The 1985–86 South-West Indian Ocean cyclone season was the first in which the Météo-France office (MFR) on Réunion tracked cyclones as far east as 90° E in Indian Ocean, south of the equator. Previously, the agency's area of responsibility was limited to 80° E. It was an active season with twelve named storms, of which five strengthened into tropical cyclone with 10 minute sustained winds of at least . The first named storm was Tropical Storm Alifredy, which originated in the Mozambique Channel in late December and moved across Madagascar. However, the unofficial Joint Typhoon Warning Center (JTWC) tracked a short-lived storm in September.
Most of the activity occurred in 1986, with four storms in January, three of which briefly existed simultaneously on January 10. The first of these three, Tropical Storm Berobia, struck eastern Mozambique. Tropical Storm Costa was a series of three tropical depressions within the same broader system that persisted for 12 days, bringing gusty winds and rainfall to the Mascarene Islands. The strongest storm of the season, Erinesta, formed in late January and struck the tiny Tromelin Island, decimating the native rabbit population. Erinesta later produced of rainfall in the mountainous peaks of Réunion, one of the highest 24‑hour rainfall totals at the time at Cilaos. Two other storms in February – Filomena and Gista – moved southward for their durations and did not significantly impact land. In March, Cyclone Honorinina killed 99 people and caused $150 million (1986 USD) in damage when it struck eastern Madagascar. There were two other storms in March, Iarima and Jefotra, the latter of which brushed Rodrigues island with gusty winds. The final two storms of the season, Krisostoma and Lila, entered from the Australian basin in April and May, respectively, with Lila exiting the basin to end the season on May 10.
Seasonal summary
During the season, the Météo-France office (MFR) on Réunion island issued warnings in tropical cyclones within the basin. Using satellite imagery from National Oceanic and Atmospheric Administration, 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. In September 1985, their area of responsibility shifted from 80° E to the current 90° E, although lack of satellite imagery along the eastern periphery prevented complete coverage. The World Meteorological Organization would later label the MFR as a Regional Specialized Meteorological Center in 1993. The Joint Typhoon Warning Center (JTWC), which is a joint United States Navy – United States Air Force task force, also issued tropical cyclone warnings for the southwestern Indian Ocean. The season's twelve named storms was well above the average of nine, while the five tropical cyclones – storms attaining maximum sustained winds of at least – was average.
The MFR considered the tropical cyclone year to begin on August 1 and continue to July 31 of the following year. By December 1985, water temperatures were cooler than normal across the Indian Ocean. However, the monsoon intensified the following month, allowing for increased tropical cyclogenesis. There were no El Niño conditions by March.
In addition to the storms tracked by the MFR, the JTWC followed a short-lived tropical storm in September. Classified as Tropical Cyclone 01S, the storm developed on September 23 to the east-southeast of Diego Garcia, which is an atoll in the central Indian Ocean. It failed to intensify beyond peak 1 minute winds of , and after passing south of Diego Garcia, the storm dissipated on September 29 south of the Seychelles.
Systems
Tropical Depression Alifredy
On December 23, a tropical depression formed in the Mozambique Channel, accompanied by spiral rainbands toward the center. That day, the system reached peak winds of , and the Madagascar Meteorological Service named it Alifredy. The storm moved quickly southeastward toward Madagascar. High pressures to the south prevented much development, and Alifredy moved ashore near Morondava in western Madagascar on December 24 at peak intensity. While crossing the island, the storm weakened into a tropical depression. Alifredy emerged into the open Indian Ocean and failed to restrengthen. It became extratropical and turned southeastward, dissipating on December 27 within the westerlies. The JTWC did not track the storm. Alifredy had little impacts on Madagascar; Morombe reported a peak wind gust of .