Intense Tropical Cyclone Berguitta was a strong tropical cyclone that caused flooding in Mauritius and Réunion in January 2018. The third tropical system and first intense tropical cyclone of the 2017–18 South-West Indian Ocean cyclone season, Berguitta originated from an area of scattered thunderstorms southwest of the Chagos Archipelago on 10 January. It slowly organised as it moved southwards, and became a tropical storm as it turned west on 13 January. Berguitta then rapidly intensified to achieve its peak intensity on 15 January while stalling north of Rodrigues. At the time, the cyclone possessed 10-minute sustained winds of , 1-minute sustained winds of , and a minimum central pressure of . Berguitta weakened as it moved slowly west-southwestwards on 16 January, and the cyclone degraded to a tropical storm by 17 January. It accelerated southwestwards over Mauritius and Réunion on 18 January, before degenerating to a post-tropical cyclone the next day. The remnants of Berguitta transitioned into an extratropical cyclone and dissipated over the Indian Ocean on 24 January.
In Mauritius, Berguitta brought heavy rains and gusty winds to Rodrigues from 13 to 15 January. The island experienced a quarter of its average annual rainfall during those three days, resulting in widespread floods, especially in coastal areas. The island's airport was closed for nearly six days, stranding several Mauritians and tourists. Berguitta affected Mauritius's main island on 17 and 18 January, passing just south of the coast. Two days of continuous heavy rain caused severe floods that damaged buildings and at least three‑quarters of the island's crops. A total of 6,800 households lost power after fallen trees damaged power lines, while water supplies to the capital Port Louis were disrupted. Two people were killed on Mauritius: one in a car crash and the other after a fall from a ladder. After the storm, the government gave payouts to 13,000 affected residents, but the small size of the payments and delays in giving them out led to protests. More demonstrations ensued when families were evicted from evacuation centres. Economic losses in Mauritius were estimated at ₨ 2 billion (US$ million).
Réunion was impacted by rain and wind mostly on 18 January. The southern part of the island was particularly hard-hit by floods and landslides. Several rainfall records set by previous cyclones were broken, particularly at Grande Coude, which experienced of rain in eight days, including in 24 hours. Widespread rain-induced flooding caused extensive damage to road infrastructure and agriculture. One person went missing after being swept away by floodwaters. Damage to the power grid left nearly 100,000 customers without electricity, while water supplies were interrupted in several communes. Economic losses in Réunion were estimated at €41 million (US$ million), including €16.7 million (US$ million) of agricultural damage. The town of Cilaos was especially affected after the only road linking it to the island's ports was blocked repeatedly by landslides, severely disrupting economic activity. After Berguitta passed, the government invested several million euros into reconstruction, financial aid, and improving road infrastructure. However, recovery was interrupted by cyclones Dumazile and Fakir in March and April, respectively.
Meteorological history
A zone of disturbed weather formed within the monsoon trough southwest of the Chagos Archipelago on 10 January. As the remnants of nearby cyclones Ava and Irving moved south of the Tropic of Capricorn, the surrounding environment became generally conducive to tropical cyclogenesis, with increased convergence of surface air flows and reduced easterly wind shear. Consequently, the disturbance's center of circulation became better defined as it moved south-southwest. At 12:00 UTC on 11 January, Météo-France La Réunion (MFR)—the Regional Specialised Meteorological Centre for the South-West Indian Ocean—classified the system as a tropical disturbance, the third of the 2017–18 South-West Indian Ocean cyclone season. At the same time, the Joint Typhoon Warning Center (JTWC) identified the system as a tropical depression. An intrusion of dry air on the system's western flank slowed development overnight from 11 to 12 January, before a large burst of thunderstorm activity over the system's center allowed it to consolidate further. The MFR classified the system as a tropical depression at 00:00 UTC on 13 January, then upgraded it further to Moderate Tropical Storm Berguitta six hours later.
Berguitta slowly strengthened on 13 and 14 January as it began to develop a central dense overcast. During that time, a ridge strengthening south of Madagascar caused the storm to turn west then northwest while decelerating. Rapid development began by 15 January while Berguitta became nearly stationary, with the MFR and the JTWC both noting the system to have reached tropical cyclone intensity early that day. Amid high oceanic heat content and low vertical wind shear, an eye quickly formed within the small system. Berguitta reached its maximum strength at 12:00 UTC on 15 January, with the MFR estimating 10-minute sustained winds of , gusts reaching , and a central pressure of . This made Berguitta the season's first intense tropical cyclone on the MFR's scale. Simultaneously, the JTWC estimated peak 1-minute sustained winds of . The cyclone's intensity levelled off thereafter, with little further change in the cloud pattern noted on satellite imagery. Berguitta started to drift west-southwestwards later on 15 January as the aforementioned ridge steering the cyclone started weakening.
Pronounced weakening commenced on 16 January, caused by dry air in Berguitta's northwest quadrant entraining into its circulation and eroding the eastern eyewall. The eye collapsed as the central dense overcast warmed and lost symmetry, leading the MFR to declare Berguitta had degraded to a severe tropical storm at 18:00 UTC. On 17 January, a new ridge developing to Berguitta's east began to steer the system southwest, while causing an increase in northeasterly wind shear. Consequently, further slow weakening occurred, and the MFR assessed that Berguitta's winds bottomed out at as it moved through the Mascarene Islands. For the next day or two, Berguitta's structure and intensity remained relatively unchanged, with scatterometer data indicating winds stayed between . Afterwards, as Berguitta tracked further south, decreasing oceanic heat content caused the cyclone's cloud pattern to lose organisation. The MFR declared the system post-tropical at 18:00 UTC on 19 January as it began accelerating southwards, pulled by an upper-level trough to its southeast. Thunderstorm activity became increasingly limited on 20 January, and the JTWC assessed that Berguitta had transitioned to an extratropical cyclone by 18:00 UTC. The remnants of Berguitta decelerated and turned east-southeast over the next few days while maintaining gale-force winds, even deepening slightly on 21 January. The system soon resumed weakening, however, and was last noted by the MFR near on 24 January.
Effects in Mauritius Rodrigues As Berguitta developed north of Rodrigues, a Class I cyclone warning was issued for the island on 13 January. This was upgraded to a Class II cyclone warning on 14 January as Berguitta strengthened and moved closer to Rodrigues. From 13 to 15 January, Rodrigues experienced gusty winds and heavy rain. A wind gust was recorded in Patate-Théophile on Rodrigues's east coast, and a gust to was observed in Pointe-Canon along the island's north coast. The island received a quarter of its average annual rainfall in those three days, with a peak rainfall total of in Citronelle. A total of 25 people on the island sought shelter in evacuation centres. Coastal roads were inundated and made impassable. Firefighters responded to more than 40 incidents, most of which were flood-related, and the Special Mobile Force was deployed to cut down three trees that collapsed onto electrical cables. The adverse weather caused Sir Gaëtan Duval Airport in Plaine-Corail to close from 13 January, leading Air Mauritius to cancel flights to the island. This left 50 Mauritians and tourists stranded. All cyclone warnings in Rodrigues were lifted on 15 January as Berguitta moved away from the island, though torrential rain continued to affect Rodrigues until 17 January. Residents of Rodrigues were given a day off from work by the local government on 16 January, as some obstructed roads had yet to be cleared. Sir Gaëtan Duval Airport eventually reopened in the evening of 18 January, allowing those stranded to leave the island.
Mauritius Island
Preparations and impact While Berguitta moved away from Rodrigues, it turned towards the main island of Mauritius, leading authorities to issue a Class I cyclone warning for the island on the afternoon of 15 January. This was raised to a Class II cyclone warning on the morning of 16 January, and further upgraded to Class III just 24 hours later. The MFR originally expected the centre of Berguitta to pass directly over the island; the cyclone eventually passed off the coast of Souillac. Berguitta's predicted trajectory and intensity generated comparisons to 1994's Cyclone Hollanda and 2002's Cyclone Dina. Schools were closed from the morning of 16 January, and the National Disaster Risk Reduction and Management Centre announced that workplaces would be closed and workers placed on mandatory leave beginning on 17 January. Sir Seewoosagur Ramgoolam International Airport was closed until further notice on the morning of 17 January, leading Air Mauritius to cancel its flights and other international airlines to reschedule theirs. The State Bank of Mauritius disabled its automated teller machines from the evening of 16 January. The Judiciary of Mauritius postponed 2,512 trials scheduled for 17 and 18 January. Authorities opened 172 evacuation centres across the island; a total of 4,043 people sought shelter in 79 of these centres on 17 and 18 January. Demand was greatest in the capital Port Louis, where an additional centre had to be set up on the spot. At these centres, evacuees were provided with water, hot meals, snacks, and mattresses.