Idylle originated in the Mauritius Region of responsibility and was a severe storm with gales to within 650 km of the centre at peak intensity, according to the Mauritius cyclone warning centre. It exhibited recurvature and began moving southeast on 10 April 1979 and steadily accelerated. The Guam TCWC estimated the system reached peak intensity on 12 April 1979 with maximum winds near the centre of 240 km/h and gusts to 295 km/h. The system then steadily weakened until 16 April 1979. between 16 and 18 April, however, the system became cold cored and intensified. A ship about 190 km from the centre reported force 10 winds. Gale warnings were re-issued for shipping and also for southwest Western Australia. Although gale force winds were reported along the southern west coast they were not sustained except near Cape Naturaliste and Cape Leeuwin. The only significant damage reported was some erosion at Perth metropolitan beaches.