2004–05 South-West Indian Ocean cyclone season

The 2004–05 South-West Indian Ocean cyclone season was a near average season, despite beginning unusually early on August 30 with the formation of an early-season tropical depression. Météo-France's meteorological office in Réunion (MFR) ultimately monitored 18 tropical disturbances during the season, of which 15 became tropical depressions. Two storms – Arola and Bento – formed in November, and the latter became the most intense November cyclone on record. Bento attained its peak intensity at a low latitude, and weakened before threatening land. Tropical Cyclone Chambo was the only named storm in December. In January, Severe Tropical Storm Daren and Cyclone Ernest existed simultaneously. The latter storm struck southern Madagascar, and five days later, Moderate Tropical Storm Felapi affected the same area; the two storms killed 78 people and left over 32,000 people homeless. At the end of January, Severe Tropical Storm Gerard existed as an unnamed tropical storm for 18 hours due to discrepancies between warning centers.

After a series of weak tropical systems in February, there were two storms in March. Severe Tropical Storm Hennie brought heavy rainfall to the Mascarene Islands, and Severe Tropical Storm Isang remained away from land. The season's strongest storm originated in the neighboring Australian basin, developing in early April near the Cocos Islands. After being named Adeline by the Australian Bureau of Meteorology (BoM), the MFR renamed the storm Juliet once the storm crossed 90°E. Juliet would reach maximum sustained winds of , making it a very intense tropical cyclone. Juliet damaged corn plantations on the island of Rodrigues before becoming an extratropical cyclone on April 11, thus ending the season.

__TOC__

Seasonal 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. The agency tracked 18 tropical disturbances, including one zone of disturbed weather that lasted for one advisory, which was higher than normal. The agency assessed that 15 disturbances reached tropical depression intensity. Ten of these weather systems intensified into named storms, which was one higher than normal. There were 44 days in which a named storm was active, lower than the average of 53. There was an unusual period of inactivity across much of the basin from January to March, typically the most active months. During this time, the Intertropical Convergence Zone was located farther south than usual, causing any developing storms to reach their peak intensity at higher latitudes. The exception was southern Madagascar, which was affected by Cyclone Ernest and Tropical Storm Felapi in a five-day span in late January. Four of the named storms attained maximum sustained winds of at least , the threshold for tropical cyclone intensity; this was also near normal. Three tropical cyclones strengthened into intense tropical cyclones, including Very Intense Tropical Cyclone Juliet.

In addition to the MFR, the American-based Joint Typhoon Warning Center issued warnings for cyclones in the basin, as well as the entire southern hemisphere. The agency did not track Tropical Storm Felapi, and it estimated that a tropical depression in October attained tropical storm status.

Systems

Tropical Depression 01 (Phoebe)

On August 30, an area of low pressure developed near the edge of Météo-France's area of responsibility within an unseasonably active monsoonal band which coincided with the Madden–Julian oscillation. Tracking towards the southeast, the low experienced strong deep-level wind shear which kept most of the convection displaced from the center of circulation. On August 31, convection managed to develop around the west and southwestern portions of the low, and was designated as Tropical Depression 01. The depression reached its peak intensity at this time with winds of 55 km/h (35 mph 10-minute winds) and a minimum pressure of 999 hPa (mbar). Shortly after, the depression entered Australian Bureau of Meteorology in Perth's area of responsibility. The depression later intensified into a tropical cyclone and was named Phoebe.

Tropical Depression 02

Toward the end of October, low-pressure areas developed on both sides of the equator in the west-central Indian Ocean. The system in the North Indian Ocean failed to develop, but the Southern Hemisphere system became Tropical Disturbance 02 on October 25. Moving westward, the disturbance had an organized area of thunderstorms near the center, with favorable conditions provided by the subtropical ridge. The MFR upgraded the disturbance to a depression on October 26, and briefly downgraded the system after the circulation became exposed, only to upgrade it again to a depression the next day. The JTWC initiated warnings on the system as Tropical Cyclone 02S on October 27, estimating 1-minute winds of . That day, the system passed about north of Madagascar. Wind shear in the region caused the storm to weaken again. On October 29, the weak disturbance moved ashore in eastern Tanzania near Dar es Salaam, dropping heavy rainfall.

Severe Tropical Storm Arola

The near-equatorial trough spawned an area of convection east of Diego Garcia on November 6, which the MFR classified as a tropical disturbance. The system slowly organized amid favorable conditions, including low to moderate wind shear. On November 8, the MFR upgraded the system to a tropical depression and later Moderate Tropical Storm Arola, and the JTWC classified it as Tropical Cyclone 03S. Steered by a ridge to the south, Arola moved southwestward at first while quickly intensifying. Late on November 8, the MFR estimated peak winds of , making Arola a severe tropical storm. Early the next day, the JTWC upgraded the storm to the equivalent of a minimal hurricane, estimating peak winds of . The storm turned to a westward drift, entering an area of higher wind shear and cooler waters, which caused Arola to weaken. On November 12, the MFR downgraded the storm to a tropical depression, by which time the storm was moving southwestward again, passing south of Diego Garcia. The JTWC discontinued advisories the next day. The MFR tracked Arola until November 18.

Intense Tropical Cyclone Bento

On the same day that Arola dissipated, the near-equatorial trough spawned another area of convection east of Diego Garcia. A day later, the MFR classified the system as a tropical disturbance as the thunderstorms organized and consolidated, amid favorable conditions. On November 20, the MFR upgraded the system to Tropical Storm Bento, and the JTWC initiated advisories as Tropical Cyclone 04S. At first, Bento drifted to the southeast, but turned to the west two days later. The MFR upgraded the storm to tropical cyclone status on November 22, the same day that the storm began a rapid intensification phase. On November 23, the MFR estimated peak 10 minute winds of , and the JTWC estimated peak 1 minute winds of , equivalent to a Category 5 on the Saffir–Simpson scale. This made Bento among the most intense tropical cyclones in the basin within 10º of the equator, only surpassed by Cyclone Fantala in April 2016. It also made Bento the strongest cyclone in the basin in the month of November, surpassing Cyclone Agnielle in 1995.

Around its time of peak intensity, Bento was located far away from land – about 325 km (200 mi) east-southeast of Diego Garcia. It was also moving southwestward due to a ridge to its southeast. On November 24, the cyclone began weakening due to an eyewall replacement cycle, as well as the presence of drier air and increased wind shear. A day later, Bento turned to the southeast, steered by a passing trough. The MFR downgraded the cyclone to tropical storm status on November 26, but upgraded it back to tropical cyclone status a day later. By late on November 27, the circulation was exposed from the convection. Bento turned to the west and failed to reintensify due to cooler waters. The JTWC discontinued advisories on November 29, but the MFR continued tracking the system as a tropical disturbance until December 3, when Bento was passing north of the Mascarene Islands.

Subtropical Depression 05

On December 11, the MFR issued two bulletins for Subtropical Depression 05. The system formed about halfway between the southern tip of Madagascar and the west coast of Mozambique, and failed to intensify.

Tropical Cyclone Chambo

In the middle of December, the near-equatorial trough spawned an area of convection to the west of Indonesia. For several days, the system drifted westward through an area of minimal wind shear. On December 22, the MFR classified the system as Tropical Disturbance 6 to the northwest of the Cocos Islands. By that time, the thunderstorms were increasing and consolidating. The JTWC classified the system as Tropical Cyclone 06S on December 23. On the next day, the MFR upgraded the system to Moderate Tropical Storm Chambo. The storm quickly intensified as it moved southwestward, steered by a ridge to its southeast. On December 25, the MFR upgraded Chambo to tropical cyclone status, and the next day estimated peak 10 minute winds of . The JTWC meanwhile estimated peak 1 minute winds of . Cooler waters and stronger wind shear caused Chambo to begin weakening on December 27. By the next day, the circulation became exposed from the thunderstorms, and the JTWC discontinued advisories. On December 30, the MFR reclassified Chambo as an extratropical cyclone. The storm turned to the south and later southeast, and was last mentioned by the MFR on January 2.

Tropical Depression 07

On January 4, the MFR began issuing warnings on Tropical Depression 7 in the Mozambique Channel. The system moved southeastward, moving ashore western Madagascar between Morombe and Toliara on January 5, and quickly dissipated.

Intense Tropical Cyclone Ernest

An area of convection developed west of Diego Garcia on January 16, prompting the MFR to classify it as Tropical Disturbance 8. A day later, the agency briefly discontinued advisories, only to resume them on January 19 as the disturbance passed north of Madagascar. That day, the JTWC classified the system as Tropical Cyclone 12S. On January 20, the MFR upgraded the system to Tropical Storm Ernest to the east of the Comoros. The storm quickly intensified, and within 12 hours of being named, the MFR upgraded Ernest to tropical cyclone status. The cyclone turned to the south through the Mozambique Channel, attaining peak winds of on January 22, according to the MFR. The JTWC estimated peak 1 minute winds of . On the next day, Ernest turned southeast and made landfall in extreme southern Madagascar, near Itampolo. It quickly emerged over open waters and weakened. On January 24, the MFR reclassified Ernest as an extratropical cyclone, tracking it for one more day.

In southern Madagascar, Ernest produced high wind gusts, reaching in Toliara. The same town recorded heavy rainfall during the storm's passage, totaling over 24 hours. Ernest's Madagascar impacts were followed by Tropical Storm Felapi five days later. Ernest killed 78 people in Madagascar. Collectively, Ernest and Felapi damaged 5,792 buildings, which left 32,191 people homeless. Madagascar's National Emergency Centre deployed workers to do search and rescue missions and provide water to storm victims. The World Food Programme provided 45 tons of rice to affected residents, although persistent flooding disrupted relief work.

Severe Tropical Storm Daren