The 2002–03 South-West Indian Ocean cyclone season was one of the longest lasting and the fourth-most active season in the South-West Indian Ocean. Storms during the season impacted the Mascarene Islands, Seychelles, Madagascar, and countries in south-eastern Africa. The season began early when an unnamed tropical storm struck Seychelles in September, becoming the most damaging storm there in 50 years. The next system, Atang, was the first named storm of the season, but was only a tropical depression; it was named due to the threat to an outer island of Mauritius. Atang later struck Tanzania in a climatologically unusual area in November, resulting in unconfirmed deaths of fishermen. The first named storm to reach tropical storm intensity was Boura, which brushed the Mascarene Islands with gusty winds and rainfall. In December, Cyclone Crystal threatened to strike Mauritius but instead veered eastward, and later, Tropical Storm Delfina lasted from late December through early January 2003. Delfina damaged or destroyed thousands of houses in Mozambique and Malawi, killing 54 people.
In January 2003, Severe Tropical Storm Ebula continued the steady activity, forming in the eastern portion of the basin. Later, Tropical Storm Fari crossed southern Madagascar with heavy rains, causing flooding and mudslides that left 3,400 people homeless. In February, there were four simultaneous tropical cyclones in the Indian Ocean, three of which in the basin. Cyclone Gerry formed first and the farthest west, passing just east of Mauritius and killing one person there. Cyclone Hape formed shortly thereafter, and Tropical Storm Isha formed farther east, having originated from the Australian basin. Cyclone Japhet struck southern Mozambique and produced widespread flooding in south-eastern Africa, killing 25 people. In March, Cyclone Kalunde was the strongest storm of the season, reaching 10-minute sustained winds of . It struck Rodrigues while weakening, damaging 1,600 houses and causing an island-wide power outage. About a month later, a subtropical cyclone named Luma intensified south-east of Madagascar and developed an eye. Lastly, Cyclone Manou was only the sixth May tropical cyclones on record, making a rare landfall in south-eastern Madagascar, killing 89 people and destroying thousands of houses.
Season summary
Météo-France's meteorological office in Réunion (MFR) is the official Regional Specialized Meteorological Center for the South-West Indian Ocean, tracking all tropical cyclones from the east coast of Africa to 90° E. At the beginning of the season, the MFR moved the tropical cyclone year from August 1 to July 1. The Joint Typhoon Warning Center (JTWC), which is a joint United States Navy – United States Air Force task force that issues tropical cyclone warnings for the region, also issued advisories for storms during the season.
During the season, MFR issued advisories on 16 systems, of which 13 intensified to reach tropical storm force winds, meaning conditions were generally favorable for tropical cyclogenesis. The 13 systems with tropical storm force winds is only one short of the most such storms since the beginning of satellite-tracking in the 1967–68 season, set in the 1993–94 season. This is four more than the average of nine named storms. In this season, there were 24 days on which tropical cyclones were active, slightly above normal, but only one storm—Kalunde—remained at that intensity for more than three days. By contrast, there were 68 days in which a tropical storm was active in the basin, which is 15 days above normal. The season began early and ended late; only four seasons began earlier and four ended later than this season since the start of satellite-coverage in the basin.
In addition to the named storms and an unnamed tropical storm in September, there was one non-developing tropical depression. On December 25, Tropical Depression 05 developed in the north-eastern portion of the basin. It moved to the south and later south-east, crossing into the Australian region on December 27. A day later, the JTWC issued its last advisory.
Systems
Moderate Tropical Storm 01
In late August, a weak low-level circulation persisted near Diego Garcia. It was associated with a trough near the equator, and initially remained disorganized due to high wind shear. The disturbance was located at a low latitude near the equator, and a ridge extending from the eastern coast of Africa imparted a general west-south-west movement. The system was organized enough to be classified by MFR on September 5 at 3.1° S. Subsequently, the system developed more convection as its circulation became better defined. Operationally, MFR began issuing warnings on September 5 on Tropical Disturbance 01, and the next day upgraded it to a tropical depression. Post analysis from MFR indicated that the system reached peak winds of on September 6, the same day that the Joint Typhoon Warning Center (JTWC) initiated advisories on it as Tropical Cyclone 01S. The storm developed banding features, but the thunderstorms were sheared away from the circulation. On September 7, the storm moved through Seychelles—an island nation in the southern Indian Ocean—before weakening. MFR discontinued advisories on September 8, and the JTWC followed suit the next day.
While moving through Seychelles, the storm produced a microburst that lasted for two hours across several islands, producing wind gusts up to on Praslin. Heavy rainfall affected Praslin, La Digue, and particularly Mahé, which reported in a 24‑hour period. Damage on Mahé was limited to landslides and some flooding. On Praslin, high winds damaged the roofs of over 50 houses and destroyed six homes, while the airport was also damaged. The winds damaged 50 power lines, causing an island-wide power outage. High winds also downed about 30,000 trees, which blocked roads but were quickly removed. Due to widespread tree damage, Cousin Island—a nature preserve—was closed for about two weeks, accounting for about $50,000 (2002 USD, SR250,000 rupees) in damage. Nationwide, the storm left 375 families homeless and damaged crop fields, becoming the most damaging in the country in 50 years.
Tropical Depression Atang
Convection persisted near a broad circulation on November 3 to the west of Diego Garcia. The system moved westward and organized due to generally favorable conditions. MFR classified it as Tropical Disturbance 02 on November 4. Two days later, the agency upgraded it to Tropical Depression 2, and shortly thereafter the JTWC initiated advisories on Tropical Cyclone 02S. At that time, the storm was moving to the south-west toward the Mauritius outer island of Agaléga, developing improved outflow. To emphasize the threat, the Meteorological Service of Mauritius named the system Atang, despite it only being a tropical depression. Late on November 6, JTWC estimated peak winds of , around the same time that Atang began a slow motion to the southwest. The next day, the depression resumed a westward motion and became disorganized, with several circulations, and the JTWC and MFR both discontinued advisories. The remnants of Atang again turned to the south-west and re-intensified, prompting JTWC and MFR to re-issue advisories on November 9. By that time, the outflow improved, although it maintained multiple circulations. Atang passed near the north coast of Madagascar on November 10 after turning to the west, and that day the JTWC again discontinued advisories. After another period of re-organization, the agency again re-issued advisories on Atang on November 11 over the Mozambique Channel. The next day, the system moved inland in south-eastern Tanzania, and dissipated shortly thereafter.
In northern Mozambique, Atang produced moderate but beneficial rainfall in Cabo Delgado Province. (accessed via Lexis Nexis on 2013-04-28) The landfall area does not usually experience tropical cyclones, and damage in Mozambique was minimal. In Tanzania, there were unofficial reports that Atang killed several fishermen and caused heavy rainfall with wind gusts to .
Tropical Cyclone Boura
A strong area of winds near the equator developed an area of convection on November 14 to the east-north-east of Diego Garcia. It quickly developed outflow and a distinct circulation, becoming a tropical depression late on November 14. Early on November 15, MFR upgraded the system to Tropical Storm Boura, and later that day the JTWC initiated advisories on Tropical Cyclone 03S. With a ridge to the south-east, the storm moved quickly southwestward. Easterly wind shear prevented significant intensification until the circulation became established beneath the convection. On November 17, Boura intensified to reach 10-minute winds of , making it a tropical cyclone. The JTWC upgraded Boura to the same intensity that day but in 1-minute winds, or the equivalent of a minimal hurricane. The cyclone intensified slightly further to peak winds of .
Boura maintained its peak winds for about 18 hours, during which wind shear began to increase. The cyclone weakened as it curved more to the west, a change due to a ridge to the south. The JTWC estimated that Boura maintained peak winds of . Initially, the storm retained good outflow and convection, and Boura passed just north of St. Brandon on November 19, producing of rainfall and wind gusts of . While the storm turned to the west and northwest, it interacted with the ridge to the south to produce wind gusts of on Mauritius and Réunion, respectively. The convection gradually diminished, and on November 22 Boura weakened to tropical depression status while the JTWC discontinued advisories. The circulation continued to the northwest, devoid of convection. After turning to the north-east on November 25, Boura dissipated a day later north of Madagascar.
Tropical Cyclone Crystal
For several days in mid-December, tropical cyclone forecast models anticipated a storm to form to the south-west of Diego Garcia, which was proven true when an area of convection formed in that area, becoming a tropical disturbance on December 21, the fourth of the season. On December 23, MFR upgraded the disturbance to a tropical depression, and later that day to Tropical Storm Crystal. The storm moved southwestward toward Mauritius due to a ridge to the south-east. Strengthening was gradual, and the JTWC upgraded Crystal to the equivalent of a minimal hurricane late on December 24. The next day, an eye developed, although dry air initially prevented much further intensification. MFR upgraded Crystal to tropical cyclone status on December 26, and that day the cyclone passed just east of St. Brandon. Subsequently, Crystal intensified quickly after the eye became clearer, reaching peak winds of on December 27. Around that time, the storm passed east of Mauritius as it turned to the south while rounding the ridge. After maintaining peak winds for about 18 hours, Crystal weakened, gradually undergoing extratropical transition. The convection diminished over the center, and Crystal weakened to tropical storm status on December 28. The next day, the JTWC and MFR discontinued advisories, labeling the storm as extratropical. The remnants continued to the south-east, dissipating on January 3 after crossing into the Australian region.
While passing just east of St. Brandon, Crystal produced wind gusts of . The storm initially threatened to strike Mauritius, but effects were minimal due to the island being on the dry south-west quadrant of the storm. Crystal produced wind gusts of . Rainfall reached , although minimal precipitation occurred in northern Mauritius.
Severe Tropical Storm Delfina