Complex sentence: At 0400 UTC on 5 December, TCWC Perth, having assumed local area responsibilities for the tracking of the storm, determined the system to have strengthened into a tropical cyclone; thus, the warning center assigned the name "Sam" to the storm.
Split into simpler sentences: At 0400 UTC on 5 December, TCWC Perth, having assumed local area responsibilities for the tracking of the storm, determined the system to have strengthened into a tropical cyclone. As such, the warning center assigned the name "Sam" to the storm.