Curving back to the west, Astride struck northeastern Madagascar between Vohemar and Antsiranana on December 31 as a minimal tropical storm. It emerged into the Mozambique Channel as a tropical depression, and despite forecasts to the contrary, it reintensified into a tropical storm before passing near Mayotte on January 2. Early the next day, Astride weakened back to tropical depression status before moving ashore eastern Mozambique near Pemba, dissipating soon after.
On Tromelin, Astride brought strong winds, including 10‑minute sustained winds of and gusts to . No damage was reported in Madagascar during the storm's passage there. When Astride passed just south of Mayotte, it brought gusts to , strong enough to knock over some banana trees and to destroy a stone house. The storm also dropped of rainfall over 24 hours, including in one hour. Heavy rainfall accompanied Astride's final landfall, penetrating as far inland as Malawi.
Tropical Cyclone Babiola
Toward the beginning of January, the Intertropical Convergence Zone (ITCZ) remained active across much of the basin, with low pressure and widespread thunderstorms. One such area persisted southeast of Diego Garcia and organized sufficiently to be classified as a tropical disturbance on January 3. That day, the JTWC issued the first of three Tropical Cyclone Formation Alerts, noting the increase in convection. The system moved to the northeast along the southeastern edge of a ridge near the equator, but turned back to the southwest on January 5. That day, convection increased over the center, after having previously been dislocated due to wind shear. Late on January 5, the JTWC initiated advisories on Tropical Cyclone 02S, and on the next day, the MFR upgraded the system to Tropical Storm Babiola. The storm accelerated to the southwest and continued to intensity. An irregular eye formed on January 8, prompting the MFR to upgrade Babiola to tropical cyclone status. The outflow and the eye became more pronounced after further strengthening, and the cyclone attained peak 10‑minute winds of on January 9. The JTWC, by contrast, estimated peak 1‑minute winds of .
Around the time of peak intensity, Babiola began turning more to the south due to an approaching trough. Late on January 9, the cyclone passed about east of Rodrigues. Increased shear weakened the eyewall and convection, and Babiola weakened below cyclone status on January 11. Early the next day, the JTWC discontinued advisories as the storm was beginning to become extratropical. The MFR followed suit later on January 12, although the agency continued to track Babiola. The storm shifted south-southwestward on January 13 before resuming its southeast trajectory, influenced by a ridge to the south. On January 14, the remnants of Babiola passed just west of Île Amsterdam, where gusts reached . Later that day, the storm merged with the trough that had originally turned it to the southeast.
Intense Tropical Cyclone Connie
An area of thunderstorms formed on January 22 east of the northern tip of Madagascar, organizing into a tropical disturbance three days later. By late on January 25, the MFR upgraded the system to Tropical Storm Connie, and on the same day the JTWC initiated advisories on the storm as Tropical Cyclone 08S. With favorable conditions, Connie gradually organized while initially stationary, later beginning a steady southeast motion on January 26. The JTWC upgraded the storm to the equivalent of a minimal hurricane on January 27, around the same time that the MFR upgraded Connie to tropical cyclone status. The storm's eye became well-defined as the winds increased, and the MFR estimated peak 10‑minute winds of on January 28; on the same day, the JTWC estimated peak 1‑minute winds of . Increased shear weakened the storm as it curved southwestward, and late on January 29 Connie passed about northwest of Réunion. The storm turned to the southeast again and became extratropical on February 1, dissipating the next day.
While passing northwest of Mauritius, the outer fringes of Connie brought heavy rains peaking at over the span of six days, or equivalent to a month's worth of precipitation. These rains helped relieve extreme drought conditions. The storm also produced gusts of , and one person died after falling off his roof. The storm also brought heavy rainfall to Réunion, totaling , of which occurred in over 24 hours. Wind gusts there reached in Peite France. Many roads across the island were damaged, and about 40,000 people lost power, while more than 100 homes were destroyed. Two persons were killed, and 600 people were left homeless. Although the agriculture sector suffered the most significant damages, overall damage was minor.
Moderate Tropical Storm Damienne
The same monsoon trough that spawned Connie also produced an area of convection southeast of Diego Garcia on January 28. The circulation slowly organized, and the MFR classified it as a tropical disturbance on January 30. A nearby trough steered the system southeastward initially and later to the southwest. On January 31, the system became a tropical depression, and later Moderate Tropical Storm Damienne the next day, reaching peak winds of . Also on February 1, the JTWC initiated warnings on Tropical Cyclone 10S, which estimated 1‑minute winds of . Increased wind shear removed the convection on February 2, causing marked weakening, and prompting the JTWC to discontinue advisories that day. This was despite forecasts of strengthening to near tropical cyclone status. As a weak tropical disturbance, Damienne turned to a rapid westward motion, passing north of Rodrigues and Tromelin. The circulation dissipated on February 7 off the northeast coast of Madagascar.
Intense Tropical Cyclone Leon–Eline