Though a subtropical ridge was forcing the cyclone westward at the time, an approaching shortwave trough caused Sam to track southward the following day, towards the Australian coast.

Offshore, 163 illegal immigrants aboard two vessels were feared to have drowned, which would make Sam one of the deadliest cyclones in Australian history.

During an active Madden–Julian oscillatory period over Australian longitudes in late November,[1][2] a broad low-pressure area developed within the monsoon trough in the southeastern Arafura Sea, west of Cape York Peninsula.

[5] Due to weak steering currents, the depression drifted southward and moved ashore the Kimberley coast roughly 90 km (55 mi) east of Kalumbaru; this stint over land was short lived, however, and the system tracked back westward, reentering the warm Timor Sea the following day.

[3] At 0400 UTC on 5 December, TCWC Perth, having assumed local area responsibilities for the tracking of the storm,[2] determined the system to have strengthened into a tropical cyclone.

[3] During the evening hours of 6 December,[3] however, Sam began to interact with a shortwave trough, causing the cyclone to curve southward and towards the northwestern coast of Australia.

[3] Continuing to intensify, TCWC Perth upgraded the cyclone to Category 5 intensity at 2000 UTC, with winds of 195 km/h (121 mph) and a minimum pressure of 950 hPa (mbar; 28.06 inHg).

[1][2][3] However, in post-storm analysis, it was analyzed that Sam had had in fact peaked with winds of 205 km/h (127 mph) and a minimum pressure of 935 hPa (mbar; 27.61 inHg).

[4] After a brief period of restrengthening over central Australia on 13 December, Sam finally weakened below tropical cyclone intensity the following day before dissipating shortly thereafter.

[10] Due to the storm's impending threat to the northwestern coast of Australia, most of the residents of Bidyadanga and Anna Springs Station were evacuated via helicopter.

[3] Roughly 600 mi (970 km) off the coast of western Australia, two illegal immigration vessels departing from Indonesia and bound for the Ashmore Islands was caught within Cyclone Sam.

A weather station in Shelamar near the point of landfall recorded 520 mm (20 in) of precipitation in a 48-hour period ending during the morning hours of 11 December.