Oscar was the first cyclone for the 1983-84 season and developed from a low pressure system located to the northwest of Cocos Island on 22 October 1983. The low formed to the south of a well-defined monsoon trough lying east-west along 4°S. Development continued and the system reached cyclone intensity around 0600 UTC 24 October.. Under the influence of upper-level easterlies, Oscar moved rapidly westward before recurving and assuming a southeast track as a result of the approach of an upper-level trough to the south.
Just after 0000 UTC 26 October Oscar began to move slowly westward again due to an easterly flow associated with a southern high. Following the slow collapse and eastward progression of this high, the cyclone moved slowly southwards and intensified and became a severe cyclone by 1800 UTC 27 October.
Oscar reached its lowest estimated central pressure of 968 hPa at 0900 UTC 28 October. From 2100 UTC Oscar began to weaken steadily due to its passage over cooler waters and also because of strengthening northwest winds over the system ahead of an upper-level trough. No eye was visible from the Japanese Geostationary Meteorological Satellite (GMS-2) imagery. Cyclone intensity was lost around 0000 UTC 30 October.
The remnants of Oscar then tracked to the southwest during the next two days and became embedded in a low pressure system of southern .origin. The highest wind speed associated with Oscar was 83 km/h recorded by a ship 230 km to the south-southeast of the centre at 0600 UTC 26 October.