2012–13 South-West Indian Ocean cyclone season
The 2012–13 South-West Indian Ocean cyclone season was a slightly above average event in tropical cyclone formation in the Southern hemisphere tropical cyclone year starting on July 1, 2012, and ending on June 30, 2013. 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. The first tropical disturbance of the season developed on October 12 and rapidly developed into the earliest known intense tropical cyclone on record during October 14.
Seasonal summary
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The first tropical disturbance of the season developed on October 12 and gradually intensified to become the earliest known intense tropical cyclone on record on October 14.
Systems
Intense Tropical Cyclone Anais
On October 12, 2012, the JTWC issued a Tropical Cyclone Formation Alert on a system near the Chagos Islands. Soon afterwards, RSMC La Réunion designated the system as a tropical disturbance while located roughly to the west of Diego Garcia. That afternoon, the JTWC upgraded the system into a tropical depression, giving it the designation 01S. The next day, RSMC La Réunion reported that the system had intensified into a moderate tropical storm and named it Anais. As the day progressed, Anais began a period of quick intensification—being upgraded into a tropical cyclone by RSMC La Réunion and a category one tropical cyclone by the JTWC. Late on October 15, as it started to weaken, the system's eye started to collapse, but deep convection remained over the low level circulation center, and it was downgraded to a category 1 cyclone by October 16. On October 17, the system weakened into a tropical storm, and the low-level circulation center became totally exposed, with convection being displaced to the south due to moderate vertical wind shear from the north west. As the day progressed, Anais weakened into a tropical depression.On October 14, Anais became the earliest intense tropical cyclone in the South-West Indian Ocean.
Tropical Disturbance 02
On November 8, an area of low pressure formed far northeast of La Réunion. It gradually drifted west and developed a low-level circulation center. On the next day, isolated convection developed around the system with fragmented spiral banding. The low drifted southwest and slightly weakened on November 12. The low-pressure area soon became disorganized and the JTWC stopped tracking it later that day. Early on November 15, the disturbance regained strength and the convective banding around its LLCC improved and JTWC resumed tracking the system. At the same time, RSMC La Réunion upgraded the low-pressure area to a tropical disturbance. The next day, the system lost most of its convection and Météo France stopped tracking the disturbance, reporting that their forecast models showed no chance of the system restrengthening.Severe Tropical Storm Boldwin
On November 23, the system organized under moderate vertical wind shear, and the Météo-France started to track the system as a tropical disturbance By midnight, that day, Météo-France further upgraded the system to a tropical depression. In the early hours of November 24, RSMC La Réunion further upgraded the tropical depression into a Moderate Tropical Storm with Mauritius assigning it the name Boldwin. Later the same day, the JTWC also started tracking the system as Tropical Cyclone 02S with winds equivalent to a tropical storm on the SSHS, while it developed an eye-like feature. During the afternoon, Météo-France further upgraded Boldwin into a Severe Tropical Storm with 10-minute sustained winds reaching. On November 25, the storm encountered strong vertical wind shear and much of its convection got displaced to the southeast, partially exposing the center. That day, Boldwin weakened into a Moderate Tropical Storm. Later that night, Boldwin's LLCC became fully exposed and started weakening rapidly. As a result, the JTWC issued their final advisory on the system. At the same time, Météo-France reported that Boldwin further weakened into a Tropical Depression. Finally, during the early hours of November 26, Météo-France issued their final warning on Boldwin, as it weakened into a remnant low, as moderate vertical wind shear had torn the system apart.Intense Tropical Cyclone Claudia
The disturbance moved south-westwards over the following week, strengthening as wind shear decreased. On 6 December, JTWC issued a TCFA and RSMC La Réunion commenced advisories for a Tropical Disturbance. The disturbance was then located about 900 km SE of Diego Garcia. The next day it was named Moderate Tropical Storm Claudia by NWS Mauritius. On December 8, Cyclone Claudia was in South Indian Ocean and had strengthened rapidly with winds over. On December 10, a well-developed eye was observed, with diameter of approximately 19 km. By December 11, Claudia's eye had dissipated, and the cyclone became more disorganized, with wind shear causing elongation from east to west. Claudia moved into sea surface temperatures below, as a result of the western edge of a high pressure ridge steering the system south. On December 12, high vertical wind shear near 30 knots impacted the northwestern quadrant of the low level circulation center, exposing the center, as it became extratropical over cooler waters. On December 13, the system became fully extratropical, with the low level circulation center becoming fully exposed, and convection displaced far south of the circulation center by strong vertical wind shear.Tropical Cyclone Dumile
On December 28 a low-pressure area continued to organize, with a significant increase in convection, located just to the west of an anticyclone.In Mauritius, the storm produced winds up to that downed trees and power lines. Transportation across the region was several disrupted as public transit was shut down and many roads were blocked by debris. In Cassis, a billboard collapsed and damaged a nearby home. One person was found dead after his body washed ashore in Flic-en-Flac. In addition to winds, the storm brought heavy rains to the region, amounting to in Arnaud. Overall, damage from the storm was fairly limited in Mauritius.
Cyclone Dumile produced strong winds across Réunion Island, peaking at, that downed numerous trees and power lines, leaving approximately 125,000 residents without electricity. Downed wires also led to the death of one person after he tried to remove a live wire from the roof of his home. Additionally 14 people were injured by the storm. Heavy rains also affected much of the island, with falling in Cirad over a 24‑hour span. These rains proved to be mostly beneficial, restoring reservoirs and replenishing rivers, as the island experienced below-average rainfall in the preceding two months. Significant agricultural damage took place on the island, with losses reaching €31 million. Insured losses were estimated at €3.5 million.
Moderate Tropical Storm Emang
By December 28, the JTWC began tracking the system, as it began to make a significant increase in deep convection, with formative convective banding developing around the system. At that time, the disturbance was located west of an upper-level anticyclone and directly beneath a subtropical ridge center, in an area of light vertical wind shear, north-northwest of Learmonth, Australia.On December 30, the low-level circulation center became partially exposed due to moderate to strong easterly moving vertical wind shear, while the western part of the system still had deep, persistent convection.
By January 17, Emang became disorganized and weakened into a small area of flaring convection. The low-level circulation center had become weak and poorly defined, due to moderate vertical wind shear.