The 2007–08 South-West Indian Ocean cyclone season was the third most active tropical cyclone season, along with the 1985–86 season and behind the 1993–94 season and the 2018–19 season, with twelve named tropical cyclones developing in the region. It began on November 15, 2007, and ended on April 30, 2008, with the exception for Mauritius and the Seychelles, which ended May 15. These dates conventionally delimit the period of each year when most tropical cyclones form in the basin, which is west of 90°E and south of the Equator. Tropical cyclones in this basin are monitored by the Regional Specialised Meteorological Centre in Réunion.
Seasonal summary
Systems
Tropical Cyclone 01U
On July 26, a tropical disturbance developed within a near-equatorial trough. The next day, convection began to develop around the low while located about east of Diego Garcia. Moderate wind shear temporarily caused the convection to become displaced from the center on July 27. However, later that day, the Joint Typhoon Warning Center (JTWC) assessed the chances of the low developing into a tropical cyclone as "fair". By July 29 the low was designated as Tropical Disturbance 01 while located near the edge of Météo-Frances area of responsibility. With developing banding features, increasing convection and very warm sea-surface temperatures (exceeding ), the JTWC issued a Tropical Cyclone Formation Alert for the low as they assessed the chances of development of a tropical cyclone within 48 hours as "good".
In the post-storm report issued by the Australian Bureau of Meteorology, the system was estimated to have become a Category 1 cyclone, with winds peaking at , shortly before leaving Météo-Frances area of responsibility early on July 29. After leaving Météo-Frances area of responsibility, the JTWC designated the storm as Tropical Cyclone 01S. In Météo-Frances post-storm analysis, the disturbance was declassified as a tropical cyclone and the numbering, 01, was removed for unknown reasons.
Tropical Disturbance 01
The first officially recognized tropical disturbance developed early on October 10. The disturbance featured persistent convection around an elongated low level circulation located about west-northwest of Diego Garcia. With marginally favorable. conditions for further development, the JTWC assessed the chances of the low developing into a tropical cyclone as "poor". Further development took place later that day, with banding features developing and deepening convection as it traveled towards the south-southwest. In response to the increased development, the JTWC increased the chances of a tropical cyclone developing to "fair". On October 12 Météo-France designated the system as Tropical Disturbance 01–20072008. However, little or no further development was expected.
Late on October 12 through early on October 13, Dvorak Technique intensity estimates for the low from the JTWC reached T2.5—the equivalent of a minimal tropical storm—and there was a possibility that the system was briefly a tropical storm by one-minute standards. Despite favorable upper-level conditions and low wind shear, the disturbance was situated over cool sea-surface temperatures which provided little energy to fuel convective activity. With little thunderstorm and shower activity development, Météo-France issued their final advisory on the dissipating low the next day. Since the disturbance never impacted land, there were no reports of damage or injuries from it.
Severe Tropical Storm Lee–Ariel
On November 13, the Australian Bureau of Meteorology (BoM) began monitoring a tropical low situated about northwest of the Keeling Islands. The next day, the low was upgraded to a Category 1 cyclone and given the name Lee. Shortly after being named, the JTWC issued a Tropical Cyclone Formation Alert as deep convection persisted around the center of circulation. The system was moving towards the southwest within an area of moderate wind shear. Several hours later, the JTWC designated Lee as Tropical Cyclone 03S. With continued development, Lee strengthened into a Category 2 cyclone, according to the BoM, with winds of 10-minute winds). At 1200 UTC, Lee crossed into Météo-France's area of responsibility at peak intensity. Upon entering their AoR, it was given a second name, Ariel, and designated as a severe tropical storm.