The eighth named storm of the season, Hyacinthe formed on January 15, 1980, to the northeast of Mauritius in the southern Indian Ocean.

Initially it moved to the west-southwest, and while slowly intensifying it passed north of the French overseas department of Réunion.

For twelve days, Hyacinthe dropped torrential rainfall on Réunion; nearly all of the island received more than 1 m (3.3 ft) of precipitation.

The heaviest rainfall occurred through a process called orographic lift in the mountainous interior, leading to hundreds of landslides.

In the middle of January 1980, the Intertropical Convergence Zone persisted along 10° S, spawning a small low-level circulation near St.

[3] That day, the Joint Typhoon Warning Center (JTWC) also reported that a tropical depression had developed, giving it the identifier "08S".

[4] That day, an eye developed,[1] and MFR estimated that Hyacinthe intensified to tropical cyclone status, with 10-minute winds of 120 km/h (75 mph).

After approaching within 175 km (109 mi) west-southwest of Réunion, the cyclone turned to the northwest and executed another loop.

The JTWC estimated that Hyacinthe reached peak winds of 130 km/h (81 mph) on January 25, which the storm maintained for about 24 hours.

[8] Such heavy rainfall typically occurs on the island when tropical cyclones approach, owing to orographic enhancement in the mountainous interior.

[8] In addition to the rainfall, Hyacinthe produced a minimum barometric pressure of 977.8 mbar (28.87 inHg) at Saint-Pierre on January 27.

[5] Three towns were temporarily isolated,[5] including Hell-Bourg which was cut off for about eight days,[12] Helicopters delivered food and clothing to the villages.

[5] Many records set by the storm were broken by Cyclone Gamede in 2007, including the rainfall accumulations from three to eight days.