The 2013–14 South-West Indian Ocean cyclone season was an above-average event in tropical cyclone formation. The season officially began on July 1, 2013, though the first tropical system designated by Météo-France was a short-lived tropical disturbance that developed on July 8. However, the first named storm was Cyclone Amara in December. Bruce was the first very intense tropical cyclone since Edzani in 2010, which originated from the Australian region. The strongest system of the cyclone season was Hellen, also one of the most intense tropical cyclones over the Mozambique Channel. The season officially ended on June 30, 2014.
Within this basin, tropical and subtropical disturbances are officially monitored by the Regional Specialised Meteorological Centre on Réunion island, while the Mauritius and Madagascar weather services assign names to significant tropical and subtropical disturbances.
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Seasonal summary
Systems Moderate Tropical Storm 01
The predecessor to the season's first designated tropical depression began as an area of persistent convection well removed from any landmasses. The JTWC began issuing products on the storm complex on October 21, noting recent consolidation patterns and its association with an ill-defined low-level circulation centre. Over subsequent hours, the system developed a central region of convection with incipient rainbands. Despite these signs of potential tropical cyclogenesis in the very near future, the storm remained unclassified for several days as it tracked generally towards the west. At 1200 UTC on October 25, however, Météo-France classified the system as a tropical disturbance. Though upper-level atmospheric conditions were rather conducive for continued strengthening, factors including decreasing convergence and marginally sustainable sea surface temperatures were expected to inhibit tropical development, and as such initial forecasts only anticipated minimal and gradual strengthening.
At 0600 UTC on October 26, Météo-France upgraded the system to tropical depression status. Forecasts upon the system's upgrade to tropical depression intensity expected more significant intensification, with the depression expected to peak as a moderate tropical storm. However, the depression peaked in strength later that day with winds of and a minimum pressure of 1000 mbar (hPa; ). This intensity was sustained for several hours before the storm began to slowly weaken early on October 27. During its weakening phase, the depression became elongated and its circulation center became exposed from the rest of the convection, and at 12:00 UTC that day, Météo-France reclassified the storm as a tropical disturbance. In an area no longer sufficient to support strengthening, the disturbance gradually diffused, and six hours later, Météo-France issued their last advisory on the system. The tropical depression was upgraded to Moderate Tropical Storm 01 during post-analysis of the season.
Intense Tropical Cyclone Amara
Amara developed from a disturbance within the monsoon trough on December 14. The following day, the system attained tropical depression status. Despite its ill-defined organization, the depression was able to continue strengthening, reaching moderate tropical storm status on December 16 as it tracked southwest. Situated in a favorable atmospheric environment, a period of rapid intensification ensued after Amara reached tropical cyclone status on December 18. After fluctuating in strength, the cyclone peaked with maximum sustained winds of and a minimum barometric pressure of 933 mbar (hPa; ) on December 21, making it an intense tropical cyclone based on the intensity scale utilized by Météo-France. Shortly after, wind shear strengthened as Amara tracked southeast, resulting in a weakening phase. The shearing effects caused the cyclone to rapidly decay, and by December 23, Amara was determined to have degenerated into a remnant low.
Amara was initially expected to track directly over the island of Rodrigues, prompting widespread precautionary measures and resulting in the issuance of a Class 4 warning – denoting a warning of highest urgency – by the Mauritius Meteorological Services. Though the tropical cyclone eventually passed to the east of the island, Amara was close enough to Rodrigues to severely affect the island. Strong winds, peaking at a measured 152 km/h (94 mph) in Pointe Canon, resulted in widespread infrastructural damage, including the tearing of metal sheeting and uprooting of trees. Widespread power outage cut power to 12,000 homes and shut off communications to and from the island. Heavy rains produced by Amara also triggered flooding in some locations and caused soil erosion.
Very Intense Tropical Cyclone Bruce
On December 16, a complex of disturbed weather near Indonesia was designated as a tropical low by the Australian Bureau of Meteorology. In an area of only moderate inhibiting atmospheric conditions, the low was able to steadily intensify, reaching tropical cyclone status on December 18 as it tracked southwestward. At 21:00 UTC on December 19, Bruce moved into the area of responsibility of Météo-France after crossing 90°E with maximum sustained winds of . Upon passage into the southwest Indian Ocean Bruce already had a well-defined eye and further strengthening was anticipated. Six hours later the storm was upgraded to intense tropical cyclone status. At 1800 UTC that day, Météo-France upgraded the system to very intense tropical cyclone status, the highest rating possible on their tropical cyclone intensity scale. Over the next day, Bruce transiently weakened to intense tropical cyclone status, but later regained the maximum classification at 00:00 UTC on December 22. Consequently, Bruce reached its peak intensity with winds of and a minimum pressure of 920 mbar (hPa; ).
Following peak intensity, Bruce began to steadily weaken as the storm's deep region of convection began to diminish. At 12:00 UTC on December 22, the storm was downgraded back to intense tropical cyclone status for a final time as it was becoming increasingly asymmetric. During the same timeframe Bruce began to curve around the western periphery of a nearby subtropical ridge, redirecting the cyclone's path towards the south. On December 23, the cyclone's eye finally succumbed to cooling sea surface temperatures and Bruce was downgraded to a low-end tropical cyclone by Météo-France. By the end of the day, Bruce was downgraded further to severe tropical storm intensity as the bulk of convection began to shear away from the low-level circulation center. Accelerating southeastwards, Bruce transitioned into an extratropical cyclone on December 24, ceasing Météo-France's monitoring operations.
Intense Tropical Cyclone Bejisa
In late December 2013, computer forecast models began to predict the development and cyclogenesis of a disturbance within the monsoon trough north of Madagascar. At 1800 UTC on December 27, the Joint Typhoon Warning Center (JTWC) noted a discrete area of disturbed weather approximately north-northwest of Réunion that corresponded with model forecasts and had the potential to develop. Accompanied by a low-level circulation center, the monitored storm complex developed rainbands about its southern periphery the following day. At 12:00 UTC on December 28, Météo-France deemed the system sufficiently organized to be considered a tropical disturbance, the fourth system to be given such a classification by the agency that season. Upon its designation, the disturbance was analyzed to have an unusually high barometric pressure, based on nearby weather station observations. Météo-France projected for the system to peak as a tropical cyclone before slightly weakening before impacting the Mascarene Islands.
Tracking southward, the disturbance steadily organized following December 28. As a result of wind shear, the system's low-level circulation centre remained partially exposed, though the shearing conditions were expected to lessen At 00:00 UTC on December 29, the disturbance was upgraded to a tropical depression. At 18:00 UTC that day, the depression intensified to moderate tropical storm intensity, thus receiving the name Bejisa by the Mauritius Meteorological Services. This coincided with the improving satellite appearance of the storm's central dense overcast. Intensification subsequently quickened, and at 06:00 UTC the next day Bejisa was considered to be a severe tropical storm. Concurrently a strengthening ridge in the mid-levels of the troposphere began to steer the storm towards the south-southeast. Following the development of a small pinhole eye, Bejisa was upgraded to tropical cyclone status at 12:00 UTC on December 30, followed by intense tropical cyclone status six hours thereafter. This intensification phase was short-lived, as an eyewall replacement cycle resulted in a slight deterioration and fluctuation of the storm's organization and structure.
Tropical Depression 05
The initial development of the season's fifth tropical depression was quickly paced. The JTWC first began monitoring the system in its advisories at 18:00 UTC on January 7, while the area of disturbed weather was within the Mozambique Channel. By that time, a well-defined low-level circulation center had already developed, and computer models indicated that tropical cyclogenesis was a likely probability due to the storm's expected track within a favorable atmospheric environment. At 12:00 UTC on January 8, Météo-France classified the system as a zone of disturbed weather, though at the time the storm's convective activity was intermittent. Shortly after designation the system developed, albeit shallow, convective banding. At 06:00 UTC the following day, the zone of disturbed weather was upgraded to tropical depression status while just off the west coast of Madagascar.
Forecasts early in the depression's history indicated that heavy rainfall was likely in areas of southwestern Madagascar, though these rains would come during an extended period of abnormally dry weather. As a result, the Madagascar National Bureau for Risk and Disaster Management issued a red alert, signifying imminent heavy rain, for five Malagasy districts and a yellow alert, signifying a threat of heavy rain, in seven districts. In Morondava, 205 people were evacuated to safe havens where authorities provided food.
Intense Tropical Cyclone Colin
A tropical low in the Australian region basin formed on January 6, which was about east-northeast of Christmas Island. Over the next days the system moved rapidly westwards and entered the Southwest Indian Ocean during the morning of January 9. Despite being under significant wind shear, the system managed to organize a low level eye which was detectable in microwave imagery. As a result, the storm was upgraded to moderate tropical storm strength and named Colin the next day. On January 11 shear let up, allowing Colin favourable conditions for strengthening. Tracking southwest, Colin rapidly intensified much faster than initial predictions expected into an intense tropical cyclone during the succeeding 24 hours. Six hours later on January 12, Colin had reached its peak intensity of 185 km/h (115 mph). Just like cyclones Amara and Bruce, Colin had undergone rapid deepening. But by January 13, Colin's eyewall had become severely eroded and the system was downgraded to a severe tropical storm. As it tracked further into cooler waters, the storm weakened to tropical storm strength early on January 14 and made a turn to the southeast. Environmental conditions continued to become unfavourable and the storm transitioned into an extratropical cyclone on January 15.
Moderate Tropical Storm Deliwe