2020–21 South-West Indian Ocean cyclone season
The 2020–21 South-West Indian Ocean cyclone season was an above-average season which produced 12 named storms, with 7 strengthening into tropical cyclones. The season started with the formation of Cyclone Alicia in the extreme northeast section of the basin on 12 November 2020, just before the official start of the season, which marked the third season in a row in which a tropical cyclone formed before the official start of the season. It officially began on 15 November 2020, and ended with the dissipation of Cyclone Jobo on 24 April, 6 days before the official end on 30 April 2021, with the exception of Mauritius and the Seychelles, which officially ended on 15 May 2021. These dates conventionally delimit the period of each year when most tropical and subtropical cyclones form in the basin, which is west of 90°E and south of the Equator. Tropical and subtropical cyclones in this basin are monitored by the Regional Specialised Meteorological Centre in Réunion and unofficially by the Joint Typhoon Warning Center.
The season was an active season with several notable storms. At the beginning of the season in December, Tropical Storm Chalane hit Mozambique, followed by the stronger and more damaging Cyclone Eloise less than a month later. Both storms caused 34 fatalities and about $10 million in damage. Afterward, Cyclone Faraji formed, strengthening into a very intense tropical cyclone, marking the second season in a row to feature a storm of the type, staying well away from land in its passage. Cyclone Guambe formed as Faraji was weakening, hitting Mozambique as a subtropical system, the third and final occurrence for the country during the season. Toward the end of the season, Cyclone Jobo formed and impacted Seychelles and brought very minor impacts to Tanzania, becoming the first cyclone to affect the latter country in some form since a tropical cyclone in 1952 despite being a remnant low at the time.
Seasonal summary
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On 12 November, Alicia formed on the extreme northeast section of the basin. This formation marked the third season in a row in which a tropical cyclone developed before the official start of the season. Alicia strengthened into a tropical cyclone on 15 November, rapidly weakened due to the vertical wind shear and cool waters, and dissipated on 17 November. On 14 November, another tropical disturbance formed off the coast of Madagascar; however, on 16 November the system failed to organize due to unfavourable vertical wind shear according to JTWC. It rapidly weakened and dissipated the next day. The basin remained quiet until, on 30 November, a tropical low crossed over from the Australian region. It strengthened into a moderate tropical storm, then to a severe tropical storm, and was named Bongoyo. Two additional lows formed, one formed but exited the basin on 20 December and another Zone of Disturbed Weather formed near Diego Garcia, which strengthened to Severe Tropical Storm Chalane, which made landfall on Madagascar and Mozambique, the first tropical cyclone for this season to make landfall. The same Zone of Disturbed Weather which exited on 20 December, again re-entered on 28 December, following with another Zone of Disturbed Weather, designated 06.
On 1 January, 06 intensified into Tropical Storm Danilo. It became the second longest system and dissipated on 12 January. On 15 January, a new disturbance which became depression formed which later became Cyclone Eloise and made two landfalls over Madagascar and Mozambique with second landfall being more catastrophic and brought widespread damages over African nations killing 16 people. On 17 January, Joshua entered the South-West Indian Ocean as a moderate tropical storm; however, it dissipated on 19 January as it entered an area of dry air and high vertical wind shear. On 27 January, Tropical Low 10U entered from the Australian region where it was redesignated as Tropical Depression 09. On 5 February, a tropical depression formed and intensified into Cyclone Faraji, which further became into an intense tropical cyclone, and later a very intense tropical cyclone becoming both the first intense tropical cyclone and the first very intense tropical cyclone of the season. After Faraji, Guambe formed and peaked as a Category 2 tropical cyclone. At the end of February, Marian from the Australian region briefly entered the basin. On 2 March, two tropical depressions formed that were later named Habana and Iman. Iman dissipated quickly, but Habana strengthened into an intense tropical cyclone and stayed active for two weeks. After Habana was a depression that formed on 25 March, but dissipated after three days. Another period of inactivity then ensued, until a zone of disturbed weather formed on 18 April. It was later named Jobo.
Systems
Tropical Cyclone Alicia
On 12 November, Météo-France La Réunion also began tracking a tropical disturbance as it moved slowly westwards over the central Indian Ocean. Later that day, the JTWC issued a Tropical Cyclone Formation Alert. The disturbance slowly consolidated as thunderstorms wrapped around the center of circulation, and it became a tropical depression by 00:00 UTC on 13 November. The depression continued to become more organized over the day with flaring convection over the center, and thus was upgraded to Moderate Tropical Storm Alicia at 18:00 UTC that same day. On 14 November at 06:00 UTC, Alicia strengthened into a severe tropical storm. Alicia generally moved rapidly in a southwesterly direction due to the steering flow of a mid-level subtropical ridge to the storm's southeast. The severe tropical storm intensified into Tropical Cyclone Alicia at 00:00 UTC on 16 November, after very deep convection developed near its center.Soon after Alicia entered a region with high wind shear and cooler waters. Due to these unfavorable conditions, Alicia began to rapidly weaken, weakening to a tropical storm at 12:00 UTC on 16 November. At 09:00 UTC on 17 November, the Joint Typhoon Warning Center issued its final warning on the storm.
Tropical Depression 02
On 12 November, along with the precursor disturbance of Cyclone Alicia, Météo-France La Réunion began to monitor another monsoonal disturbance to the west of Cyclone Alicia's precursor for potential tropical cyclogenesis. By 14 November, an area of disturbed weather had formed but struggled to centralize its thunderstorm activity, despite consolidating a low level circulation. With improvements in further consolidation, the MFR initiated advisories for a tropical depression in the northeast of Madagascar at 18:00 UTC on 15 November. The storm struggled to intensify much due to strong easterly shear from its close proximity to Tropical Cyclone Alicia's outflow, and thus had its thunderstorm activity sheared to its west for most of its lifetime. Due to this, the JTWC cancelled the Tropical Cyclone Formation Alert on 16 November. It rapidly weakened and the last advisory was issued by the MFR on 16 November as well.Severe Tropical Storm Bongoyo
During 30 November, Tropical Low 01U moved into the basin from the Australian region, where it was classified as a Zone of Disturbed Weather by RSMC La Réunion. Early on 4 December, the JTWC issued a Tropical Cyclone Formation Alert on the system. After meandering slowly to the west and northwest for several days with little change in strength, the system began to take a more southerly track and at 06:00 UTC on 6 December was upgraded to Tropical Disturbance 03 by MFR as the low level circulation became tighter and convection consolidated near the center. On 7 December, the disturbance intensified into Moderate Tropical Storm Bongoyo as an ASCAT pass revealed gale-force winds on the southern half of the circulation. At this time, the JTWC cited a favorable environment for further intensification as Bongoyo headed southwest. While Bongoyo gained a distinct mid-level eye and strong bursts of convection were maintained near the center as the storm further strengthened to severe tropical storm status at 00:00 UTC on 8 December.However, Bongoyo's intensification trend was halted as the impacts of strengthening vertical wind shear caused the eyewall to become eroded later into the day. Bongoyo maintained its strength, although the overall structure of the storm became increasingly vertically tilted. On 18:00 UTC on 9 December, Bongoyo finally weakened back down to a moderate tropical storm after maintaining its strength for over a day while convection became sheared away from the circulation. Bongoyo soon began its westward turn on 10 December as it began to ride along the southern edge of a subtropical ridge, and it became a remnant low early on 11 December as all convection sheared away from the low level circulation, thus the last advisory was issued by both MFR and the JTWC.