The 1990–91 South-West Indian Ocean cyclone season was fairly quiet, although activity began early and the final named storm formed at a record late date.

Activity remained minimal until January, when Tropical Storm Alison formed in the eastern portion of the basin.

Cyclone Cynthia developed rapidly in the Mozambique Channel on February 16 and struck western Madagascar, killing 36 people and ruining local rice harvests.

Toward the end of the month, Tropical Storm Elma exited the basin into the adjacent Australian region, only to re-enter the south-west Indian Ocean and dissipate.

Long-lived Cyclone Fatima originated in the Australian basin in late March and changed directions before becoming extratropical.

The agency estimated intensity through the Dvorak technique, and warned on tropical cyclones in the region from the coast of Africa to 90° E, south of the equator.

Beginning in November 1990, MFR utilized a high resolution picture transmission station in conjunction with its satellite imagery.

[3] In general, the monsoon was weaker than normal within the basin, which provided less flow across the equator to spawn tropical cyclones.

[3] A southward-moving anticyclone influenced the monsoon trough to spawn a tropical disturbance on January 8, located east of Diego Garcia.

[6] Conditions favored further strengthening,[5] and Alison gradually intensified to peak 10‑minute sustained winds of 115 km/h (71 mph) on January 15, according to the MFR.

[7][8] While passing near Rodrigues, Bella produced strong winds and high tides, the latter of which caused flooding in the capital Port Mathurin.

On February 15, deep convection increased greatly,[8] leading to a tropical disturbance forming at 06:00 UTC the next morning.

[2] Moving southeastward, the convection quickly organized around the center, aided by warm sea surface temperatures and convergence.

Late on February 16, the system intensified into Tropical Storm Cynthia while it was passing near Juan de Nova Island.

Continuing to rapidly intensify, Cynthia attained tropical cyclone status on February 17, reaching peak winds of 125 km/h (78 mph).

After initially moving to the south, the system turned more to the southwest toward Mozambique on February 24, developing an eye feature in the center.

The MFR reported that the subtropical depression attained gales on February 25, by which time the JTWC already estimated winds of 140 km/h (87 mph).

By February 28, Debra had weakened to minimal tropical storm status while accelerating to the southeast, although it briefly re-intensified the next day.

In contrast, the MFR estimated Emla continued to slowly intensify to a 10‑minute peak strength of 105 km/h (65 mph) on March 1.

Shortly thereafter, the storm crossed 90° E into the Australian region, where the Bureau of Meteorology estimated that Elma entered at tropical cyclone status.

[20] On March 21, the MFR identified a tropical disturbance in the Australian region, which crossed into the south-west Indian Ocean on the next day.

[20] On March 25, the JTWC upgraded Fatima to the equivalent of a minimal hurricane, although the MFR only estimated 10‑minute winds of 95 km/h (59 mph) at that time.

[21] Due to a break in the ridge,[20] Fatima turned toward the south on March 26, around the time that the JTWC estimated peak 1‑minute winds of 165 km/h (103 mph).

Fatima turned back to the southeast on March 31 and accelerated,[21] weakening to tropical storm status due to upper-level wind shear.

[20][21] On March 30, an area of convection spawned a small tropical disturbance about 310 km (190 mi) east of Toamasina off the eastern coast of Madagascar.

[8] On June 7, the system passed south of the Chagos Archipelago,[23] and on the next day the JTWC classified it as Tropical Cyclone 22S, the final of the season.

[3][27] On the next day, the JTWC classified the system as Tropical Cyclone 04S, and assessed the storm as intensifying to a peak of 100 km/h (62 mph); the intensification was aided by an anticyclone aloft.